| Got a 96 NA 5spd 88k miles, no mods. Been chasing a rough idle for a while now. So far I've gone through all the FSM procedures for a rough idle and it all checks out. Harnesses are original and in great shape
Compression is good, 205-210 all 6
All injectors OHM correct and are working
Power balance OK
New IACV and regulator
New TPS set correctly
Zero vacuum leaks
New spark plugs
Ignition timing set correctly
New fuel / Air filters
O2 sensors cycling between rich and lean at 2k RPM
No codes
Tried a second good working ECU, problem unchanged
Close throttle pos. switch is ON during idle
New PCV valves and hoses
Throttle bodies are in sync and haven't been touched Idle set to factory 750, I can see the ignition timing in conzult and on the crank pulley jumping around from 4 to 10 deg BTDC. The engine is very shaky and the whole car vibrates heavily. The RPMs are fluctuating around 100-200 RPM. The exhaust note stumbles, sounds like its missing or a bad vacuum leak, but those have been ruled out. With TPS disconnected, at 750 RPM, ignition timing is steady at 10 deg BTDC and the engine is smooth. RPMs stay steady. Plug the TPS back in and it immediately returns to the rough idle. The only way I can have a "smooth" (but not as smooth as TPS disconnected) idle is to dial the IACV idle screw all the way out to inflate the idle RPM to 950-1000, at which point in conzult the ECU has ignition timing at 0 deg BTDC and it shows the same on the timing marks. Also, with idle set anywhere above 750 RPM when moving from neutral into any gear I can see in conzult the ignition timing jumps from 4-10 (or 0) deg BTDC to a steady 10 deg BTDC and the engine smooths out but for whatever reason the idle RPMs jump by 500 up to about 1200-1500 RPM. Move back into neutral and RPMs drop to where they were set and the ignition timing goes back to dancing around or staying steady at 0 if I have RPMs set around 950-1000. I am looking at replacing both up steam and down steam O2 sensors, trying a different MAF, and replacing the flywheel sensor on the side of the transmission. ???
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