Weird Idle Problem After Missing 3rd Gear.

[JBman93]

Ok guys I have an 89 GT. Cars idle was fine. Cold starts were good and only surged once in awhile after driving awhile and stopping at stops lights but didn't do it all the time. The car didn't have 02's so I put in a brand new harness and 02's. Started the car up and it drove much smoother. Then after 15 min of driving I punched it from a stop light racing a 370z and ended up missing 3rd gear and once I felt the rpm's shoot up I let off the gas then put it back in 3rd. The car immediately started driving weird like sputtering a lot. Drove it home and now every time I start it up the idle shoots up to 2000 rpm's and stays there? Will not come down unless I push in the clutch and hold it there. As soon as I let off the clutch it shoots back up. When I unplug the IAC it goes down to normal but stalls when driving. Cant even drive the car now. I bought a Motorcraft IAC and nothing changed. Replaced ECT and ACT temp sensors (super old) and still nothing. Installed new BAP sensor and installed a brand new fuel injector harness and cleaned female 10 pin connectors and still nothing. Checked all injectors and they are good. Put a new upper intake gasket in and that didn't do anything. Fuel pressure is still at 40 psi. For the sputtering problem I replaced plugs, wires, fuel filter,cap and rotor. It got better but still not perfect. But as far as the idle doing what its doing I'm at a loss. Just because I got on it and missed 3rd it does this?? Like I said, everything was pretty much good before this.. Any help would be greatly appreciated.

5.0l, Cobra intake manifold, 24lb FR injectors, 70mm TB, calibrated BBK maf, BBK longtubes, BBK CAI fender, BBK X pipe, MAC pro dumps, Cam(not sure which one) 1.72 rocker arms. MSD box. Electric fans.

 

[jrichker]

You guys with idle/stall problems could save a lot of time chasing your tails if you would go through the Surging Idle Checklist. Over 50 different people contributed information to it. The first two posts have all the fixes, and steps through the how to find and fix your idle problems without spending a lot of time and money. I continue to update it as more people post fixes or ask questions. You can post questions to that sticky and have your name and idle problem recognized. The guys with original problems and fixes get their posts added to the main fix.

It's free, I don't get anything for the use of it except knowing I helped a fellow Mustang enthusiast with his car. At last check, it had more than 159,000 hits, which indicates it does help fix idle problems quickly and inexpensively.

 

[7991LXnSHO]

Wow! That was a lot of work to not ask for help first. Look up the list, read it a half dozen times before running all the tests, post the results and codes, then have a nice running car.