In trying to troubleshoot my lumpy idle, I noticed that the "lumpiness" exists as I rev the car until about 2k, then it's all smooth. When I hold revs at 1500rpms, I can hear the slight misfire. It's very puzzling since there is no code. A couple of years ago my #1 injector gave up, but in that case the misfire was throughout the rev range. Another mystery is the way the revs seem to hang up around 1k when I coast to a stop...not sure if there's a relation. Here's what I've done/encountered so far:
- Cleaned TB/IACV
- replaced PCV/installed Iridiums & Z32 fuel filter
- got an 0302 code 2 weeks ago, cleaned up port on IM for EGR - no code has returned

Next attempt would be to clean the EGR valve.
Any ideas?

 

Have you checked for exhaust leaks? That can cause the symptoms you describe.

 

Well I had a leak at the muffler flange, got rid of that with a new muffler. I thought that might the issue, but unfortunately not.
It may be the EGR is not closing fully, I tried to spray some cleaner into the bottom of it while it's on the car, but no help. Most likely have to remove it completely and clean it. When the car is idling, I can push up the diaphragm & cause it to stall, so I know the tube is open to the intake. Seems to be a vacuum leak, so I've check all other hoses & they are fine. I think I can hear a very slight backfire as I coast to a stop when the car is cold too.
Only other thing I know is the rear valve cover leaks like crazy, can this be a factor?

 

I never said I didn't. I said I replaced it

I put on a Dynomax Superturbo 1147.

Now back on topic...

 

I had the same problem a year ago...it is a bad coil pack. I didn't get the check engine light or any codes when mine went out. If you don't find the bad one & replace it pretty soon, it will start bucking alot worse when idling (sitting at lights, etc.). People will tell you to replace all 6 of them if one ever goes, but that is really a matter of opinion. I only replaced the bad one and haven't had any problems with any of the others.

 

As an FYI,on the weekend I took out the EGR valve...never swore so much in all my life Anyway. cleaned it up thoroughly, had to use lots of FI cleaner and patience, and tried to put it in, that's when the cussing increased in decibels. The damn large nut wouldn't go one, after a few attempts I took out the EGR valve and saw that it seems I cross-threaded it at some point
So I put it back in...taped the egr pipe onto the EGR and snugged the nut against it (had to go out). I'll have to either replace the EGR or somehow get the thread redone.
BTW..when I was struggling to get the big nut on, I put a little bit of silicone grease on the threads, thinking this would help, could this have caused the the nut to slip & damage the threads?

Anyway, car is idling great now, just have to figure out a way to fix the threads.

 

Two weeks ago, I cleaned out the EGR, EGR tube, TB, replaced the spark plugs and the air filter - the car ran great for a week, and got rid of the EGR code. Still no EGR code, so it must have worked. However, starting last week, I've been getting this shudder while idling at a light. Feels like the car wants to die (like a major misfire), but does not. Only happens when the car is in drive, warmed up, and standing still. Driving me nuts. Any thoughts?