I have a 94 z28 a4 with 67k on it and recently when it is in the RPM range of 1500-2000 the car chugs and shakes like it is running on full power then not and this goes on only for the range above. Other than that the car performs perfectly. I have a MSD coil, MSD wires, Delco plugs gapped at 50, K&N CAI,New Vechile Speed Sensor, new Fuel Filter, cleaned throttle body, checked egr and a orginal opti. This is noticed in all gears but mostly in 4th when the RPM range is so long, also when going up hills it is noticed the most. Please advise Thanks Robert

 

engine chug or driveline chug?

 

When my car stumbled in that same rpm range the problem was the opti. I did a vented opti conversion with my cam swap and the problem went away.

You have a nonvented opti just like I did, and they are more prone to failure then the vented ones.

 

Is it just when you're at part throttle or all of time, including WOT?

If it's just at part throttle, it could be O2 sensors.

 

The EGR functions at those rpms under medium to high load conditions like you describe. I see where you checked it. Have you had it scanned? Could be you're getting a DTC but no SES light. Not sure about the last sentence.

 

I had the same symptoms this fall. Performance was fine, but apply the throttle much at 1500-2000, and it would stumble and buck. Above that it was great. I'm doing a heads/cam swap now and when I got the opti off, I could hear pieces rattling inside. I'm pretty sure it was the opti causing the problem, but I'm surprised it was still running at all.

 

I had a similar problem and a new EGR valve fixed it.

 

i have the same problem and can not figure it out. the car is not missing or anything. just between 1500 and 2000 there is a little lungeing going on. i checked on getting a new egr valve and i found out they are like $75 to $100. i am not going out and buying one if that is not the problem. if that is the problem then i will get one. i don't think i will be able to change it anyways. that thing is tucked so far back there it is not funny. i am not getting a ses light. but my check guages light is half way illuminated. i figure there is a bad ground/connection somewhere. if i figure it out i will let you know. i have a vented opti in my 95 so i don't know if that is the problem or not.

 

I've heard many guys in the US tell me that the EGR valve is only about $40. I only paid $60CDN up here with my car club discount.

 

Get it scanned at a dealership and check the O2's, they should both read about 450 whatever the measurement is. I replaced my opti twice when it turned out it was an O2, much cheaper

 

I think I have it figured when I was poking around my engine I found that the water pump is leaking through the weap hole anf it might be leaking on the opti! No SES light is comong up so I think this could be it.

 

just wanted to know if any fixed this problem yet? i have the same problem and can not get it figured out. the car is not missing at any rpm.

 

Cals400ex, definitely get your O2s checked out if you havent yet. I had this problem and assumed it was the opti, spent like $300 tryin to fix the problem, and it was a $32 O2 sensor and took 2 minutes to replace. Even if its not the prob its worth getting checked out. One way to know is if you get horrible gas mileage, if your exhaust smells like gas a lot, and if when the car is warm and you rev it, if the cat starts glowing the car is running very rich. Just my .02

 

yeah i will have to get the o2's checked out. how many o2's are on these cars and does anyone have pics of where their located? it is a 95 z. i thought a lean condition would make the exhaust hot and glow but maybe not.

 

Im not positive, it could be lean, one way or the other.
Mine has 2 but its a 94, if yours is OBD2 I think it has 3 or 4, but again im no expert, could be wrong.