sodowarts

My 2004 A6 3.0 is doing some serious RPM spiking when its in the idle mode and when taking my foot of the brake it sometimes does quick lurch and then settles down. Any insight to the problem and the likely fix would be appreciated. thanks.

Redneck Truck

have you checked for codes? more information on the car would be very helpful.

could vacuum be leaking from the brake booster? get a vacuum gauge on it, pull vacuum, and see.

sodowarts

I think the code is referring to the air flow meter. Does that sound right? What do you think that would cost to replace?

Redneck Truck

If it's the mass air flow meter, I'm even more convinced now that you've got a vacuum leak. Vacuum leaks means air getting in after the throttle body, which is after the MAF, which renders the MAF's signal inaccurate. Whether or not that's what caused the code, I'd check every place that holds vacuum: the intake manifold, the throttle body, the vacuum lines, the brake booster, and any vacuum operated accessories, suction pumps, the EVAC system, until you find a cracked, crumbly vacuum line, a leaking seal, or some other way that air is getting in where it shouldn't.

sodowarts

Thanks Redneck! Do you know what the code number(s) would be for this problem?

Redneck Truck

For vacuum leaks? There are no vacuum leak sensors, so it would manifest itself in other ways, like bumpy, spiky idle, MAF codes, etc. Open up your hood, use your key to remove the engine covers, and take a look around. You'll be surprised at what you find.

sodowarts

For what its worth I got the codes:

18339
16487
16497
17535
17537
16891
17550
17658

My guy said something about being too lean vs rich to be a vacuum leak (or maybe he said to rich vs lean).. not sure.

Let me know if this info helps at all with your diagnosis......

Redneck Truck

Lean condition would also be a vacuum leak - too much air for the fuel metered by the MAF. When I hear rich I think RPM drops, poor idle, poor fuel economy, smelly exhaust, smoke in exhaust.

That's a nice list of codes. Care to google them? :-)