Hey guys, I'm a newbie to the forum so this is my first post. I've got an '04 Mach 1 with a 5-speed, 4.30 gear, Bassani X-pipe (with cats), Bassani after cat, and a K&N Filter in the factory box, and a Speed-cal box for obvious reasons...haha. Now to the hard part. My problem is that occasionally when I push in the clutch the engine will die, the other times it will idle at 400 rpm, and occasionally surge to 1500 to 2000 rpm until I blip the throttle and then it will slowly idle down. It seems to do it more on hotter days when I'm running the AC but it's not always. It also seems like the hotter it is the more it does it. I have checked and cleaned the MAF and the Idle air controller, both looked clean. I have also looked for frayed wires but have yet to come across anything, nor have I found any vacuum leaks. Any help would be greatly appreciated!

Thanks!
Adam

 

Stock tune? If you have a tuner...any changes in settings? One possibility is that the idle is low and the racing idle is the computer trying to compensate. Using aftermarket intakes w/o retaining the MAF screen causes similar symptoms. Your's is still in, right?

 

Has the fuel filter been changed? If not, you may want to do that before you go chasing things too much further.

 

It's got the stock tune still (unfortunately). I replaced the fuel filter last year to no avail.

 

Is it throwing codes? Mine did a similar thing about 4 months ago, I went back to factory tune and it hasnt done it since. I also got way better gas milage after that lol.

 

It's not throwing any codes and as far as I know it's still got the stock tune. It only have the gears and catback when I got it. Any way of checking it (besides going to ford)? The first (and last) time I took it to a dealership for work they took it out and did a burnout in it. Of course I couldn't "prove" it, but the evidence was on my bumper. I guess like most mustang owners i'm a little protective of my car..haha.

 

I say replace the IAC valve. it may appear clean but that doesnt mean it is not sticking. that would most likely be the issue. while running the A/C mine has gone down to about 400 or so before but it has never died on me. its just the ECM changing idle and fuel due to load of the A/C typically.

 

I would have killed somebody.

 

Since I had the car in the air this weekend I went ahead and replaced the fuel filter again. I can't believe how nasty it was! Clean fuel poured out of the outlet, but there was some thick brown sludge that come out of the inlet when I drained it. I must have gotten hold of some bad gas. So I'm hoping that was the problem (keeping fingers crossed). The car was definitely more responsive when I took it around the block yesterday. It's supposed to get hot here this week so I should be able to see if that is in fact the solution. I'll keep ya'll posted.

Thanks again for all of the suggestions!

And Cody, I was pissed! Needless to say my car will never be at that dealership again.

 

Ok Guys, I drove the Mach to work today (close to 100 degrees and probably 90% humidity) and the car didn't cut off but it came darn close! It dropped to 350-400rpm at one point and i more often than not I had surging at idle around 1500-1800rpm. any more suggestions?