382WS6

Just wondering... but how can I tell if my Air Pump is going bad? My car idles rough (sounds like it's deiseling... jumps up and down, not a lot, but enough to feel it, hear it, and see it on the tach). Somebody mentioned to me that the Air Pump might be going bad. That and my gas mileage is way down. I'm at a loss since I just had it tuned and nothing was mentioned to me about thrown codes or anything. Thanks for any help.