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

[97Supra]

got the car back, it passed inspection and the shop couldn't figure out what was wrong.. all the owner .. a tech of 30+ years could say was:

"Adjust the hard idle setting with the screw, and change the motor mounts."

I already DID change the hard idle and somehow no matter how high I put it, it wont idle higher than like 700 with it way out where 1,000 should be and the mounts aren't causing the needle to fluctuate. When I start the car, the car is searching for an idle speed that it's hardly able to steady.. it doesnt jump a lot, but it fluctuates 200 rpms at least up and down for a few seconds and sometimes at lights it dips too far, or raises without throttle input. It's like a vacuum leak but I retorqued the manifold gasket, and sprayed carb cleaner all over the engine.. the rpms didnt change and I was using a timing light so I'd have a dead accurate reading of the rpms.

I have a set of cleaned up injectors I'm going to install with new rubbers, and I'll change the intake manifold gasket with a brand new one. If the new gasket doesn't have any impact, I'm going to probably give up.. I already have the gasket so I might as well.