I have a 1996 Audi A4 2.8 12v. I love my car. Ever since I have had the car, it has had a slightly rough idle, and it stumbles and shakes a bit when accelerating. It also feels a little weak for a car that is supposed to have 172hp. It mostly does it when taking off from a start or when accelerating at low RPMs. I have replaced the wires, plugs, air filter, fuel filter, vacuum lines, and nothing has improved the problem. There is no CEL, and never has been one. I gave up eventually, and took it in to the Audi stealership a few months ago, and they told me I needed a new coil pack and the ignition control unit. They said they could fix it for $1100. I told them to give me my car back. I didn't think this was the problem, as that would cause a misfire in my mind, which would have given me a CEL. I drive 60 miles one way to work, so I am sure if it misfired, the ECU would have caught it, or I would have felt it. I have been driving it like this since then, but would really like to have it fixed, as I think my car would drive AWESOME if it had all of its power. I have a VAG-COM. Does anyone know if there is anything else I should be looking at? I am now thinking about actually going ahead and buying the coil packs and ignition control unit.... since I have no other diagnosis except for what the Audi dealership told me, even though I kind of doubt it. I am wondering if anyone else with this car has had any similar problems, and if they can guide me in the right direction. Or... If the coil pack/ICU thing is actually a possibility? Any help is GREATLY appreciated!!

 

You've already covered the logical points. Try a three-part Seafoam treatment (fuel, oil, and vacuum - the Search feature will turn up the procedures) and see if that helps. Also take off the hardpipe between the MAF and throttle body and clean that and the throttle body itself, since excess crap in there can create this kind of problem. If those don't do it, order a set of valve cover gaskets and pull the valve covers off. On the bottom side of your covers there are metal filtration grates. These are for the PCV system. They can clog up. Take them off (pay attention to their orientation), soak them in a bowl of Seafoam, and then scrub them with a wire brush before drying and reassembling. Last, inspect the square corrugated PCV hose that runs from the valve cover fittings and across the front of the motor. It's known to become brittle and crack. Seal any cracks with electrical tape, and try the car out again.

 

On my wife's old 12v, there was also a feeling of low power and occasional stumbling and it turned out to be clogged catalytic converters. Strangely, I didn't get any codes, just crappy performance. Might be worth checking into if all else is exhausted.

 

Thanks guys. I will Seafoam it this week. Going to check the PCV hose today. I don't think the converters are clogged.... I just bought them last year. We will see. Has to be SOMETHING! Thanks for the suggestions!

 

also check the egr valve, very common problem for the 12v engine. it may just need to be cleaned. seafoam would probably be the easiest fix though so try that first