I've built and owned at least ten mustangs all early 90's though and had zero driveability issues. This is my first sn95 I picked up couple months ago and about from the jump it stumbles down low, after chasing around the problem it got starting issues...ended up being the dizzy. Ok bout a week later I got the same surging I see alot of you have, checked everything, tps,cleaned IAC, cleaned maf,replaced maf, set base idle, adjusted set screw, tried a different ecm etc. etc. I was ready to burn the damn thing it would surge to 2000 rpm no matter what I did!!! :BangHead: I've been a tech for almost 15 years and now work for a large family owned auto salvage yard so I know how to track down issues but I almost lost it on this one!! Lol...today I'd had it my brakes were smoking by the time I got to work today as the rpm's reached 3000 today the whole 20 minute drive!! so me and an old timer from work did the most simple tests no scanner, no voltmeter, just used our hands, pulled intake tube started car covered throttle body died instantly, took off IAC motor started car covered that with hand car died so we eliminated the idea of a vacuum leak. So we ended up taking a pepsi can poking two holes in it with a test light trimed it to cover the hole closest to the front of the IAC and screwed her back down with IAC plugged in. fired her up and what would ya know ....she idles smoothly at about 700 rpms, doesnt stick,no more surge, nothing but a smooh idle!! A band aid fix I know but after three weeks and trying any and everything else all of you suggested, It will stay there until next year when I finish rebuilding my 4 valve for a turbo project I plan....did I mention no CEL either since the IAC is still plugged in. :headbang: