idles rough in drive at a stop, smooths out in neutral or driving. compression test all cylinders pretty much the same no vacuum leaks that I can find. no codes. please help. not a huge deal just not right
What was the compression ?
Just because they’re equal doesn’t mean it’s good.
The compression is at 165 psi give or take 2-3. I didn’t mention its pretty smooth cold then after warming up to temp is when the rough idle in drive starts.
That would imply drag in the transmission. Do RPMs drop along with the rough idle? What if you are in D, foot on brake, and give it just enough gas pedal to raise the RPM a bit?
Smooth idle when cold but rough idle when warm points to your original suspect - vacuum leak. Those can be really tough to find. Did you spray something flammable around the intake manifold to verify that it is not an intake manifold gasket leak? Next would be disconnecting each of the vacuum hoses from the manifold one at a time and plugging their ports temporarily.
Does this car have an idle air control valve? I would get some aerosol cleaner and clean the throttle body and the IAC valve (if any). I would also clean the mass airflow sensor.
I have a 92 Corolla w/4afe engine. If you also have the 4afe engine, suggest to do the basic stuff first; i.e. make sure the idle rpm and ignition timing are to spec. The 4afe uses a manually adjustable idle air bleed screw to allow you to set the idle rpm. It must be set to spec (800 rpm, warm engine on mine) otherwise the engine will never run correctly. Good idea to check the throttle position switch at the same time. If all that doesn’t do the job, since it idles better cold, some kind of lean mixture or misfire problem when warm I expect. Might try a basic tune-up: Replacing the spark plugs, distributor cap, ignition rotor, and spark plug wires is worth a shot. Checking the valve clearances is a good idea too. The 4afe has a sort of idle air control gadget, but it is activated by the coolant temperature. It can’t be serviced or cleaned in any simple way. If that part failed it would show up more when the engine is cold than warm. So I doubt that’s the problem. There’s plenty of ways unmetered air can be getting into the engine and cause this, so check the obvious ones at least: the air boot from the air filter box to the throttle body, the canister purge valve (looks like a vacuum valve that screws into coolant jacket), the vacuum switching valve at the end of the passenger side top of the engine, the fuel pressure regulator, power steering pump vacuum switch, the MAP sensor (the 4afe has no MAF sensor), and the power brake booster. An EGR problem could cause this too, but less likely than the above imo.
If you feel lucky, spray some starter fluid around the engine compartment. If the idle improves at one particular spot you’ve probably found the problem. Also you could try some fuel injector cleaner. One time my Corolla started to lurch going around corners during slow speed neighbor driving. It seemed like it would either want to go too fast, or wouldn’t go at all, depending on how much I pressed the gas pedal. That turned out to be caused by dirty fuel injectors. Best of luck.