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Discussion Starter #1
I have a 1997 Z3 1.9 manual transmission.
When the AC is on, the idle speed will fluctuate between 500 to 1000rpm for a few seconds when the shifter is in neutral. It is almost stalling. This does not happen when the AC is off.
I searched the archives but found to answer. Has anyone else experienced this situation?

Thanks.
 

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I have a 1997 Z3 1.9 manual transmission.
When the AC is on, the idle speed will fluctuate between 500 to 1000rpm for a few seconds when the shifter is in neutral. It is almost stalling. This does not happen when the AC is off.
I searched the archives but found to answer. Has anyone else experienced this situation?

Thanks.
Try to slowly release the clutch pedal in first gear on a flat surface with AC off and idling engine, without touching the gas pedal. If the engine moves the car without major struggling, then your AC compressor is having too much resistance when on and gives a hard time on the engine.
 

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Discussion Starter #3
Thank you for such a quick response. I tried it as you said with the AC OFF and also with the AC ON. The car vibrated for a short period in then went forward with no problem both with and without the AC.
 

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BMW CCA 1405
1997 BMW Z3 1.9
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I have a 1997 Z3 1.9 manual transmission. When the AC is on, the idle speed will fluctuate between 500 to 1000rpm for a few seconds when the shifter is in neutral. It is almost stalling. This does not happen when the AC is off....
How long have you had the car, and when did you notice this?
I have the same car, though I rarely use the AC. It sounds like the compressor is cycling on and off. When on, it is a load that drags the idle down, but the engine's controls bring the RPMs back up in a few seconds. That is normal.
If you have had the car awhile, and this is some new and different change that is concerning you for the first time, then it would not be normal.
 

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Thank you for such a quick response. I tried it as you said with the AC OFF and also with the AC ON. The car vibrated for a short period in then went forward with no problem both with and without the AC.
sounds like the engine side is ok. Must be the AC compressor then. I don't know much about AC but I heard that when replacing refrigerant they can add some oil to lubricate the compressor, that might save you from replacing the compressor. Search for that, I can't remember any more.
 

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BMW CCA 1405
1997 BMW Z3 1.9
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I just used my AC for five minutes, not long enough for it to cycle, but I turned it on and off a few times. And the compressor drops the 750 RPM idle just a little for a second, hardly enough to notice.
So I think your 1000 idle is too high, and the drop to 500 is too much, and almost stalling is not right.
Again, a few answers about your car would help. How many miles, how long have you had it, is this a change and when did it begin, does the AC work, has anybody done anything to it lately?
 

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Discussion Starter #7
Well the car has 106K. Have it for 3 months now. The AC was causing the car to idle rough when I first got the car. Then the AC stopped working and need a recharge. I noticed it after recharging it this afternoon.
Interestingly, this evening I tried the AC again. This time the idle dropped to around 500 rpm briefly and rpm settled at 750 rpm when pressed the clutch. The fluctuations are not as marked.:dunno:
 

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BMW CCA 1405
1997 BMW Z3 1.9
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... the car has 106K. Have it for 3 months... The AC was causing the car to idle rough when I first got the car. Then the AC stopped working and need a recharge. I noticed it after recharging it...
I would go to an AC shop to get it sorted out, or repaired if needed. The compressor could have stopped because it was damaged by lack of refrigerant, and then you could have overcharged it unless you have gauges and know what you are doing.
 
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