jpda8

I have an 1998 audi a8 quattro that is misfiring on 7 and 8 cylinders when accelerating between 70 and 75 mph. I also noticed that it misfires at 60mph in 4th gear, but doesn't throw a code. This all seems to be when I accelerate at around 2000 RPMs. I believe it is a faulty MAF. My mechanic already replaced the coil packs and spark plugs, but this didn't fix the problem. I don't notice any performance problems, but it consistently throws a code when I am cruising between 70 and 75 mph.

Any Ideas?

Mr. Z

No codes or blatant misfire (I think), but I get "funny business" @ 40 to 60 mph & 2K RPM

Acceler8

I thought my 2000 was misfiring in that range and it turned out to be vacuum hoses.

jpda8

Yes, I gradually accellerate between 70 and 75 and the MIL light comes on and the code signifies a misfire on mutiple cylinders. Normally, it is 7 and 8, but somtimes other cylinders as well.

jpda8

I also was having the same problem without it causing the MIL light to go on. At first, I thought it was a tire balanacing issue because I would get this vibration and it felt like a problem with the tires. I replaced all 4 tires, but the problem didn't go away. Only recently did the MIL light start coming on and I took it to my mechanic, but he couldn't figure out the problem.

jpda8

I do notice that when I first tart the car and accelerate, that there is a lot of air noise coming from the engine department as if there was a loose hose or hole somewhere

Mikalai

Fuel pump is ready to die. Its look like first simptoms of that.

Mr. Z

Vacuum hoses? It could just be my imagination, but I hear a faint, "metallic" hiss on acceleration.

Always Overcharged

Then you have a starting point
Suggest scan each set on an open rd with a passenger who puts in a marker whenever you think there is a misfire.
If it is your ignition it will fluctuate around or just before the marker and if it is fuel related it willshow in the mixture adaption.
It is a good way to isolate the cause of intermittent faults