Auto Electronics: 2001 nissan altima SE 2.4 L., throttle position sensor, mass air flow

Question
my car is surging while sitting at red lights.its still surging after complete tune-up.it doesn't surge as bad while air conditioner is on.ran test.the test showed rapid fire,knock sensor,and running lean.could the problem be caused from throttle position sensor?

Answer
Iorie, while I would not rule out the Throttle Position (TP) sensor, it would not be my top candidate for the fix. Obviously you must have scanned the system and gotten both a lean and knock sensor code. I’m not sure what a rapid fire code would be, unless you are talking about a miss fire code. Surging at idle does suggest a lean condition and should be looked into further by checking the fuel trims at idle. Positive fuel trims would indicate a lean condition, as the processor is trying to add more fuel attempting to correct for the lean mixture. If the lean condition is confirmed, start looking for an intake manifold leak downstream of the Mass Air Flow (MAF) sensor. The intake gasket on this vehicle is known to have problems and should be checked first. The MAF sensor cannot be ruled out and don’t forget about that knock sensor code. Both would need to be diagnosed following the manufacturers procedures. Good luck. Don.