alfa_romeo55

Hello BMW people, recently I purchased a 05 545i with a 6 speed gearbox. I have noticed while driving at 70 mph you feel the engine surge a bit. No increase in speed but definitely feel the engine surge and pull back, surge and pull back. On some occasions while idling the tachometer needle will drop from 800 rpm to 500 rpm and back up again all by itself. Also if the A/C is near high blast you hear it speed up and slow down...... Any suggestions to the problems above will be greatly appreciated............. Thanks

rocksteady530

My recommendation would be to read your computers for any error codes. If you don't have the tool to do so, most auto parts store can do it for you for free....I know Autozone does. Those symptoms could be any of several things...MAF senosr, Idle control valve, etc. First step see if the car is throwing any error codes.

kushane

Switch the transmission over to d/s and see if the surge happens only in 5th. Your symptoms describe a pretty well known issue with some of the zf transmissions and there are several threads on that issue.

alfa_romeo55

There are no idiots lights on or "check engine" light so how would I know if there are any codes???? Also its a 6 speed manual gearbox and not automatic, so putting it in d/s doesnt apply.

528canyonrot

I dont believe the n62 engine has a idle control valve like the m62.

528canyonrot

you dont necessarily have to have a light on the dash. Sometimes you can have a pending code. What are Pending Codes?
OBD II Pending Codes are also referred to as “continuous monitor” and “maturing codes”. An intermittent fault will cause the computer to store a pending code in memory. If the fault does not recur within 40 warm-up cycles, the code will be cleared from memory. If the fault recurs a specific number of times, the code will then mature into a diagnostic trouble code (DTC) and the MIL or “check engine” light will turn on

alfa_romeo55

ok... I'll check the codes and get back yo you......