I have a 1998 A4 2.8, and just changed my timing belt, I had the mechanic change it (friend of mine). So i got the car back and when i first start it up it sounds really loud, almost like a deisel engine. After it runs for about a minute the noise goes away and almost sounds ok. The best way i can explain it is that it sounds like someone is revving it for about a minute, then after that it sounds like the gas was let go, and it sounds a little better (engine still runs a little loud though). I brought it back to the mechanic and he told me that everything was timed perfectly and that he does not know what could be the cause of this. So i was wondering if maybe anyone here has ever heard of this problem, and could maybe help me out? I appreciate any help you guys might be able to give me. Thank you

 

Vacuum leak? Sensor not plugged in? Are the revs actually high or is it just the noise?

 

no the engine does not rev, but it sounds as if it is revving. After a minute or so, it sounds somewhat normal. I say somewhat because it still sounds a little loud, at least to me anyway, maybe these engines run loud? I do get a check engine light, but that is due to a different problem, secondary airflow... can't remember what it is exactly. I don't think these two are related, but maybe they are? Thank you for your responses, hopefully i can get this thing figured out.

 

probably secondary air pump -incorrect flow detected. that is not a related problem.

what kind of oil have you been putting in the car?

 

I had the same code and eventually found that the vacuum line connected to the egr valve was bad. I replaced all the vacuum lines and cleared the code and the cel never came back. The engine sounds different now at a cold start. Before the problem, the secondary air pump had no back pressure and sounded like there was a shop vac inside my engine bay.

 

i have been using synthetic motor oil.

A4 2000, now that you say that, maybe that's my problem as well? That might be what i am hearing right now, after about one minute it stops making that noise though. I have been trying to correct this problem for a while now, and can't seem to find the cause of it. I believe the egr valve is located in the back of the engine am i correct? I think i remember changing that hose, but i can always double check, i thought it was the egr valve itself and have been putting it off, simply because it looks like it's complicated to get to.

 

Yeah, it's that shiny metal valve behind the head. Double check the line that connects to it. While you're at it, it wouldn't be a bad idea to get a flashlight and check all of them. One thing to remember is that the code won't clear by itself after driving for a while. I had to clear it with my scan tool. If that doesn't fix the problem, then there's a chance that maybe your secondary air pump is going bad.

 

just one more thing to add before i go under the hood to see what i can do, when i replaced some of the hoses and cleared the light, i thought i might have fixed it, because it hadn't come back on for a good month or so. Does that mean that it might just be a small leak somewhere or is that just how long it took the car to go through the cycle to check for any problems? It seems to do it more in the cold weather by the way.

 

My egr valve almost fell off my car ! and it was a bitch to put back on. Its probably easier to remove the bracket that it attaches too. You can check to see if it works by applying vacuum to it.

 

And if it doesn't work, you can try cleaning it out with like carb cleaner. Preferrably while off the car, of course.