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Old 01-24-2011, 03:31 AM   #1
Fr0sTbY7eX
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Default Rough idle and low RPMs at startup when cold...

Hey guys, I'm a supra noobie but I've always loved the MKIII, just bought a 1990 supra turbo with a rebuild. HKS MHG, ARP head bolts etc. It's very, very clean. I'm having a problem with rough idle and low RPMs at start up. The check engine light is on and is providing me with error code 26. Something about Air-fuel rich malfunction. I took it to my mechanic and they suggested it be the MAF meter, but it was just replaced so I have doubts. I think it may be the cold start fuel injector because the low RPM and roughness of idle only occurs when the motor has been off for a while. I'd appreciate any input I could get.

Here are some pics...


MAF Meter that was replaced...




What I think is the cold fuel injector...




I hope I didn't break any forum rules! Thanks guys.
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Old 01-25-2011, 01:57 AM   #2
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That's not a MAF (Mass Air Flow) sensor. It's a KVAFM (Karmen Vortex Air Flow Meter), but if you need a generic term call it an AFM (Air Flow Meter).

The cold start injector ONLY injects fuel while the ignition is in the start position (while the engine's cranking, unless your ignition switch is broken). ONLY DO THIS IN A WELL VENTILATED AREA: To see if it's flowing fuel when it shouldn't just unbolt it and let it hang down. Put a clear plastic bag over it and tie it on. Clean up ANY amount of fuel which may be present. Now jumper FP and B+ in the diagnostic box (THERE WILL BE SOME LIGHT SPARKS!) this will start the fuel pump... if you see the CSI spray or drip fuel, it's bad.

You should approach this by the book and wallet. Go through the list of suspects and test, then replace the cheapest one that's out of range and move up from there.

  • Injector circuit
  • Injector
  • Fuel line pressure
  • Air flow meter
  • Cold start injector
  • Oxygen sensor circuit
  • Oxygen sensor
  • Water temp sensor
  • ECU

Has the AFM been modified or abused? Did you have the problem since you installed it? Usually when someone posts with trouble from this code it's either a situation where they thought it'd be cool to gut the honeycomb, clean it with carb cleaner, or drop it (BTW, these will all destroy the meter equally well).
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Old 01-25-2011, 02:02 AM   #3
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Check the TPS and its IDL switch and check the ISCV while you're diagnosing things. IDL signal is used in the calculation of that error so it's worth inspecting even though those two components aren't on the TSRM's list.

TPS inspection and calibration:
http://www.cygnusx1.net/Supra/Librar...ction=FI&P=100

ISCV inspection:
http://www.cygnusx1.net/Supra/Librar...ction=FI&P=106
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Old 01-25-2011, 05:09 AM   #4
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Thank you! Would the fact that it's a straight cat be a possibility too? I may just have to change the idle speed... that would be an easy fix, and a great relief. The previous owner had replaced the AFM, so I'm guessing it has no problems. It's mostly stock. Just a aftermarket radiator, MHG, studs, hoses, seals.


P.S. That site is amazing...

Last edited by Fr0sTbY7eX; 01-25-2011 at 05:17 AM.
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Old 01-25-2011, 06:40 AM   #5
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The idle is computer controlled.... screwing with it for the sake of masking a symptom is simply stupid; If you are really running rich you'll still be getting the error code, still be losing power and still be getting worse mileage than normal. Fix it or sell it.
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Old 01-25-2011, 04:27 PM   #6
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Ok, I understand what you mean. Thank you veru much for the time you took to help me, your input is very helpful. No way am i selling it, i just bought it, so im gonna figure it out. Thank you!
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Old 01-25-2011, 06:51 PM   #7
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Sorry for the double post, but I let it crank a little longer this morning and the rpms were just fine, so now I'm wondering if its the straight cat? I dont know much about cars, I apologize if I trouble anyone.
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Old 01-27-2011, 02:15 AM   #8
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Quote:
Originally Posted by cre View Post
Usually when someone posts with trouble from this code it's either a situation where they thought it'd be cool to gut the honeycomb, clean it with carb cleaner, or drop it.
What did you mean when you said "gut the honeycomb"? I know there is no cat on my car...is that the same thing? Sorry for my noobness, I appreciate your help.
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