on my Mustang, when the A/C is on, the idle speed does not change. So, when I accelerate, then come to a stop at a light, the car runs rough, or almost stalls. So I am guessing there is some relay or switch that is not kicking up the idle speed. Any ideas?

 

iac

 

as stated above, sometimes you can clean them and get rid of the carbon buildup or just buy new. When i did mine i ended up buying new and worked perfect.

 

i already tried cleaning it out--it may be time for a new one. Thanks, guys!!

 

I'm thinking a vacum leak. HVAC controls are vacum operated. Check for leaks mainly the one that supplies vacum to inside the car. Check the vacum T real good

 

thanks!!

 

Did you get it sorted out? Verdict?

 

new IAC helped, but did not fix the problem. I checked the vacuum lines, I didn't seem to find anything as far as vacuum lines go, but I did fine the PCV valve blown of at the back of the intake. THe idly still does not speed up when I turn the A/C on, so I doubt it is fixed.

 

It could still be your IAC ... so just to be safe ... with the car off and the key in running post. check your IAC with a multi-meter it should read 10.5-12.5.

If the voltage is fine then it could be your idle speed period. As long as your car is running fine pull the service plug out of the throttle orfice and turn the screw clockwise. Factory idle is aabout 500-600 RPMS
Pay attention for any fluctuations in your idle. If you do have them then there is an air leak someplace.

Which would make sense because i also beleive it could be a vacuum problem and if you have low vacuum the PCV will never restric flow and it allows to much blow by gasses to come through which builds up high pressre and blows out the PCV.

 

Thanks for the info, Tony. I just need to spend some time to look around. Since this is not my daily driver, it gets pretty low priority. I have removed/added parts using vacuum lines, and the car is at the age where a line under the hood could be split and hard to find. I could not event tell you at this point when the problem started.

When I find the problem, I let you guys know--I appreciate all the feedback!!!