Hey guys this is my first post here, tell me how I do. I have a 1998 GT that I purchased with 111,000 miles. It has about 114,000 on it now. Has a few mods: CAI, Bassani catted X pipe, 4.10 gears, short throw shifter, and that's about it. Since I've had the car, it has had a slight missfire at idle. When it first starts it is fine, but when it drops down to idle speed it misses every few seconds. No CEL has been thrown since I've had the car. The only other noticeable thing is when I am in a higher gear, such as 4th or 5th, and I let off the throttle (so it is decelerating or engine braking) within a few seconds it feels like fuel is cut to the engine. If I push the clutch in and rev it quick like I am going to rev match, the engine sputters a bit before it revs up. Also, it feels like the car takes longer then it should to crank. Instead of like 2 or 3 cranks it is about 4 or 5. This is all the time, even when warmed up.
Now, all the stuff I have done to fix this:
New plugs and wires: First put in motorcraft copper plugs gapped to factory specs with Ford Racing wires. This did not help. Later I also installed NGK TR6 (One step colder) plugs gapped at .040. This did not change anything.
New coil pack: One of the coil packs appeared to be a newer OEM motorcraft unit. I replaced the older one with the same newer OEM motorcraft coil pack. Did not change.
New IAC: Almost seemed to run worse with a new Duralast IAC.
Cleaned MAF and installed new K&N filter: Didn't change.
New fuel filter: The old filter seemed dirty, so I installed a new one. This did not change anything.
Cleaned throttle body: The throttle body plate and inside of the plenum seemed very black, so I removed the throttle body and cleaned it. This significantly helped the idle, and also helped with the weird deceleration issue.
Now I am at a loss at what to do. I am going to be testing fuel pressure, because I think the fuel pump could be a problem as well. I am also going to put back in the stock heat range spark plugs gapped at factory spec. If anyone has any ideas as to what the issue could be, please respond. I just want to enjoy my car!
Now, all the stuff I have done to fix this:
New plugs and wires: First put in motorcraft copper plugs gapped to factory specs with Ford Racing wires. This did not help. Later I also installed NGK TR6 (One step colder) plugs gapped at .040. This did not change anything.
New coil pack: One of the coil packs appeared to be a newer OEM motorcraft unit. I replaced the older one with the same newer OEM motorcraft coil pack. Did not change.
New IAC: Almost seemed to run worse with a new Duralast IAC.
Cleaned MAF and installed new K&N filter: Didn't change.
New fuel filter: The old filter seemed dirty, so I installed a new one. This did not change anything.
Cleaned throttle body: The throttle body plate and inside of the plenum seemed very black, so I removed the throttle body and cleaned it. This significantly helped the idle, and also helped with the weird deceleration issue.
Now I am at a loss at what to do. I am going to be testing fuel pressure, because I think the fuel pump could be a problem as well. I am also going to put back in the stock heat range spark plugs gapped at factory spec. If anyone has any ideas as to what the issue could be, please respond. I just want to enjoy my car!