Ok this is my first mustang! I got it about 2 weeks ago and it has a loping idle like a cam, the engine light is on sometimes, goes off, and comes back on! The car runs good when the engine light is off. Sometimes the car will hesitate when i get on the gas(usually happens right after a shift to say 3rd gear and getting on an on ramp, but has happened just cruising in 4th and 5th gear aswell.) Maybe loses fuel pressure for a split second. Now when I'm at a traffic light the car stays running but the idle is up and down between 600 and 900. If the engine light is on and I tap the gas the idle drops way down and wants to stall, so at lights I have to rev it up before I can start to let the clutch out or else it will stall. When I do finally get it goin it takes off for a split second too. If the light is off she takes off just fine. When i come to a traffic light sometimes the rpm goes to about 400 and sometimes will stall. I haven't done any of the mods that the car has but here's the list. It has a msd cap and coil, Ford racing wires, had autolite plugs but I put motorcraft in and tapped to .052, has headers not sure what kind, x pipe not sure what kind but no cats, flow masters, cold air intake, the fuel pump and filter are new, not sure about the regulator but it looks new and there's no fuel in the vacuum line. He had the timing advanced to 30 degrees so I backed it down to 15. I set the idle and iac, and i did a decarb. The iac and the Tps look new. I also fixed 1 exhaust leak between the header and the x pipe, o2 sensors look kinda new but not positive. Sounds like there is another leak somwhere but I haven't found it yet. I changed the t stat and the ect but i didn't change the coolant temp sender. Distributor doesn't look like it has been changed. I'm getting a code reader on monday to see what the light is for, until then I figured I would give the forum a shot to see if this is a common go to part or if there's any tricks to put me on the right path. Btw the car runs a lot more steady but the hesitation seems to happen more since I retarded the timing and set the idle. And the guy i bought it from said he cleaned maf but didn't replace it but he said it ran worse after he did that. Maybe he f&@#ed it up.
