Erratic Idle
 

I have a 89 N/A that I just did a head gasket on.
I have verified all of my vacuum lines are hooked up correct, set the TPS per the TSRM and re-verified correct timing twice all the way down to the pulleys.
However the darn thing will not idle. It fluctuates from 1200 to 1600 RPMs in a steady pulse. When I drive the car it appears to be running right under acceleration.
I am getting no codes of any kind when I scan it.
I am at a loss. If anyone has any ideas, throw them my way. I am about to surrender and send her to the graveyard if I cannot fix this issue.
Thanks,
Jim

Check your MAF (Mass Air Flow) Sensor plug on the air intake near the air filter.

I will check the MAF tonight.
A few more things that might help.
There is no difference in operation when I unplug the TPS and the Idle Control Sensor. It is like they serve no purpose.
The idle control sensor does click as stated in the TSRM but I have not done the electronic check yet.

Pull codes...

http://www.toyota-supra.info/forums/...read.php?t=323

I did and I had no codes : )

I c. It sounds like a vacuum leak. Can you hear anything? Check to make sure all the clamps on the intake are tight and it has no holes in it. Did you replace the gaskets on the intake?

When doing routine checks I have forgotten to re-hook up the MAF plug before and it behaves exactly like you describe, reving up then dropping, almost dying then rev up, on and on..... I suspect that a faulty MAF sensor would also cause this same behavior. It is also possible that its only partially plugged in causing it to not throw a code, the manipulation of getting the airfilter back in and clamped can easily unseat the plug. Best check is to unplug it completely, start the car, note any changes in operation, turn off, then plug it in firmly again, to see if that clears the problem. (I never rely on a computer to tell me the problem, it can point you in the right direction but they are not a replacement for real trouble shooting). If the behavior is different with it unplugged you may have another issue, if it is exactly the same and it does not clear up after plugging it back in fully, suspect your MAF wiring or the sensor itself. Look for physical obsrtuction in the sensor too. A pine needle in the wrong place can foul up the readings without throwing a code. The O2 sensor can also have affects here (but slower reacting) as the 2 are working together to optimize your mixture.

A faulty MAF would throw codes. Especially if it was unplugged.

I put all new gaskets on except one. The ICS is on back order but I did silicone it very thoroughly.
I have sprayed starter fluid around every possible area of potential leaks and it does not change at all !!!

No codes, no leaks. I'm stumped my good man. Spark problem maybe? No clue now, lol. Good luck.

Beyond the afore mentioned checks, yes vacuum leaks can behave this way too, also check that all plugs are firing consistantly, an inductive timing light w/ RPM reading works good for this. Clamp onto each plug wire, and check that the RPM/Flash rate is consistant with the Tach. Try to listen for a solenoid switching when the rev changes, there are 2 of these guys under the intake that are almost identical and easily mixed up when hooking the vacuum lines back up. I would have to check my shop manual for the correct hookup.

I did install a new O2 sensor to a universal type (1 wire)
Could this be a possible cause?

If you have a vacuum guage (you can buy one from a parts store for about 20 bucks) hook it up on the hose that goes to the cruise control and see how it reads and let us know if steadily rises with the RPM or is really ratchety and what the reading is.

I did notice there is no VTV on the dash pot anymore.

Could this cause erratic idle?
I also have a crack on the bottom of the air intake after the MAF sensor.
It does not register as a leak when I do the spray check.
Still messin with this thing : (
Any body wanna buy a nice Supra "CHEAP" ?????????

I would definately try to seal the air leak, I am not familiar with this 'spray test' but if it is leaking, after passage through the MAF Sensor, that is equivalent to a vacuum leak, as far as the computer goes (getting more air flow than is being measured). Do what you can to minimize or eliminate this leak.

Additionally I would suspect the O2 Sensor conversion, if memory serves correct the second wire is just a shield wire, but the operational parameters may not be the same as the stock sensor, and EMI may affect is performance (purpose of the shielding wire). These enignes are heavily reliant upon computer control, everything is manged by computer, including spark timing. You can actually adjust the Cam position sensor out of proper position and the computer will actually try to compensate, and bring the timing back in.

This is also a point you my want to double check. Did you check and adjust your timing with the auto advance turned off? The are 2 connections on the diagnostic plug that you have to short when setting your timing (Cam position sensor). This must be done prior to starting the engine, to prevent the auto compensation. On a typical older car this is the vacuum advance on the distibutor you would plug, but the Supra is all electronic timing, you have to short the proper connection, again I would need to consult my manual, but it should be documented in every manual specific to this engine.

I did not short sensor when I set timing.
This one is an N/A so there is no CPS but the leak does make since.
It happened when my engine was being re-built so it is a new condition.
Thanks....

Can someone tell me how to pull codes from my car??? Can I do this myself or does it do it itself ? Do I need a diagnostics computer?

I'm curious because I have never seen my ride throw any thing close to a code other than the bird cage light, lol. We all know what that one is.

Thanks.

Ya, it real easy.
Start here..

http://www.cygnusx1.net/Supra/Librar...ection=FI&P=23

Thanks alot. Highly appreciative.