Bigrick31

I have a 97 a4 2.8 quattro 160,000miles. I was having a problem with the car idling really rough to the point of almost dying when I would stop. The car would also accelerate really slow. I recently replaced the coils, spark plugs and spark plug wires to fix the problem and while it did help the car still idles really rough and if you press the gas pedal all the way to the floor the car will slowly rev up where as before the tachometer used to climb very rapidly when the gas pedal would be pressed to the floor. The only error code I get is p0300 and I hear the car backfiring through the exhaust when I give it a lot of gas.

Ive read that common causes could be

oxygen sensors
MAF
Catalytic converter clog

im not really sure where to go from here as the p0300 code is very vague and any 3 of the above parts that may need to be replaced are very expensive. Does anyone have any idea how I can narrow down the possibilities?

AudiMick

I wouldn't do any of that.

Clean the ICV .

Info here, very common problem on the 12 valve particularly at this time of year, once the AC is locked out due to lower ambient outside temps the idle RPM should drop.The ICV tend to have trouble adjusting and the motor will stall.

Replace the vacuum lines, they will be leaking by now on a 14 year old car.

Check the gasket around the throttle body to plenum.

Borrow/ buy a Vag.com and check for the Audi codes, the generic readers aren't always correct.

http://audi.kris-hansen.com/icv.htm

The black plastic valves have a B shaped cap on the bottom of them , if you can "carefully" pry that off you can clean around the moving piston of the valve much better. Just re-glue it afterwards.

Bigrick31

Ill give that a shot in the morning Thanks!

turbo510

Did this lack of power happen gradually or suddenly? If fairly sudden, I wouldn't blame the cats. Secondly, the MAF can be disconnected to see if the engine runs better without it. And O2 sensors wouldn't cause an engine to rev slowly. Maybe the ICV does need cleaning (however I've never had to service mine with 216K miles) but that wouldn't fix the low power, something major is causing that. Bad idle, weak power could even be from low fuel pressure.

Bigrick31

When I got my ICV off it didnt look very dirty at all. I cleaned it up anyways put it back on but nothing changed.

The lack of power happened pretty much over night. One day the car was running like normal and then next it was barely drivable. It was shortly after I was rear ended in the car now that I think about it. It was a hit and run so the car was never sent to a shop for the damage to be assessed but the only signs of the accident is some chipped paint on the bumper of the car but maybe something happened to the fuel system as a result of the accident? It was maybe a month after the accident that we started having problems.

Before the accident we had the timing belt and water pump replaced along with the front upper control arms.

turbo510

I'd really expect the problem is fuel-related, especially when the only code you get is the one listed. You really should get a VAG-COM scan, and check the throttle position, MAF, coolant temp to see whether these are normal. Another thing you could try is to remove the fuel return hose at the tank top, extend the hose to dump into a gas container, then run the car and see if the fuel pressure from the pump is high enough to operate the pressure regulator valve (evidence would be fuel flow into said container). This test assumes the FPR is ok.