Actually, the idle speed motor should be the last thing on the list of suspects. A red-hot exhaust manifold, (or catalytic converter) tells you that's where the fuel is burning instead of inside the cylinders where it will produce power. If the catalytic converter has been removed, the front and rear oxygen sensors are going to read exactly the same thing. The Check Engine light should be on and there should be a fault code related to "catalytic converter efficiency". Unfortunately any tests the Engine Computer performs that use oxygen sensors as a reference will be suspended, so some problems may not be detected or set a fault code to direct you to where to start.
One thing to consider is valve timing. A jumped timing belt will cause low power and late fuel injector pulses. A vacuum leak will cause high idle speed with no corresponding increase in power.
Once vacuum leaks are ruled out, have the diagnostic fault codes read and recorded. Those will indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. The people at many auto parts stores will read the codes for you for free.
Monday, July 20th, 2015 AT 8:47 PM