i have a problem with a N/A 1990 FC, when its outta gear it will go to redline but when u put it in gear and drive it and put a load on the engine it acts like its hitting the rev limiter at 4000 but u can press in the clutch and go straight to redline and no c/e light. i thought maybe switching ECUs would fix this so i borrowed my friends 88's ECU which wouldn't fit, (duh diff plugs). my only other guess is the coils, wut do yall think? please please please help me.

 

Things to check:
Sparkplugs, Plug wires, Coils
secondary injectors, injector connectors, grounds
TPS (not the setting, but the sweep)

 

your 5th and 6th ports could be stuck closed

 

You need to answer a question. If you are light on the throttle, and rev the engine up to redline while DRIVING, will it go relatively smooth to redline?

Or is this stumble/whatever only happening when you are hard on the gas? and hit around 4000 rpm?? And if so, if you stay on the throttle, does it keep going to redline. Is the stumble only at four grand and then more/less smooth out above that figure?

Try removing the vacuum hose from the boost/pressure sensor. Plug that line. Then drive the car hard up to redline. Question> did the stumble disappear?

 

Hailers beat me to it..