I just recently (6 months or so) got a 5.0 Tpi Formula this thing had ran like crap since day one. After repairing several jury rigged wiring issues and a couple sensors. I have the same nagging problem High Idle and when warmed up to temp car just falls on its face. When its cold it runs strong. I have changed IAC twice set timing (was 10 degrees retard when i got it cause the guy said he dont need no timing light) new temp sensor etc. Kinda lost and wondering if anyone else has had this kind of issue.

 

check EGR, Fuel pressure, and vacuume, then get a garden hose spray a light stream of water around on the intake ( with special attention to all gasket zones) listining for the motor to speed up more, you will know when you find it. do you get a SES light with the key on - motor off? if not? fix that, then check your codes.
Yours does not have the 9th injector - so that is not an issue. check your vacuum line to the brake booster, and make sure the PVC valve rattles.

start with these let us know?
could be a bad ECU i have seen that on my own car.

 

Well I think i Might have found something on it . The Iac is never closing i took it out and tried the procedure for setting it and the damn thing never moved at all you could feel the little motor humming but it never moved forward makes me wonder if one of the wires isnt hooked up wrong on the IAC making it go backwards instead of forwards. Tried 2 different Iac both same thing completely bottomed out. So aggravated wish the idiot i bought it from hadnt thought he was a wiring expert.....