here is my problem... my car starts up fine, and runs fine until it goes into a closed loop... but when it goes to closed loop the idle is terrible... it jumps anywhere from 200-300 RPMs... i think it is something igition wise... possibly a fouled plug or something... i just changed cap, rotor, and plug wires... so those aren't the problems... i went to the track last weekend and it has been running like this since... and when it idles bad... it makes an almost knockin noise i can hear from the tailpipes... i have a valve seal problem, which may be covering the plugs with oil... but i dunno what else it could be... any other ideas? thx in advance

chris

 

Does it run alright above 1500 to 2000 rpm? I just recently had a problem with my vortec V-6 blazer engine. Wouldn't idle for beans. With the OBDII system they SES light came on at start up. Checked it out and it was the EGR valve. I would think the older system in the camaros would also light the SES light up. My 86 IROC did (even though it ran and idled fine) due to a very low restriction exhaust system. If the EGR valve is open too far at idle the engine will miss and you'll think you've got fouled plugs as you can smell the gas from the tailpipes.

 

yeah... i will look into the egr thing... cause it is really making me mad now... i gotta find out what it is!!

 

Its not ignition related becauce it is not computer controlled so it would happen all the time. I would change you o2 sensor being a sensor not used in open loop.

 

Chris,
I've been battling a similar problem for some time. When it warms up, the idle will drop and then it will surge to 800 and back down to 650 and up and down. Not all the time, but often enough.

I checked everything. I disconnected the IAC. It still hunted. I disconnected the set timing connector. IT still hunteded. I disconnected the IAC and timing connector. It still hunted. I disconnected the MAF ... it ran crappy but still hunted.

Lately I did a test. I disconnected the O2. The surge got WORST! IT hunted from 500 to 1000 RPM.

I suspect when the engine goes into closed loop, it uses the O2 for input. Perhaps my O2 is sluggish and the engine will rev up and down too much before the O2 responds?

My scanner shows a reading from the O2. It shows closed loop. I have cross counts. It does not look like anything is wrong.

But since unplugging the O2 was the only thing that made a difference, I am temped to replace it.


If you can get at yours, warm up the engine until it is closed loop. Then un plug the O2 and see what happens. It won't set a code, rather the ECM goes to some odd mode where it "thinks" the O2 is there and is getting 450mv reading. IT only will have the RPM to use to determine if it is metering the fuel properly at idle.

I have not replace my O2 yet. It's on the list of things, but with school starting, I am broke.

Mark.
PS. do a search on idle surge and you will find my long winded testing procedures for my idle problem. Might give you some ideas.

 

I was just about to post the same problem! Runs fine in open loop. Actually it stays in open loop for the most part. When it does finally go into closed loop it runs like crap. Runs rich in open and then goes lean in closed loop. O2 sensor is pretty new and seems to be working according to the scanner. I was messing with my fuel pressure when this started happening, because I was supposed to smog it today, now it's going on a non-op. Fuel pressure is set back where it was now.