code 51/ quits when returning to idle

[professorbob]

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?

[cre]

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. 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.

[professorbob]

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

[cre]

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?

[cre]

Here you go:

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




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

[professorbob]

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

[cre]

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.