Rough idle - smooths out when I drive (going insane) Options

[97Supra]

I have never found a problem with an engine that I was unable to fix with some moderate thinking.. but with this 1.8L engine I have done the following:

Symptoms:

Car starts VERY FAST. Click vroom. Perfect. Idles 1200 or so to warm up, then drops to what appears to be factory setting around 750 or so. In park, or neutral the engine is vibrating but you don't feel it as bad. The moment you put it in a gear, R or D the entire car shakes to pieces. Touch the gas, and with a load the problem is magically gone until the next stop light... it never stalls. I just failed emissions for HC.. (unburned fuel... which made me think ignition system)


- plugs
- cap
- rotor
- wires
- coolant temp sensor
- egr check
- re-ground everything
- iac clean / check
- vacuum sensor check
- replace all vacuum lines
- checked for leaks anywhere
- set base timing to factory specs
- changed fluids
- changed motor mounts
- unplugged and plugged back in every sensor to no avail
- put on an entirely different distributor
- drained the gas tank and put in all new fuel

.. The only thing I can think of that I did not try is replacing the ignition coil in the distributor, it could be bad.. but the likely hood of both the old and newer distributors coils both being bad is probably slim... I'm going insane.

Now after messing with the TPS my idle wont go below 1,000 or so.. guess I put it back in the wrong position. Oh well, I'll figure that out later but is there anything I'm missing here? I've tried everything I searched google many times I can't even find anything else to check.

fuel pressure? Any ideas....

This post has been edited by 97Supra: Mar 1, 2011 - 7:05 PM

[Special_Edy]

pull all four spark plugs(keep them in order) and closely compare the colors to see if one is rich or lean. Also try a cylinder balance test. With the engine running use a rag to pull the spark plug wires one at a time, the rpms should drop and the engine will run rough. If one cylinder has less of an effect on the idle speed when you pull the plug wire than that is your weak cylinder.
A compression check wouldnt be a bad idea either, they have a loaner one at autozone