Ok I just got a 02 z28 a4 not too long ago. All has been good so far until today...
I got in the car and drove to work no problem. I was sitting at a stop light on the way home and noticed that it was idling around 5-600 rpms and felt kinda rough. The SES light came on right before I pulled in the driveway. What's most likely the culprit? I guess I'll have the code scanned tomorrow and see if I can track it down. Just wondering if anybody has had a similar problem( I'm sure somebody has). Oh and btw sorry for such a noob question it's just bugging the hell out of me right now. Thanks.

 

was the light flashing

 

Could be a variety of things, maf, o2 sensor,bad coil or plug etc. Get the code scanned but more than likely and oxygen sensor has taken a crap imo.

 

What he said a flshing ses light is a misfire ie. coil or something ignition related

 

Oh yeah forgot to post that the light just stays on. It does not blink. I'm glad it's not that I saw in some other posts that the blinking ses is a engine misfire. I'll post up tomorrow see what I can come up with.

 

It can still be a misfire without flashing, but flashing means a severe misfire.

FYI, sounds like your idle rpm is right where it should be. Stock idle speeds for all LS1s '98-'02 are as follows:

A4: 650rpm in P/N, 550rpm in gear
M6: 800rpm

 

Get the code read at autozone. They will tell you what the problem may be. My car always idles at 500-600 RPM even when it was Misfiring severly(SES light flashing) last friday it was at the same RPMs just vibrating alot...and when i would giv it a quick rev it wanted to cut out...Went to the gas station and filled up and idk y but the misfire was gone...either solved the problem or it was just coincidence and the misfire might come back later. Car is running good right now though.

 

My car was throwing P0357(Coil malfuntioning) and P0300(Random misfire) and my reader said Cylinder 7.

 

Ok the code is the catalyst system below efficiency. Of course, I don't wanna replace the cat or cats bc I planned on doing long tubes in a month with my bonus check. ****, hopefully it's just a 02 sensor? Damn..

 

Btw the way thanks guys for everybody's input. Maybe I can get some help tracking it down. The car is stock other than intake/exhaust. Just hit 100k miles.

 

there was a recall on these cars for cats plugging up, that could be the issue

 

Never heard of a post cat 02 causing a rough idle. I'd also put my money on a plugged cat...

 

I cleared the code and it's running fine now..If it comes back it's probably the cat. Oh well I need long tubes any way and a good friend of mine is a tuner here in Alabama. That's a good reason to mod huh? lol.

 

I've been through this a bunch of times with several different types of cars. It's usually not the cat. Most likely culprit is the o2 sensor (probably the rear or post cat) or a vacuum leak. Since you cleared the code and it's running good the cat should not be plugged up. Good Luck

 

your tuner can turn off the parameters for the rear o2 sensors so you wont have to worry about them anymore

 

I heard about this too. And I also heard that if it is due to the cats and there is a recall you can go to the GM dealer and possibly get them replaced free of charge. Theres no harm in driving over there and asking them. Good luck.

 

Yeah I believe the post cat driver side 02 sensor is the culprit. Yeah I'm going to get my tuner to turn those off after I get long tubes. Running fine today turned over the tires going into second today and it's an A4 lol. I love this car damn!

 

Ok turns out it's the driver side cat is plugged. Gm said I was good on time but my mileage is over...uggggghhhh! just hit a 100k. They said the cats are only cover for 8 years or 80k miles...

 

Do you have a visual or sniff test in your state? If not, ditch those cats and never look back. If you have an OBD scan test, any good custom tuner can fix you up to still pass that test without cats....or you can use O2 sims.

 

ditch the cats!