idle surge pulse when A/C turned on, and when coming to stop - MustangForums.com



4.6L V8 Technical Discussions Any questions about engine, transmission, or gearing can be asked here!

Reply
 
 
 
Thread Tools Search this Thread
Old 08-09-2018, 03:00 PM   #1  
Dan Diego
Thread Starter
 
Join Date: Aug 2018
Location: CA
Posts: 2
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.
Dan Diego is offline   Reply With Quote
Old 08-10-2018, 02:16 PM   #2  
Derf00
6th Gear Member
 
Join Date: Feb 2005
Location: AZ
Posts: 11,274
Default

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.
Derf00 is offline   Reply With Quote
Old 08-12-2018, 07:23 PM   #3  
Dan Diego
Thread Starter
 
Join Date: Aug 2018
Location: CA
Posts: 2
Default

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
Dan Diego is offline   Reply With Quote
Old 08-13-2018, 01:28 PM   #4  
Derf00
6th Gear Member
 
Join Date: Feb 2005
Location: AZ
Posts: 11,274
Default

Nice, glad that got you fixed!
Derf00 is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
low idle at start up and coming to a stop mikefurno GT S197 General Discussion 2 01-02-2014 08:06 PM
low idle and surge at start up and park StevoX1 5.0L (1979-1995) Mustang 3 06-23-2013 01:39 PM
won't idle when coming to a stop! jas05stang GT S197 General Discussion 6 01-25-2013 06:56 PM
hanging idle to idle surge? anrtman 5.0L (1979-1995) Mustang 5 12-22-2008 09:58 PM
In regards to idle surge and idle hanging 88_GT_5.0 5.0L (1979-1995) Mustang 1 09-30-2006 10:11 AM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Forum Jump

Advertising
Featured Sponsors
Vendor Directory

All times are GMT -5. The time now is 10:53 AM.


© 2018 MH Sub I, LLC dba Internet Brands
We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.