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94 Racing at idle


jerryls
10-20-2007, 07:30 PM
My 94 with 156K miles races when started, probably around 2000 RPM. It's worse when cold. When hot it still idles high, but not as high. Any ideas on what what would cause this? Also, I'm thinking the mixture is rich, because the car smells like it's burning up? It could be two different problems.
Thanks

maxwedge
10-20-2007, 08:22 PM
I'd scan the pcm to check the coolant temp sensor inputs, also clean the iac, passages and throttle body.

jerryls
10-22-2007, 11:54 AM
I wish I could scan it. The 94 had an OBD1+ computer. I have an OBD II scanner that will not read it. Autozone said they can't read it. The dealer wants to charge me $80 just to read it.
Anyhow, what is the IAC?

jerryls
10-22-2007, 01:59 PM
I'll check the Idle Air Control, test and clean.

jerryls
10-25-2007, 10:21 PM
We'll cleaning the IAC did nothing. The car will drive down a level street at 30-40mph without my foot on the gas! I'm about to find a good cliff, put it in gear, and jump out! I would not have to put a brick on the accelerater as they do in the movies.!
This car is extremely frustrating. It took a long time to fix the intermittant stalling problem. it turned out to be the MAF sensor. Thanks to this forum! .Could it be a bad TPC. Can I test that with an ohm meter? The Autozone repair guide says to check the ouput with the ignition on, but I can't easily get at the pins when the connector is plugged in. What else would cause this?
Thanks

maxwedge
10-26-2007, 04:36 PM
Tps or bad iac, binding throttle plates in the TB, bad coolant temp sensor sending cold temp info to the pcm are some possibilities. You may need professional help if here if you cannot solve this, a full scan, again, may be the answer.

jerryls
10-26-2007, 04:54 PM
I can't imagine a cold engine would require 2-3000 RPM's. but I can check the temp sensors easily. Does anyone know what the TPS resistance is supposed to be? Mine reads about 490K which I think is probably too high.There is no SES light ever coming on.

HotZ28
10-26-2007, 07:31 PM
The TPS uses a spring return and you need to check that first. Put your finger on the TPS lever and move it all the way to the open position. Now, let go of the lever and it should return to the home position quickly. If not, the spring is broken and you need to replace the TPS.

The TPS is simply a potentiometer used to vary voltage. The best way to check the voltage is with a scanner, but if you do not have access to one, you can use a DVOM. You can probe the terminal with a paper clip to check voltage. The TPS WHITE wire, is the PCM reference signal and should measure 5.0v with ignition on. (Engine does not need to be running) The BLUE wire will show variable voltage from a closed TB position, usually .45v, up to WOT, where it should measure between 4.0v to 4.2v max. The BLACK wire is ground.

In order to verify the voltage that the PCM is interrupting, you must use a scanner. I have seen several throttle position sensors check fine with the volt-meter; however, the PCM was interrupting the reading different! In this case, the reference voltage from the PCM was correct (.5v) and the PCM was at fault.

jerryls
10-27-2007, 11:54 AM
Thanks HotZ28. I appreciate your information. You are one of the best sources of information on this forum. I'll check out the TPS as soon as it stops raining!

jerryls
11-26-2007, 03:20 PM
It turned out to be the TPS. I replaced it and the car now runs fine. BTW the new TPS has a resistance value of about 5000 ohms. across it and the pointer varies between that depending on position. My old one read about 3-5Meg, so I think it was basically an open circuit.

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