89 5.0 Ho 5 Spd Stalls At Idle With A/c On

Hi! New today. Left here: https://mustangforums.com/ today, seeking a better forum. My idle problem similar, it's a '94, still EEC-IV, pretty same as '89. Runs perfect as long as it's not shut down. Then, if restarted in 10 min. or so, starts normally, up to ~ 1000 rpm, drops to ~ 500, jumps up again, down again, maybe third time dies, or evens out to normal.

Have a brand-new 5.0HO sitting in the corner, so yanked off the TB, with TPS and IAC, stuck it on the car. Same problem. Thinking ECT sensor? Any ideas appreciated! Also, at 161K, maybe original HO2S, when it goes closed-loop, maybe......but why wait until shut-down. For kickers, it doesn't happen every time, maybe 75%. If I start hot, hold rpm at ~ 1200 for 5 secs., everything normal. imp

imp said:

Hi! New today. Left here: https://mustangforums.com/ today, seeking a better forum. My idle problem similar, it's a '94, still EEC-IV, pretty same as '89. Runs perfect as long as it's not shut down. Then, if restarted in 10 min. or so, starts normally, up to ~ 1000 rpm, drops to ~ 500, jumps up again, down again, maybe third time dies, or evens out to normal.

Have a brand-new 5.0HO sitting in the corner, so yanked off the TB, with TPS and IAC, stuck it on the car. Same problem. Thinking ECT sensor? Any ideas appreciated! Also, at 161K, maybe original HO2S, when it goes closed-loop, maybe......but why wait until shut-down. For kickers, it doesn't happen every time, maybe 75%. If I start hot, hold rpm at ~ 1200 for 5 secs., everything normal. imp

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Hey Imp, welcome to Stangnet.

The best thing for you to do is what is suggested above. This works for the '94-'95 mustangs as well. The surging idle checklist will help you find the exact problem.

Have you dumped the codes yet?

In the future you'll want to start a new thread when you have a question. The people that view this one only see the original poster's title and you won't get as many people to respond personally to your question that way.

Good to have you with us though.

karthief said:

I think this belongs in the tech section anyway.

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And yet.........

Dan2017 said:

The idle was searching from about 600 to 900 rpm, I replaced the IAC, and the idle has leveled out at about 900 rpm... until I turned the a/c. The engine runs fine without the a/c, but with the a/c on the idle wants to snuggle 550, and stalls coming down from higher rpm. The engine is stock except for. 1" spacer under the plenum. Any suggestions?

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You guys with idle/stall problems could save a lot of time chasing your tails if you would go through the Surging Idle Checklist. Over 50 different people contributed information to it. The first two posts have all the fixes, and steps through the how to find and fix your idle problems without spending a lot of time and money. It includes how to dump the computer codes quickly and simply as one of the first steps. I continue to update it as more people post fixes or ask questions. You can post questions to that sticky and have your name and idle problem recognized. The guys with original problems and fixes get their posts added to the main fix.

It's free, I don't get anything for the use of it except knowing I helped a fellow Mustang enthusiast with his car. At last check, it had more than 250,000 hits, which indicates it does help fix idle problems quickly and inexpensively.