Rough Running 93 Mustang

I'm trying to help a friend with her car, 93 Mustang V-8 with EFI.

This morning I did a test drive from cold start. I would describe the symptom as what we used to call an " off idle tip in" problem. Severe hesitation during a light tip-in. Seemed just a little worse when cold, but is still substantial after several miles of warming up. Leaving a stop requires finesse or it stumbles to the point it feels like it will stall. Did stall yesterday in traffic with teenager driving. It does idle a bit rough even when warm. With more aggressive acceleration from stop this does not happen. Seems to run pretty smooth at cruising speed.

This is a high mileage vehicle with minimal routine maintenance. I know that many things could cause this symptom, but I suspect the throttle plate is not closing properly at idle, and the computer is trying to compensate poorly with the idle air by-pass, causing the problem.

Any ideas. Thanks in advance, Joe

 

Do you get a check engine light? Pull out any codes found on it and let's start there.

See if the IAC has carbon in it. Get the proper Ford cleaner and clean it out and see if that helps things.

 

I was told that check engine light has not come on. Plus, battery was replaced two weeks ago, so codes were erased. ( driver admits that tip-in problem has been happening for months...,)

thanks, will clean IAC first

I have just learned that car will be going to shop Tuesday. Other than these suggestions to tell service writer, do you have any other thoughts..???

 

Err, trade it for a GM product. Lol, ok really

Pull the codes anyhow, to see for a giggle if you get anything. Clean the throttle body and see if that helps. Look for any vacuum lines that are frayed or missing/damaged.

Idle surge on most Fords is a bad IAC. Common problem after a lot of mileage.

Can't remember if this thing has a mass air flow sensor or a MAP sensor. If MAF equipped make sure no air tubes (rubber boots) have cracks in them or that there isn't gunk on the inside of the MAF near the hotwire/sensing wire. If you find any (if so equipped), CAREFULLY clean it with electronics spray and see if that helps.

Also, if the vehicle has not seen a tuneup in a while, it's time. My cousin's Taurus came to my house the day we did the tuneup running on 4 and 1/2 cylinders. Lol. It left running on all six about 2 hours later

 

thanks once again, Joe