[shanes]

I’m having this issue with my 2011 328i. With the AC off the engine idles perfectly smooth.
When the AC is on the idle oscillates about every 3-4 seconds about 100 rpms up then back down... usually doesn’t do this when the car is first started, and there are times that if MAX AC is switched on it won’t do it.. but only sometimes this change happens.
AC is ice cold.
Ran Carly, no codes.
Compressor isn’t noisy.
After some reading.. I found that this is a variable displacement compressor / no clutch, and something is intermittently making the compressor appear to be turning on and off every few seconds at idle intermittently?
Anyone have any answers.. appreciated?

[marvinstockman]

Your idle air control valve may be dirty and slow. Try cleaning it.

Remember, the AC puts a load on the engine, and the valve is supposed to keep rpm's steady.

[lowrydr310]

Originally Posted by marvinstockman

Your idle air control valve may be dirty and slow. Try cleaning it.

Where exactly is the idle air control valve on these cars?


I thought the N52 had 12 idle air control valves managed by the valvetronic motor. (being a bit sarcastic here - it was my understanding that the idle is controlled directly by the intake valves, with lift being managed by the valvetronic motor and no standalone idle air control valve)

Regarding the original question of fluctuating idle, I'm fairly certain that's normal behavior. The AC puts quite a load on an idling engine, and the RPMs may fluctuate as the car adjusts to the demand.

[e90yyc]

I had these same symptoms a few years back and changing the spark plugs solved it for me. They were due to be changed so it made sense. Not sure when yours were last done, so perhaps that isn’t the issue for you.

[marvinstockman]

Low Rider, you're right, no idle air control valve. Too bad, as it would have been an easy fix for the OP.

[marvinstockman]

Also, for being wrong, will I get demoted back to a private?

[lowrydr310]

Originally Posted by marvinstockman

Also, for being wrong, will I get demoted back to a private?

Not a chance. Even the best leaders still make mistakes sometimes.

[shanes]

Thanks guys.. this is really unusual behavior. I noticed it a couple months ago. It’s as if the idle bobs up and down every few seconds only when AC is on, and sometimes when I change temps, or turn on Max AC it will normalize for a noticeable amount of time.
I changed out the plugs about 40k ago with NGK iridiums.. just cleaned the MAF the other day.
Strange. I’m used to a solid 750 rpms with ac on and maybe 650 off.

Now I know these cars have a Clutch less variable displacement compressor..
I thought I read somewhere that the actuator that adjusts the displacement.. something with the swash plate could be the problem? Grant it. AC is great.

[toufher]

Hi, did you find a solution to this problem? My wife's car has the same problem...

[shanes]

I didn’t find the problem.. there’s a chance that it could be refrigerant level being low.
I just sold the car a week ago.

[BrazilianBimmer]

I have this same issue on an e90 325i. Rpm fluctuates when AC is on and sometimes after ac is turned off rpm fluctuates at traffic light idling

[toufher]

I have scheduled ac service for next week. Let's see if that is going to fix the problem.

[toufher]

Originally Posted by toufher

I have scheduled ac service for next week. Let's see if that is going to fix the problem.

Service topped refrigerant. This helped little bit as rpm fluctuation isn't as bad as it was before. But still it didn't solve the case. Will the rpm fluctuation be bad on engine? Could it break it?

[marvinstockman]

The extra refigerant probably allowed the system to run under a constant load without shutting down, and cycling, on low pressure.

Now, if you live north of the artic circle, you shouldn't need AC anyway.

Unless the rpm surges to 7000, you're really not going to hurt anything.

Have you tried moderating the surging, that is until you find the problem, with the gas pedal?

Remember, the computer is trying to maintain a steady rpm under a changing load, but something else is wrong, causing the surging.

[bobbby]

Not sure if applicable to your situation but I had this rpm issue with my n55 and the issue was resolved when my mechanic noticed the aftermarket chargepipe that was installed had a screw pop off which was causing irregular airflow. After putting in a new screw to plug the hole, issue was fixed.