I am looking for a little help with my 95 Mustang GT, great little car to run to work and back, but since I purchased it a few months back it has a weird surge at idle when it's in drive. It doesn't happen all of the time, but seems to be frequent enough to be a issue and sometimes it will outright stall. I bought it with 100,000 miles and I am pretty sure it sat for a while. I have done the following and it has really helped with MPG and overall the way it runs.

-changed plugs, wires, distributor (complete), coil
-Timed it at 10 degrees with spout removed
-swapped out fuel filter
-cleaned IAC (thinking I should just replace it)
-cleaned TB and upper intake (I removed the upper and used big pipe cleaner with carb cleaner)
-ran some ford fuel injector cleaner through in at least 5 tanks of gas.
-bumped up the timing to 13 degrees and am now running 94 octane which has seemed to help.

It idles at about 700-750 in park and about 600 in drive.

Any ideas would be appreciated, as my wife is now afraid to drive the car since she almost rear-ended a car when it surged bad. I am thinking IAC and replacing the injectors. I was holding off on the injectors until I had Builts 42#er's in my truck and just put the 19's out of the truck in the car. But that might not be until after the holidays. Like I said it doesn't happen all the time and if I disconnect the battery it seems to be good for a week, then goes back to doing it again.

 

I had a friend with a simular problem turned out to be he needed a new upper intake gasket. Vacuum leek..

 

When I first got the car, the HVAC didn't work and it was always stuck on defrost. found a broken Vac line and fixed it. I checked the rest of the vacuum system at the same time, couldn't find any other leaks. I replaced the gasket between the upper and lower intake when I pulled the upper off to clean it. I will have another look to see if I pinched anything. I also cleaned the MAF and IAT because they were really dirty, almost like it didn't have the air filter installed properly.

 

most likely iac.

 

As an update, I brought the car to work this mourning, and it's acting up way more than usual. the only real change between yesterday and today is the fact that its pouring rain out today. I am wondering if a wet air filter could be causing a extra restriction. Any ideas.

I am picking up a IAC after work, but the rain will have to stop for me to change it.

 

i dought the filter got wet but you never know. even though theres no cel i'd get it checked out. KOEO and KOER tests are required to get the codes out of the obd1 systems. it may be the maf sensor.