Ford Repair: Engine Performance, throttle position sensor, moreno chico

Question
Steve,

I own a 1990 DPS Ford Mustang with a standard transmission and 5.0L engine. The engine started cycling between 600 to 900 RPM. I, then, cleaned the throttle body and re-installed it. It ran fine until last weekend. Then the engine after starting would not idle and die. I would sit in the vehicle and hold the accelerator at about 1000 RPM until the engine got warm. Then it would idle but it idled rough like I have a full race cam in the engine. When driving it to Dallas last weekend, the engine RPM would not decrease when shifting from one gear to the next. The when at a stop light the engine idled at 1500 RPM. I tried to pull the accelerator pedal upward with my foot but was not successful.

Today, I changed out the throttle body sensor thinking that it was the problem. I also took off the throttle body and cleaned it out again along with changing out the air filter. Unfortunately, the engine is still doing the same thing. One good thing is that the engine doesn't cycle as badly as before. It cycles from 600 to about 800 RPM.

Please let me know what I need to do to fix this problem.

Thanks for your time and effort.

Sincerely,

Chico Moreno  

Answer
Chico-

  Sounds to me like a problem with the throttle position sensor (or TPS).  They're easy enough to adjust if you're familiar with a voltometer.  You just need to make sure the TPS reads around 0.90 volts or so at idle.  If it tips over 1 volt at idle, it'll start to mess with your idle speed.  Hope this helps.

Steve