My 2000 X308 (NA) is occasionally misfiring while at idle only when in drive with the AC on. It is not showing any codes(yet), restricted performance or check engine light. I have inspected and do not hear or see an obvious break to the vacuum lines but have not smoke tested. Should I just drive until it throws some codes? I will also note that the car sometimes experiences longer than normal crank times when cold perhaps they are related. I would love some ideas.

 

You could watch live data e.g. ECT, IAT, fuel trims in case something is out but not enough out to flag codes.

Also see if you have P1111 as you should (else P1000).

Don't clear the codes! You also clear the OBD monitors and then most codes can't flag.

 

Misfiring under load at low rpm points to a spark plug or coil issue. John's suggestion
of watching the live data is good as it may allow you to identify the cylinder/s that
is/are not behaving as they should. It's not always coils or spark plugs but that would
seem to be the best starting point.

 

Thanks for the replies in the past when I had a coil go bad it was a much worse misfire and it showed the cylinder code. All the plugs have been replaced although about 25,000 miles ago now maybe it is time... The coils have only been replaced as they have gone bad. John I do have P1000 but no other codes showing. Unfortunately, I just have a cheap scanner so will need to borrow a friends. I will let you know what I find out.

 

I had that problem on one of my cars. Was a weak coil. Just changed them one at a time until I found the faulty one. It would only happen at idle if the car was in drive with the brake on and it never threw a code. I would replace a coil, start the car, pull the handbrake tight, move the shifter to drive and wait about 5-15 minutes. If it did that short stumble, turn off and repeat until the bad one was found. Good luck!

 

There may even be pending codes which don't occur enough in the same way to flag. Worth checking.

 

Interesting, I have almost the identical issue on my 01. Runs ruff at Idle for about a minute then returns to normal but only does this after sitting for a few days. I’ll check a few of the items mentioned but honestly I’ve been putting up with it. Took her on a 1800 mile trip last summer and no issues other than me complaining about high fuel prices.

 

Quick note - P1000 means at least one OBD monitor hasn't set. Each unset monitor means a lot of codes can't flag so you may or may not get much help via codes.

OBD can show which monitors are unset which at least can be a small hint as to what kinds of things may be wacky.