Rough idle when air is on

[ttopstang]

The car idles fine util you turn the air on then it jumps up and down and will even go down so low to shut off some times. Car is bone stock 92lx 5 spd.

I adjusted the TPS to .98, and timing is at about 13*, but I havn't cleaned the IAC yet. I have never owned a mustang with air so I was wondering if theres another step I should take.

 

[boxcarracer89]

Ive got the exact same problem, but mine is extremly modded!

 

[HISSIN50]

Any codes?

If the idle is ok at all other times (suggesting a vac leak is not the issue), the IAC is probably acting up. Sometimes they figure themselves out if your car just recently came out of hybernation, but since your car is stalling, cleaning or replacing it might be needed.

 

[ttopstang]

I don't think its a vacuum line, but I will check, and I will be cleaning the IAC. Idle is good all other times, only when A/C is on.

And the voltage jumps up and down ALOT as you rev it. I think its the alternator getting pissed at that electric fan.

 

[jrichker]

See the "Surging Idle Checklist for help with all your idle/stall problems. Everything you need to find and fix idle problems is in there.

The first two posts contain all the updates to the fixes. At last count there were 24 possible causes and fixes for surging idle/stall problems. I continue to update it as more people post fixes or ask questions.

 

[Haus]

I don't think its a vacuum line, but I will check, and I will be cleaning the IAC. Idle is good all other times, only when A/C is on.

And the voltage jumps up and down ALOT as you rev it. I think its the alternator getting pissed at that electric fan.

Did you upgrade from the stock Amp Alternator?

but anyway im interested in finding out your results. My car does the same, but i think my IAC is starting to go.

 

[ttopstang]

Stock alternator for now.

jrichker, I found your thread right after I posted and its very informative. I will try to keep yall updated but I probably won't be able to get to it until this weekend.