Drivability issue possibly tied to A/C? 2003 BMW 325i (E46)


Bouncing idle, stalling, RPMs fall too fast or hang... only when A/C is ON. 2003 BMW 325i, 5spd (E46)


For a few years now I've had a drivability issue that seems to manifest itself in hot weather and I've recently discovered that I can reproduce the symptoms (or make them go away) on demand by simply pressing the A/C button to turn the compressor ON and OFF. Symptoms surface when the A/C is ON and are as follows:

  • After the engine warms up, when I pull up to a stop light and throw the car in neutral (it's a manual), the RPMs will bounce
    • sometimes they bounce slightly and then settle down somewhere between high 500s and around 700
    • at times they bounce erratically (as much as 600 or 700 RPM, up and down)
    • after some short amount of time (less than a minute) of erratic bouncing, the engine will die
  • While driving it is difficult to upshift and downshift smoothly through the gears because engine response is inconsistent, meaning:
    • RPMs either drop too fast (much faster as compared to when the AC is off)
    • or the RPMs will hang too long and I end up over revving

This makes for an annoying driving experience not only for the passengers, but for me as well. I've been driving manual cars for many years. My other car is also a manual and I do not have this problem with it. Both cars are similar, BMW E46 platform. The problem car is a 2003 BMW 325i, sedan, 5spd, M54 engine, 117k miles. I have to admit, before I discovered that I can make the problem go way by turning the AC off, I threw parts at it for a while to include:

  • camshaft sensors,
  • ignition coils,
  • and DISA valve.
  • I did of course change the air filter (as I do regularly),
  • but I also took the throttle body out and cleaned it thoroughly with CRC Throttle Body cleaner.
  • I also cleaned the MAF with CRC MAF cleaner.
  • The fuel filter was replaced within the last 35k miles or so
  • The spark plugs have also been replaced within the last 35k miles or so
  • The belts (including the AC belt) have been replaced within the same time frame of 30k-40k miles.

I have to mention that a few years ago I did use a diy kit from a local parts store to add refrigerant to the system. (I know now that this is a big "no-no".) I wonder if there is too much refrigerant in the system, perhaps? I can tell you that the AC blows super cold!

Any suggestions as to how I may go about diagnosing this issue would be greatly appreciated, Scotty. (I am tired of throwing parts at it.)

Thank you in advance!

And thank you for the awesome benefit you provide to all of us car enthusiasts. My boys (who are 4 years young and 2 years young) love to watch your videos with me. Your videos are entertaining and educational and if they're going to have "screen time", I'd rather they watch you than the alternative.


Comments (3)
No. 1-3

Additionally, I want to mention that while driving, with and without the A/C ON, I show a voltage between 13.9 and 14.2. I read it using my Belkin radar detector which happens to have the capability to display voltage.


Thanks for responding, Scotty, and for the advice. I had the battery tested a few months back at Firestone and was told it wasn’t pulling the cranking amps that it’s suppsed to. It’s 5 years old. Having said that, I haven’t had any starting issues whatsoever.

Can I have the alternator load tested while it’s in the car without any negative effect on the electronics in the car? Is that a safe thing to do or do I need to remove it and bench test it?

(Did not see your response to this until just now as it ended up in my spam.)

Thank you for what you do for the community!




turning on the AC strains the electrical system. FIRST, have the battery and alternator load tested, weak ones will do just that. Pray it's that and not computer module failures which cost a ton on those BMWs