94 mustang mysterious missfire
I have a 1994 mustang gt with 121,000 miles on it. It started acting up after I hit the exhaust on a bump in the driveway while backing up. The RPMs started bouncing around while it was trying to idle. I took it to the shop and they replaced the IAC valve. Once I got the car back the RPMs would raise when I pushed the clutch an let off the gas while shifting. It looks like there was a rubber plug on the TB that they left off. I covered it with electrical tape and that seemed to help. The other problem and the one that continues is that the car seems to cut out or misfire. It happens on the street and the freeway, and mainly when the engine speed is constant. I've replaced the spark plugs, spark plug wires, rotor and cap, and worn vacuum lines to carbon canister. I've also cleaned the MAF unit. I ran the codes and I got 111, 157, 158 on the KOEO test, and I got 90, 157, 998 on the KOER test. I figured the MAF was bad. I disconnected it and took it for a drive. It still cut out. Any ideas?