Erratic Idle Problems - FFCars.com : Factory Five Racing Discussion Forum

AyRoMoDa · 07-02-2012, 03:17 PM

I have had a new issue pop up in the past few days and need some advice on how to solve the problem. I have a donor '87 302 EFI with ~57K. Starts and runs fine, idles at ~ 1000 rpm. Lately after reaching temp the idle will surge and when coming to a stop the engine will surge and will die. Starts right back up but I have to feather the throttle to keep it running. This is occurring only after it is at temp. My limited knowledge is of no help figuring this one out.I was planning to go the Summer Run in Lake George, NY in a couple of weeks but I don't think I want to chance having an issue on the road (especially since the trip is doubling as an anniversary present). Any advice of what could be causing the problem?Thanks in advance,Paul

Wade Chamberlain · 07-02-2012, 07:31 PM

I'd start by checking the codes...that may point you in the right direction. Could be a vac leak too.

lbperry · 07-02-2012, 08:18 PM

First thing that comes to my mind on a surging idle is the Idle Air Controller (IAC). I had a similar problem and had to clean all the carbon buildup out of it and then I think I replaced the elecronic part of it too. But Wade is right, the codes would probably confirm that or point you in the right direction.
Good Luck,

AyRoMoDa · 07-03-2012, 03:26 PM

Thanks guys.

I don't have a reader so I couldn't easily check the codes. I inspected all the vacumn lines and couldn't find anything obvious so I looked at the IAC and it was all gummed up, so I replaced it and I'm good as new.

Thanks again,

Paul

mcmccu · 05-20-2013, 06:24 PM

My problem was sometimes after the car was warmed up the idle would surge. I have a stock 1987 5.0 HO. Sometimes it would surge 1100 to 500. Sometimes a few hundred rpm. Sometimes not at all. I couldn't fix it. Over many years 5 highly recommended expert 5.0 mechanics worked on the car looking for vacuum leaks, replacing the TPS, idle air control motor, and other parts. No change other than to my bank account. I thought about switching from speed density setup to mass air flow. I considered going carburated. In March radiator fluid started coming out the sidepipes. I took the engine out and had it rebuilt. NOT a blown headgasket. The bolt on the right front of the lower intake was finger loose. The water jacket next to it was leaking fluid into the plenum. This will ruin your idle. The car now runs PERFECT.

Here's a list of other things to check.
Help me create the "Surging Idle Checklist" | Mustang Forums at StangNet