I've been having this problem lately...

I have a NA S4, with less than 68k miles on the engine.

Daily driven, with no mods other than a cone air filter and NGK plug wires.

Other than that, it has HID lamps.

My problem is the following -- on deceleration I get a fair amount of bucking, and if I shift to neutral and step on the brakes, revs go reaaallly low... sometimes it goes back up to normal 750rpm idle speed slowly by itself, others the car decides to blip on the accel to make revs go higher, and other times the car simply stalls.

What could cause this?

I noticed that the air pump's little air filter (since I have a cone air filter, I had to get a separate filter for the air pump) is pretty dirty... could that be it?


Any info/feedback will be greatly appreciated

 

Help?

 

Sometimes I feel like a broken record. But that set aside:
Check your TPS, BAC for leaks, and AFM