Jon Hekking

My 94 has developed a new habit, not sure what to think. When it's cold it idles a little rough but barely noticeable. Lately, after it runs for a while, maybe 10 to 15 mins, the idle gets a quick surge and it becomes smooth as glass. When this happens the "service soon" light comes on. OK, hook it up and pull the codes...................no codes. It goes off again after a while as well. It would seem the ECU is detecting an issue and adjusting, like a lean condition (my first thought) so maybe an O2 sensor. I had a good friend here recommend pull vacuum in both conditions, haven't gotten to that yet. It still runs just fine, no other issues.

It's going if for it's annual emission testing tomorrow, hope this doesn't cause a problem. Anyone have an idea where to start?

Tom400CFI

I'd probably throw a scan tool on it, see if the surge occurs when it goes into closed loop.

I'd probably inspect the IAC & TB for cleanliness...maybe confirm CTS is reading correctly...

Jon Hekking

OK, vacuum unchanged under both conditions.

antfarmer2

O2 sensors get tierd and don't alway put a code out I put the two front ones on my 94 what a differance

WW7

Jon, I agree with Tom, hook it up to a scanner.. Most times a scanner will show you where the problem is occurring..This is usually the first thing I do when a car starts acting up......WW

Jon Hekking

Got it on a scanner today and the winner is...........................

Bad O2 sensor. ECU reading lean condition, correcting and throwing it into a closed loop.

antfarmer2

what did I win?


You will need the short o2 wrench oriely's will loan it for $20 deposit or sell it for $25

Tom400CFI

Nice work.

Jon Hekking

So I left the Vette with a friend at his GM authorized, AC Delco repair facility to replace the O2 sensors and let him "play" with the tune up. I picked it up today and holy crap what a difference a couple of O2 sensors make! This thing runs like a ra......, I mean violated ape. Hard to believe it's the same car. I also had him take the 10 year old Michelin Pilots off, even though they had plenty of tread left. He put on a set of Goodrich G-Force 2 comps on it, great looking and feeling tire.

A very pleasant outcome.

antfarmer2

Frizlefrak

O2 sensors are consumables and need to be replaced every so often. And like yours, they don't always send any more of a distress signal than you got. Glad it's fixed.