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.