code 51/ quits when returning to idle
 

1989 Turbo Targa with automatic transmission. After transmission rebuild and reinstall of engine and transmission, (See other post) the car ran great for 125 miles. Then suddendly at about 70mph started balking and dropped into limp home mode. Initial symptoms indicated possible bad fuel pump. Fuel pump replaced. and No joy....
The intake horn was cleaned during engine refresh of blow-by oil. Because the Turbo uses a Vortex generator, this UNIT SHOULD NEVER BE CLEANED as damage will occur. (Dealer price 700.00) Purchase a used replacement electronics on Ebay. Still not joy. This unit had the black sealer so it was not from a 1989 year car.
Found a local Supra owner who removed his good electronic meter and installed it. The performance improved by still not out of limp home mode. The new valve cover gaskets were leaking because the screw had worked loose. Tightening the gasket screws seems to help the problem. Have removed the Idle Air Control and Throttle Position Sensor for trouble shooting. Will now have to replace the large hose as it broke upon removal. Anyone have a source for pre formed hoses other than the dealer?
Are the IAC and TPS available as aftermarket parts?
All ideas and suggestions are welcome.

Every condition which would cause "Limp Mode" should record a code in the ECU or the ECT. Code 52 is the only one that's commonly seen on these cars. The TPS and ISCV will NOT cause the car to go into limp mode, just idle issues and poor throttle transition response. Code 51 only mean that the A/C is on or there's a problem in that circuit OR The throttle is open or there's a problem with the idle switch (IDL) in the TPS.... if you're on the throttle or have the A/C on the code will show up but will clear a few seconds after you get off the throttle or turn off the A/C. Note that you cannot set ignition timing with code 51 (or any other code) present and you MUST make sure to install the diagnostic jumper when doing so. Is the ECT light on or flashing? Any code 52?

Idle Control Valve ??
 

Car still operating rich and will not shift out of second gear and engine is being held to less than 2,000 under driving load.
Checked the Throttle Position Sensor TPS and it checks OK. Idle Control Valve ICV is carbonized and used some cleaner on the plunger. Is the plunger suppose to close completely? I can suck air through the port even when closed.
Any sources for replacement parts other than dealer.
The A/C is no longer cooling. It performed well for the time the vehicle was working. I had added a can of freeze 12 then. Non only warm air. Maybe this is the reason for the code 51.

I am looking for a safe way to check the vacuum hose joints. Suggestions. Someone suggested pressurizing the vacuum system at the hose from the carbon canister and applying bubble soap.
Still looking for source for form hoses. Any suggestions are appreciated.
So want to get back in the road again.
Is there a standard reason for tripping into limp home mode?
Thanks
Prof.

Rpm cut back..Blown exhaust header gasket and rich condition???.
 

Still trying to get the supra back on line... Finally have an inside area with heat to do the work. Update. Car ran great for 120 miles then started cutting out and now will not operate above 2000. I have lost the gasket between the manifold and header I installed new when the engine went back in.
After some effort of multiple tries and seeming more fuel being added with each try the engine will start and seem to go through the normal warm up as required. I suspect that the difficult start is fouled plugs. As the normal operating temp is reached and rpm come back the engine goes through occasional hesitation. I can apply throttle until about 2300 rpm when it acts as though the ignition has been momentarily stopped until it goes back to idle speed. There is a very rich condition and soot is blowing out around the header. I have a replacement gasket ordered.
Can a clogged converter cause enough back pressure to cause a gasket blowout and these issues. The rear exhaust seem to be normal.
If so is there a way to determine converter condition without removing the exhaust again.
What about a bad O2 sensor as the one on the turbo housing. IF it is bad will that create these issues?
All suggestions are appreciated.

I am going to check codes, but expect that I have not been able to operate the engine long enough for the on board diagnostics OBD to make a check.

A clogged cat is a possibility, especially after a rebuild. I'd test the AFM first. You haven't sprayed the AFM out with any water or cleaners I hope. Also, if you have any error codes present you cannot set the ignition timing... This may account for part of the problematic behavior.

No, a bad O2 sensor will not affect your fuel mixture to this degree. The ECU does not even use the O2 sensor until the vehicle is up to normal operating temps.

Clear any existing codes and see if any new ones are set. Some codes may show immediately if there is a problem with a component such as 24, 31, 41, 51, 52 (these are the more common error codes); A lean condition or rich condition or O2 sensor fault code will not show up until the vehicle is up to operating temp and has been driven. Depending on what the defect is some codes may show up right away or not until later such as AFM related codes like 24 and 31; So if you don't see these right away don't dismiss the AFM as a suspect.

Blown Exhaust header gasket continued.
 

Thanks Cre for the rapid response. As you can gather, these issues have been ongoing for over 6 months.... See previous post for updates... I actually replaced the AFM module with a used unit, because I too had no clue that cleaning the module would kill it.
Thought originally that that is why the car started these issues after 120 miles, because the new replacement was used, borrowed a functional unit to determine if that is the issue. Very little improvement. Do you know of anyone I may send my unit too for a proper diagnositic of the modules.

This most recent problem with the blow gasket is what makes me believe there is a restriction in the converter. Just do not know how much restriction is required to cause the gasket to blow.
Is there an effective way to determine it the turbo is operating properly. I understand that it lays out unless the vehicle is driven.
My turbo needle is below 0 on the boost gauge.


The gasket arrive just now and I will be jacking the vehicle to remove the header for reinstallation.

It's going to be loud as hell, but pull off the cat and take it for a quick spin around the block.

Converter Removal
 

When I separate the header, a road test may not be necessary. If there is a backup, the relieved pressure may very well allow me to do Wide Open Throttle WOT test without the cut back to idle. If it does then I will have solved a months long mystery. Keeping my fingers crossed. I will post what I find out.
Thanks
For the help.
Prof.

Over Rich and Dropping of at 2200 rpm.
 

Dropped the header just enough to ease out the gasket. Did not seem to be crushed.. Starter the car and let it warm a few minutes.
The engine did not start instantly. It required about four tries. Each time I move the switch back to off and waited a second. Each time the attempt to start was better until it kicked off.
It immediately went into warmup mode and after a few minutes dropped back to the normal idle position.
Each time I would accelerate through about 2200 rpm the engine would stop and allow rpm to drop about half before increasing again. Holding the accelerator at the same position would cause the increase and stop again and again.
Very rich condition exist with huge amounts of black smoke coming out the header. I do not believe that there is anything wrong with the exhaust system.
I do wonder about the gasket thickness in that it does not seem to be able to keep the tube from the down pipe sealed when it is bolted up against the header. Just wonder is there is one slightly thicker to stop the leakage. However, the one just removed was installed new at the last install.
Would the be considered a fail safe mode? If so what conditions exist to cause the computer to create this condition.
Would the transmission inputs cause this?
What about the fuel pressure regulation?
Am quite frustrated with not being able to determine what is causing this issue.
Finally I have a slight amount antifreeze dripping down the back side of the block. Just wonder how to make sure the hoses are tight enough.

Any help is appreciated.
Prof.

Put the car in diagnostic mode and run it. Watch for any codes (other than 51 which you'll set from pressing the throttle). It does sound quite a bit like limp mode. I can't think of anything pertaining to the transmission that would cause the car to respond like this, especially while stopped. It requires a significant problem for the ECU to enter limp mode... knock sensor fault, significant knock detected, sudden loss of oil pressure signal, faulty ECT, damaged wire harness and so on.

Fuel pressure is a possibility but I don't believe it is very likely... It won't hurt to check the pressure though.

Have you checked the mechanical timing and timing belt already?

I'll look back over this this weekend and see if/what I've missed and let you know if I can think of anything to check next. Worst case scenarios we start back at the top and work through the list.

No, Toyota does not make various thicknesses of exhaust gaskets. The gasket will compress somewhat after initial installation but nothing significant. The exhaust may just be hanging up on the studs in which case releasing the hangers may help.

How to make sure the hoses are tight enough.... hmm... No easy answer I'm afraid. If they're the right size you would just need to be sure the nipple is clean of buildup, corrosion and pitting and then use the proper constant tension clamp that Toyota put on at the factory. If you think the CT clamp has lost some of its elasticity then get another from Toyota. If you've switched to a worm gear hose clamp... well, just tighten until it stops. If it feels like it's too tight and is going to come apart, well, it probably is and there is something wrong with the nipple or the hose.

I know how you feel situations like this suck. You just need to make an actual list of how and what to check and in what order, set aside a few hours on Sat and Sun and hammer through it (TSRM in hand).

Fuel pump relay resistor is not to spec.
 

The relay check OK as per the manual... Decide to check values on the fuel pump resistor.... should be 0.70 ohms. Resistance is 1.4 on the 200 scale. Thinking this may be my problem, as it will not allow the pump to spool up as rpm increases.
Is there a method for direct wiring the pump relay to bypass the resistor in order to determine if this is causing the engine problems I am experiencing?
When sourcing a replacement resistor. Is the turbo GTE unit different that of the GE engine type.

Thanks
Prof.

The resistor is employed at LOWER RPM and load... not where you're experiencing the problems and it's not bypassed by the relay until around 4K at a medium or higher load, IIRC.... Besides, with higher resistance on it you'd be running lean, not rich. Do keep in mind that resistance varies depending on temperature too... but yes, that is a good deal higher than it should be.

You can bypass both relay and resistor by unplugging the large, round, yellow connector and jumpering the Blue wire with black stripe and the black wire with red stripe. Use heavy gauge wire.

The GTE and GE resistor packs should interchange just fine.

TPS Throttle Position Sensor check..
 

I ohm ed out the TPS. The throttle stop screw is not touching the rocker and there is about 1/16 inch of distance between the two in the completely closed position. The stop screw is seated against what I believe is the dash-pot diaphragm though.
The value is within speck in the completely closed but I was unable to set the feeler gauge for the two lower settings.
However the WOT Wide Open Throttle position has two reading and one is way out of scale.
I am wondering if this may be a contributing factor.
I expect at this point it would be OK to reinstall the header gasket to be able to operate the engine to establish another code set. I cleared the codes by pulling the DOME 20 fuse.

The engine should run fine with the TPS disconnected... it may have some trouble transitioning into idle and with tip in/out response. A bad TPS should have VERY little effect on the operation of the engine; It is only a trim sensor.

Dash lite question. ???
 

I have an indicator that is on that I have not noticed before. It is extreme left on the dash beside the temp gauge. Looks like a radiator with the cap above or something similar. Can you tell me what it indicates.
Thanks
Prof

Throttle Postion Sensor defective..
 

I reinstalled the exhaust header gasket and ran the engine to create codes. Started engine and allowed it to reach normal operating Temperature. RPM was still up when I pushed the accelerator pedal and it dropped back to about 800 which is in range. Slightly rough idle probably because of the excess soot. Tried to increase RPM and it would work up to 2800 quit until it dropped back to 16 1800 then come back up to the throttle position of 2800.
Shut it down and checked codes. 41 Throttle Position Sensor TPS... From your previous post about being able to run the engine without the TPS, I unplugged and restarted the engine. With the TPS disconnected I now am able to get the engine to reve to 3500, although still a little rough, which indicates the TPS may be the main problem here. I did not want to go any higher on the RPM without a load on the engine.
Question. Will an aftermarket TPS work, or should this unit come form Toyota. Thanks for your input in the search for my problems.

Also still wondering about the light on the dash as per above.
Thanks
Prof.

The lamp you describe is the 'low coolant' light. The sensor is in the reservoir... not really the best indicator if the whole system is low, but it's better than nothing.

Code 41 mean there is an actual short or a break in the circuit. While the TPS being 'out of whack' shouldn't cause significant drive-ability or operation issues a short most likely will. A removed TPS will create rough transitioning when abruptly revving the engine, transitioning to idle and may affect WOT performance at lower loads; Smooth transitions in throttle shouldn't really see rough operation. This code will set and remain stored if the TPS is unplugged... Are you still getting this code after a reset? (Without looking at my notes I believe) TPS signal (VTA) should read >480mV at full stop (closed throttle) and ~3.48V at WOT.

You could install a universal unit but you'll probably need to add a separate IDL switch and you'll also need to verify that it provides the voltage as detailed above and not a 0V to 5V signal... On top of adapting it to physically connect you'll want to consider that when deciding if it's worth it. I rather like converting over to more readily-available and common components on rarer vehicles... like GM knock sensors. :bigthumb:

Is the harness unmodified or has it been modified or shortened/lengthened at all?

Check your grounds, specifically E1 and E2. Also check Vc (should be ~4.8V at the TPS and AFM harness connectors with the ignition on or the engine running).

TSP issues...
 

Thanks for the rapid reply... I have the front of the vehicle on jack stands, and this may cause the coolant to be off the sensor. I'll check it and add coolant as required.
Regarding the aftermarket TSP... I would rather keep the vehicle as near authentic as possible and was not intending to us a universal unit, but a OEM type replacement just not from the dealer because of the extra expense. This vehicle is all original and has not been modified.
I will check NAPA or O'Rileys to see what they have specifically for this year model. Some suppliers carry the denso units.
Reference the ground check.
Check your grounds, specifically E1 and E2. Also check Vc (should be ~4.8V at the TPS and AFM harness connectors with the ignition on or the engine running).
Are you referring to the TSP harness plug, or at the Code reading terminal?
Unplugging the TSP stopped the cutting off at 2500 RPM and I could increase from Idle to 3500 with no hesitation. Just got to think there is a problem with the tsp circuit.
How would one go about checking the supply harness to the TSP. It has not been changed in any way.

Now that I am able to get the engine to act somewhat normally, and because I replaced the original MAF Karmon vortex sensor with a used unit not from the 89 model year, I am going to reinstall the original unit to see if that improves/or not the over rich condition.
I have read that the wrong MAF sensor can cause an over rich condition.
Your thoughts?

Points of clarification: It's TPS, Throttle Position Sensor; The 7M-GTE is paired with a KVAFM or AFM for short, Karman Vortex Air Flow Meter. The 7M-GE uses a VAFM or Vane Air Flow Meter (again AFM for short). A MAF (Mass Air Flow sensor) is a different type of device altogether... similar function just operates quite differently. (So many different devices.... such high prices for some and insane complexity with others really make me sooooo happy that there are even piggybacks out there which allow us to convert from one type of air meter to something cheaper or larger or more reliable such as a 3.5" GM MAF, GM MAP / IAT setup and so on).

The AFM did not change for any year; So unless the AFM you've installed is from a different vehicle the only thing which would cause any change is if it is in fact defective. I can't say it would be the first time I've heard of someone going through two (or five) only to find they were all bad. Now if you're referring to the Lexus 1UZ KVAFM then yes... BUT the electronic part of the assembly is still compatible, only the housings are different. The stock housing is a bit smaller than the Lex AFM. If you have a Lex and the original on hand you can install your KVAFM test it out and then swap in just the electronics from the Lex AFM and give it a go.

What I mean when I say to check E1 and E2 is for you to check all the grounds at the head of the engine. There should be one group on a separate stud on the lower part of the intake plenum and I believe another on the exhaust side by the firewall which connects to a stud by the mounts for the throttle linkage assembly... although there may only be one ground going from there to the firewall. Clean all surfaces with some sandpaper. Check the engine grounds too while you're at it; The grounds to the block and the driver's side fender.

Vc is the voltage supply for certain sensors. You should measure it at the AFM's connector and at the TPS' connector. Really if something were wrong with this line you'd most likely be seeing errors for at least the TPS and AFM (and possibly some others depending on the nature of the problem) but it's worth checking to be sure.

The TPS is a wear component which ideally should be replaced every 75K to 100K miles. As it's just a basic trim sensor a lot of them end up never being replaced and as long as the IDL switch doesn't go bad they may never get replaced during the life of the car.... That should give you a general idea of just how important they are to the vehicle's basic operation. :p No there are circumstances where they may cause some significant headache such as a short across other circuits but more often even those are harness problems and not a problem in the TPS itself.

RPM cutoff... Rich condition update after road test.
 

Added water and the low fluid light went out. Still have not located the drip at the back of the engine, and I expect that is where the coolant leaked out.
Leaving the TPS Throttle Position Sensor disconnected, I started the engine and allowed it to reach operating temperature.
Decided to drive it down the street a few block to see if there is any difference in performance.
Still no joy. The car will with hesitation to accelerate ( probably because of the disconnected TPS) it shifted from 1st to second but faltered before being able to up shift to High.
Tried to go to WOT Wide Open Throttle and had very poor response and still not increase in speed. The engine would cutoff at 2800 rpm. and drop back to 1800 where it again would try to gains speed.
Still have the very high rich mixture, as there is huge amounts of black smoke, as one would have on a carburetor engine with full choke.
After about 1/4 mile, I returned to the garage to check codes.
Had a 32,41,51.
For sure the 41 is the disconnected TPS. 32 is the turbo, or AFM or ECU.
I certainly wish there were a way to check values on these Karmon Vortex AFMs to make sure they are OK. Trying to contact another supra owner to ask if he will install these electronic units on his supra to see the response.
Will continue to read the manual this evening about checking values with ohm meter.
I noted that in some cases a analogue volt/ohm meter is recommended. Is there any special reason that a digital meter will not work.
I removed the ground screw for the real passenger side strap and scraped the brass fitting and hold down washer. Also did the same thing for the grown strap coming off the battery on the drive side wheel well.
I re-tightened the intake hoses to make sure there are no leaks.
The turbo gauge needle is just below the 0 indicator and drops to -4 at Idle. Is this normal. What should I look for from this gauge during the test drives. Under what conditions will the turbo response and in what manner base on shifting etc
51 indicates an issue with the A/C. I have the off button pushed, but still have lights on the circulation buttons. Is this normal or not?.

I know this is a lot of stuff to read and absorb and I appreciate you willingness to off input.
Thanks
Again.
Robert

32 is a short in the HAC circuit, not related to the turbo. I don't recall you Mentioning this previously. It's not shown in the 89+ TEWD because in the later model ECUs (mid89 and later) the HAC sensor was incorporated into the ECU itself. In early '89 and prior it was an external sensor mounted behind the glove box near the hinge... three wires. I think it too gets it's power from Vc as well as does the AFM... if so there's a very likely tie in. I believe both also use E2 as ground. Have you tested Vc? A short in the wiring harness or a bad ECU would account for all three related problems.

With regard to the TPS, I forgot to mention that automatic transmissions do rely on it more than manuals... in this case driving with it unplugged or damaged will probably result in even worse performance.... Which do you have?

Analog meters refresh more slowly so signals with oscillations are essentially averaged out. Reading Vf with a digital meter, for example, may show a bouncing signal which never stabilizes (say from 2.5 to 5V, back and forth and numbers in between).... with an analog meter it'll show 3.75 with only a slight flutter to the needle. Some DMMs do have a function to mimic this behavior.

The stock boost gauge is not a diagnostic tool by any means and I recommend you not expect anything more from it then you would from a 'dummy light'. The engine operates just like an N/A engine until the compressor starts spooling up; In vacuum. Until the compressor is spooling and producing enough compression to raise the manifold absolute pressure to ambient the engine remains in vacuum and any good boost gauge will reflect this.

You can test the KVAFM.... with Toyota's publication on advanced diagnostics and repair (this also covers ECU's, IIRC), a flow bench and an oscilloscope. I suppose you could test one with a leaf blower, an oscilloscope, a known good KVAFM (as reference) and the suspect KVAFM connected in series.... ;)

Yes, it's normal for the vent mode to remain lit as ling as the button is pressed. As long as the A/C switch is off (and it's LED, naturally) you're fine and barring a wiring issue the code 51 would only be caused by the TPS or a bad ECU.

Limp mode is only entered when a condition exists that the ECU believes is critical to an extreme degree. It doesn't even go into limp mode for a 'lean condition detected' error code, if memory serves correctly. Issues such as severe knock, damage to the ECU or malfunction of critical electronic components (there aren't many of there actually); I believe on the 7M-GTE an oil pressure signal of 0 at the ECU or at least a fluctuating oil pressure signal may cause it as well.... does your factory oil pressure gauge work?

Here you go:

http://www.supra.co.nz/87tsrm/EFI/efi121.htm




EDIT:
1987 TRSM: http://www.supra.co.nz/87tsrm/index.htm

Engine Stopping update
 

Thanks for the Link, I will check out the HAC High Altitude Control values.
After extensive reading at this site www.autoship101.com I learned there is a relation with the brake light switch and the engine control.
I have a panel light that indicates there is a problem with the brake lights.
Just wondering if you know which fuse controls the brake light circuit so I can remove it.
Am thinking that the ECU may be affecting the fuel cutoff because it thinks that the brakes are being applied.

I plan on purchasing a replacement Throttle position sensor as well because of the fact that it is out of spec. I am hoping this will also improve the starting on first try rather than the present 4- tries.
Thanks for you help.
Robert

The brake fuel trim is VERY minimal and is reliant on other sensor data from what I recall.... Otherwise, brake-boosting would be impossible in these cars but it's actually VERY easy.

Do keep in mind that those publications cover MANY years and many years of changes and evolution. A lot of it has no relevance with regard to TCCS and earlier systems.

Hi guys new to this forum, any update on this my son and I have been restoring a 1989. We had the head straightened and machined and a valve job done on it, reassembled the motor and are having the same issues that professerbob was having. Won't rev over 2500. changed the MAF and the TPS no vac leaks and no codes. I am going to check the grounds, but any other thoughts would be appreciated. My son is an eleventh grader in automotive tech and this has the teacher confused. Thanks