Engine Lopes When I Start Engine With A/c On

[Bruce999]

Hi folks

99 Boxster 2.5, 5 speed, 39K miles.

Here in Mesa, AZ, it's hot and when I start the engine in the morning or after sitting a while, the engine lopes and car shudders for a little (with A/C on only).

Was told by a friend who has a BMW 7 series that this is normal.

Anybody ever have this happen?

Thanks

[number9ine]

Hi folks

99 Boxster 2.5, 5 speed, 39K miles.

Here in Mesa, AZ, it's hot and when I start the engine in the morning or after sitting a while, the engine lopes and car shudders for a little (with A/C on only).

Was told by a friend who has a BMW 7 series that this is normal.

Anybody ever have this happen?

Thanks

I'd say it depends on how much the car shudders. When you activate your AC the clutch on your compressor engages, which will change the engine's operating state slightly due to the increased load. On most cars you can feel this engagement briefly, but not for long. If it's very hot out I notice the additional noise and load from the compressor in all my cars.

Your car is about 20k short of a polyrib belt maintenance according to the book, but your car is over 10 years old so it may be worthwhile to do now. If the belt is worn, it could contribute to what you're experiencing. Since the belt is cheap and the process can be done DIY, I suggest you start there. While you're in there you can check the accessory drive items for play and examine the car in a running state with the seatback engine cover off. Should the symptoms persist with a belt change, it could be your compressor--years of hard duty in the AZ sun could be causing it to fail. Get it checked out before it packs up.

Mark

[wvicary]

I would clean the throttle body and idle speed motor.

[Bruce999]

Thanks for your replies.

I had thought about replacing the accessory belt since the cars is 11 years old.

I just replaced the MAS and fuel pressure regulator last weekend...

:D

[Bruce999]

OK, I replaced the belt. Checked all the pulleys for play. None had any play whatsoever, except just a very slight play in the alternator pulley, so I am relieved to see the are no obvious issues with the compressor. Go the new belt from NAPA and it worked out perfect. The issue is still there, but maybe (and I say maybe) just slightly less shudder. I start the engine with the A/C on, then the engine surges (as it does normaly), then drops to 500 RPM or so momentarily as soon as the DME detects that the A/C is ON, then picks up again. At 500 is when I get the momentary shudder. Worked on the truck this weekend so I will set a weekend in the near future to clean the throttle body and iddle control motor.

B)