Idle Surge, Runs Rough when warm

[gage]

89 IROC 350 TPI, idle surging up and down after coming to a stop light. Only does it when engine is warm (not necessarily all the way warmed up). That was the only symptom for last few mos...now it is starting to shake a bit at idle, and the exhaust note sounds different, louder not as smooth. you can also feel it surging a little bit when cruising in 3rd/4th gear around 45 mph. Also a strange sour fuel/unburned fuel smell after you shut it down. When you get on it still has good power though.

Checked ECM, no stored codes, no ck eng light. Any ideas?

[Trash man]

is that a speed density or Mass air flow car?

[gage]

Mass air flow

[Joe 1320]

Almost sounds like the oxygen sensor(s) cross count is getting sluggish. It would be interesting to see the 02 millivolts in real time.

[gage]

Almost sounds like the oxygen sensor(s) cross count is getting sluggish. It would be interesting to see the 02 millivolts in real time.

Wouldn't it throw a code for the O2 sensor?

[Joe 1320]

Not until the sensor gets bad enough. There could be lots of issues. Reading the o2 counts would rule out the sensor, you could have vacuum leaks, weak spark, a whole host of issues. You'll need to systematiclly eliminate possible causes one by one.

Check for vacuum leaks, check plugs and wires, MAF, etc.

The unburned fuel smell leads me to believe either a false lean condition read by the computer or weak ignition. The part where is changes once it wams up makes me believe it's a sensor issue that comes into play when the computer goes into closed loop.

[gage]

Last tuneup was 50k ago and in 2001 so this weekend I'm going to do new plugs, cap&rotor...new coil for good measure as well. Go from there.

[formula_gramps]

Gage,

As usual, I think Joe is right on the money.....

What you are describing is exactly what was happening to my 94 Formula.

I changed a lot of things, plugs, wires, etc. and the problem was still there.

Changed the two O2 sensors and I had my bird back in true form.

Mine never threw any kind of code. But it ran like crap when it was warmed up. Smooth as silk when it ran in open loop. Now I have a scanner and would be able to see the sensor voltages if that ever happened again. Hopefully, if you change yours out that'll fix it. I also hope yours are easier to get at than the one on the passenger side manifold of my car.
The thing was practically welded in there, so I wanted to use all 1/2" drive. I had enough universals, extensions, etc. to build a *bad word* bridge, by the time I was done.

Good luck!

[gage]

guy at the Auto parts counter used to own a 92 Camaro Z28. He recommended a new coolant temp sensor for the problem. Installed it, car barely starts, then it barely runs....WTF!!!put old sensor back in, fires right up, runs better, but still running rough and same issue(s) as before...

[gage]

threw code 13 on the way to the auto parts store!! Hooray, off to the garage to replace O2 sensor!!

[FTA1995]

guy at the Auto parts counter used to own a 92 Camaro Z28. He recommended a new coolant temp sensor for the problem. Installed it, car barely starts, then it barely runs....WTF!!!put old sensor back in, fires right up, runs better, but still running rough and same issue(s) as before...

That's interesting.

I'm having some issues like you described to open the thread, only my idle will still surge a bit coming to a stop even in forced open loop.

Hope your problem works its way out.