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5.0L (1979-1995) Mustang Technical discussions on 5.0 Liter Mustangs within. This does not include the 5.0 from the 2011 Mustang GT. That information is in the 2005-1011 section.

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Old 05-02-2014, 08:53 PM   #1
MacSerio
 
Join Date: Apr 2013
Vehicle: 1990 Ford Mustang GT Convertable
Location: California
Posts: 24
Default 91 GT Strange idle issue after throttle pressed???

FIRST OF ALL: I was having issues with egr system, the line that connects to the egr valve was having constant vacuum. I cleaned it out and it started working properly. The next day, it started doing the same thing. The vacuum came back on the line that connects to egr, it stopped after i cleaned it the first time but now its sucking air again....What causes this?
SECONDLY: And my idle is pretty steady at about 7rpm if i start the car with that egr line unplugged, but as soon as i hit the throttle once, the idle gets all screwed up and starts jumping around 6-7 rpm. If i turn the car off and immediately start it back up, the idle will be fine again; but as soon as i start driving or tap the throttle...bam the idle becomes eratic again. What should i look for or check. I cleaned out most sensors and checked all vacuum lines,, what else could it be?
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Old 05-02-2014, 09:06 PM   #2
dawson1112
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Join Date: Jul 2012
Vehicle: 1990 lx hatch 5.0
Location: ohio
Posts: 2,643
Default

That vacuum is supplied by the egr vacuum solenoid. You may need a new one.

A for the surging idle from 600-700 rpm you could have a vacuum leak and that solenoid may be the culprit.
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Old 05-02-2014, 09:39 PM   #3
mongolchuck
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Join Date: Feb 2007
Vehicle: 1991 LX Convertible
Location: IA
Posts: 150
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I just want to thank you for spelling vacuum correctly.
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Old 05-02-2014, 09:58 PM   #4
MacSerio
 
Join Date: Apr 2013
Vehicle: 1990 Ford Mustang GT Convertable
Location: California
Posts: 24
Default

well i just cleaned that solenoid a second time, and it seems to be working properly once again. it is not sucking air at idle any longer. Yet my idle is still quite erratic....is there a sure tall tale way to diagnose a bad balancer? i see a bit of wobble and minor wear on the rubber ring...
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Old 05-02-2014, 10:03 PM   #5
MacSerio
 
Join Date: Apr 2013
Vehicle: 1990 Ford Mustang GT Convertable
Location: California
Posts: 24
Default

i doubt the solenoid is causing the idle issue, as the issue remains with the solenoid unplugged as well....after resetting tps and idle, it wont idle smooth at startup like it did before, but it does seem to be running better and idle a bit better after throttle...and ive fixed all vacuum lines, i dont see that being the problem now either.

Last edited by MacSerio; 05-02-2014 at 10:06 PM.
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Old 05-02-2014, 10:03 PM
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