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]

did the fuel filter when we pulled the motor..

Just got back inside just replaced the alternator with a new new new unit, still idles just as bad as before..

so i adjusted the idle stop screw to set it higher since it idles constantly at 650-700 at most .. and that did nothing at all. I'm starting to think there is an internal failure such as a burned valve or something of that nature because the engine was pulled from a vehicle (unbeknownst to me having this idle issue) I have since replaced absolutely every sensor and everything on the exterior of the engine and not a single thing has made any impact on the rough idle or idle speed what-so-ever.

intake manifold / throttle body / all sensors / exhaust with cat complete / intake / entire fuel rail, injectors, pressure regulator, EGR valve, all vacuum hoses, PS pump, alternator, belts, distributor, entire tune up including fuel filter cap rotor wires plugs, new grounds all over, double grounded battery cable, new terminals, set timing, fresh fluids, changed motor mounts... I forget what else

This has been a tremendous waste of money thus far and I'm just going to have to pull the plug on searching for now, it's going to be looked at by a mechanic my father uses so we'll see what they have to say. If they can not figure it out either, I'm just going to make sure it passes inspection and drive it into the ground. I have an MR2 turbo I waste all my money on, this cars eating up too much. I'll post back with results from the shop in a week or so.