Rough Idle
Senior Member
Joined: May 2003
Posts: 332
Likes: 0
From: LI, NY
02 W163, 84 W123, 03 E39, 98 E39
Rough Idle with A/C
Happend to me with a C-220. Dealer said it is common to be rough.
Is it just rough, or does it seem like the engine is pulsating every couple of seconds, changing revs by 2-300 rpm? If it is pulsating, then your A/C may be overpresurized with coolant and the A/C unit may be turning on/off every couple seconds and causing the engine reves to fluctuate. This tends to happen in hot (over 90F) temps if it is over presureized.
Is it just rough, or does it seem like the engine is pulsating every couple of seconds, changing revs by 2-300 rpm? If it is pulsating, then your A/C may be overpresurized with coolant and the A/C unit may be turning on/off every couple seconds and causing the engine reves to fluctuate. This tends to happen in hot (over 90F) temps if it is over presureized.
Last edited by sph17; Jul 27, 2003 at 10:26 PM.
Thread Starter
MBWorld Fanatic!
Joined: Apr 2003
Posts: 4,781
Likes: 3
From: Boston
'05 A4 1.8TQM6
Yea, seems to pulsate, like u said every few seconds. The RPM needle will jump kind of when it starts to pulsate...maybe just normal when it's hot outside and with A/C running for a 4 banger.
Senior Member
Joined: May 2003
Posts: 332
Likes: 0
From: LI, NY
02 W163, 84 W123, 03 E39, 98 E39
Pulsation with A/C
When you start up the car and it pulsates, go look under the hood at your compressor. Check to see if the compressor clutch is clicking on/off every few seconds. If it is, then your A/C may be over presurized.
This happened to me whenever it was very hot out, and my car was driven a while, parked for a few min. and then re-started. This happened to me for 4 months, until almost by luck I noticed this w/ a MB Tech. When he saw that the A/C clutch was cycling on/off he knew that this was caused by over-pressurization.
This happened to me whenever it was very hot out, and my car was driven a while, parked for a few min. and then re-started. This happened to me for 4 months, until almost by luck I noticed this w/ a MB Tech. When he saw that the A/C clutch was cycling on/off he knew that this was caused by over-pressurization.
Thread Starter
MBWorld Fanatic!
Joined: Apr 2003
Posts: 4,781
Likes: 3
From: Boston
'05 A4 1.8TQM6
Re: Pulsation with A/C
Originally posted by sph17
When you start up the car and it pulsates, go look under the hood at your compressor. Check to see if the compressor clutch is clicking on/off every few seconds. If it is, then your A/C may be over presurized.
This happened to me whenever it was very hot out, and my car was driven a while, parked for a few min. and then re-started. This happened to me for 4 months, until almost by luck I noticed this w/ a MB Tech. When he saw that the clutch was cycling on/off he knew that this was caused by over-pressurization.
When you start up the car and it pulsates, go look under the hood at your compressor. Check to see if the compressor clutch is clicking on/off every few seconds. If it is, then your A/C may be over presurized.
This happened to me whenever it was very hot out, and my car was driven a while, parked for a few min. and then re-started. This happened to me for 4 months, until almost by luck I noticed this w/ a MB Tech. When he saw that the clutch was cycling on/off he knew that this was caused by over-pressurization.
Senior Member
Joined: May 2003
Posts: 332
Likes: 0
From: LI, NY
02 W163, 84 W123, 03 E39, 98 E39
Re: Re: Pulsation with A/C
Originally posted by GDawgC220
This may be a silly question, but what is the compressor clutch? And what is the remedy for overpressurized A/C?
This may be a silly question, but what is the compressor clutch? And what is the remedy for overpressurized A/C?
The A/C compressor has an electrically operated clutch. When the clutch is "off" the front of the clutch does not go around in circles. When the A/C clutch is electrically activated, you can see the front of the clutch start spinning. You can watch this by opening your hood, look for the A/C compressor on the front drivers side of the engine, and have a second person turn the A/C On, then Off. Once you see what I am describing, then next time your car pulsates, go open the hood, and see if your A/C clutch is turning On/Off every couple of seconds.
The fix for this is to have a qualified A/C service center (dealer, service station, or repair shop) check the pressure of the coolent in your A/C system. In the olden days this would be called checking the Freon level, but newer cars don't use Freon (or other CFC's) because they are environmentaly unfriendly.
Let me know what you find.
Last edited by sph17; Jul 27, 2003 at 10:57 PM.
