CEL came on with a lumpy idle - what is the culprit?
 

I have just returned home from my 1200km trip from Vancouver to Calgary, but about half way home, the dreaded CEL came on. There was no obvious changes with the check engine light coming on, but one thing I noticed was that when I came down from highway speeds, the car had a bit of a tough time keeping a steady idle. It would blob up and down perhaps between 500 and 900, intermittently.

I do know that the car did not do this before the trip. I do not know if it has anything to do with the check engine light.

Before I take my car to the dealership to have them diagnose it, I'd love to hear from anyone who wants to take a stab at what the problem might be.

One thing I thought it could be was that one of the o2 sensors is getting to the failure point, and with all the highway driving I Was doing, it just gave a bad reading for a short time, thus triggering the CEL. Does the emissions CEL automatically go out if it corrects itself (Like for BMW), or once on, does it stay on until cleared? Of course this would not be related to the idle issue.

Another thought I had was that some vac line somewhere has become crusty and cracked.

Any other thoughts are welcome!

Please read the error code (OBD-II) associated with the CEL and post it here.

Just as an update, I purchased the durametric so I will read the codes in a week's time.

A further observation of whatever the issue may be is the following:
There is absolutely a relative loss of power when cold, which is especially noticeable in lower gears. As the car warms up, the loss in power seems to become less apparent, but may or may not go away altogether. Reading diagnostic codes will be interesting.

Car still has a lumpy idle when warm. Perhaps pulsating is a better word for it. It'll go up 50 rpms and down 50 rpms every 2 seconds at a regular interval. Maybe it is a bad O2 sensor preventing the car from going into closed loop mode properly.

I'll venture to guess that the cel reads out as being code P0102 .

YOU ARE WINNER

Just read out 1 fault code: P0102

lol. And I cleaned my MAF a number of times.. Looks like a new MAF is in store for me.

So for future reference, lumpy idle, loss of power + CEL light on MAY equal needing a new MAF for you!