1998 Pontiac Sunfire rough idle

GILBY213

MEMBER
1998 PONTIAC SUNFIRE
4 CYL
FWD
MANUAL
124,000 MILES

I just replaced my O2 sensors, front and rear on my 98 sunfire 2.2L. Now when the rpms get low (e.G when Im slowing down, or about to park, ar starting out in 1st gear) the idle gets rough and it nearly stalls.

I checked the codes (cuz my check engine light was on) before I replaced the O2@ sensors and it said that the front one had "low activity" and something about the timing being off.

So I replaced the senors, then had the codes deleted and checked them again and everythign was ok. Then the check engine light went off and that was that. I even replaced the air filter, spark plugs, and wires. I dont know how the timing could be off in the first place since the computer controls that (unless maybe the timing belt is stretched, but I dunno). The car runs great and only gets the rough idle when im at low rpms. It never did this until I replaced the sensors. Any help?

1 Reply

MERLIN2021

MECHANIC
17,250 POSTS

If you have no codes now: You may have a vacuum leak, get a can of spray gumout, spray the vac lines and maniflod area, when the idle changes, youve found the leak! You want the engine running and spray on the outside but do direct the stream onto the hoses, if it is a vacuum leak, the engine idle will change speed, then you have detected a leak, repair the vacuum leak and see how it runs! If no leaks found, check the idle air control motor, and the EGR for any carbon holding it open.