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idle surge pulse when A/C turned on, and when coming to stop

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idle surge pulse when A/C turned on, and when coming to stop

Old 08-09-2018, 04:00 PM
  #1  
Dan Diego
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Join Date: Aug 2018
Location: CA
Posts: 3
Default idle surge pulse when A/C turned on, and when coming to stop

My 2005 Mustang GT has recently began to have idle surge issues. If I turn on the A/C, the idle will surge in a series of pulses, sometimes once but more often 3 or 4 times before returning to a normal idle. This also happens when driving with he A/C on, then coming to a complete stop. The idle will again surge in pulses for 1 to 4 times. The guy or gal I pull up next to often must be wondering if I am revving the motor, begging for a race from the stoplight. Some want to go. Some are amused. Most of the cops, however, are not. My A/C is properly charged and blows cold air. I have a modified exhaust along with K&N cold air intake since I bought 5 years ago. The problem is only recent though. I do not have any MIL codes present. I would be grateful for any thoughts or advice.
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Old 08-10-2018, 03:16 PM
  #2  
Derf00
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Join Date: Feb 2005
Location: AZ
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Inspect and clean your throttle-body plate and MAF sensor.

The AC adds and removes a load on your engine that requires the computer to adjust the engine's idle parameters to compensate when the AC kicks on/off.

If the TB or MAF sensor are dirty/not registering correctly, that sends a bad signal to the PCM which then takes a few tries to find the right parameters to idle again.

You can do a quick test. With the car idling and the AC OFF, just stab the throttle (get it to like 3K) and let it drop back down to Idle, it should find the idle with ZERO surging or hunting. If it bounces/hunts/surges, even once, then its most definitely worth cleaning both the TB and the MAF.

The other possibility is a tiny intake leak that the car can compensate for (thus no codes) but is enough to affect the idle. Noticed any loss of power when WOT?
Let us know what you find.
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Old 08-12-2018, 08:23 PM
  #3  
Dan Diego
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Join Date: Aug 2018
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Thank you Derf! Problem solved. I cleaned the throttle body plate with carb cleaner and tooth brush and towels and then cleaned the MAF sensor with q-tips and alcohol (non-tequila). Viola! No more surging when the AC is on. Furthermore, particularly when the motor was cold, take offs in first would result in some "bucking". That has been fixed as well. I have put up with that for years. So very pleased now. Gonna celebrate with a cruze! Cheers!

Dan
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Old 08-13-2018, 02:28 PM
  #4  
Derf00
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Nice, glad that got you fixed!
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