Would a bad TPS cause an unstable idle?

With it connected the idle is erratic and then the SES light comes on and then the idle smooths out. The code retrieved is a code 33. I have a '91 3.1L w/ a MAP sensor. I can find no vaccuum leak. When I disconnect the TPS and start the car the idle is not erratic. Also sometimes the ECU does not seem to respond to throttle changes, ie., tap the throttle to rev the engine and the RPM does not go back down to idle speed and I have to wiggle the throttle mechanism. When driving sometimes and I apply a slight pressure to the accelerator pedal to speed up a little bit the engine starts vibrating like its leaning out.

Could a TPS be bad but not enough to alert the ECU?

KeithM

 

Is your MAP sensor connected?? Both the electrical connector and vacuum line? Can you hear any vacuum leaks?

 

tps can cause bad idle-you have a map sensor code-key on engine off you should have under 4.8 volts at the signal wire usually lt.green-ck. with dvom over 4.8 usually indicates replacement is required-are you sure of no vacuum leaks-

 

Well with the TPS disconnected the idle is stable. And yes the MAP sensor is connected and the vacuum line to it is connected also.

I disconnected the vacuum line one at a time and plugged the ports and the idle was still bad so I think that more or less ruled out a vacuum leak.

KeithM

 

A lonnng time ago, Hot Rod had a little one-paragraph written up (in their tech questions section) about the TPS. They said that sometimes, if water gets onto a TPS, you'll get an unstable idle.

Have you pulled the diagnostic code from the computer yet? What does it point to?

 

I just get a code 33 when the idle gets to low.

KeithM

 

you are going to get that code if the idle speed drops and causes manifold vacuum to fall below what the ecm thinks it should be seeing-the map sensor is probably not the prob.only a symptom of whats really happening.hows the egr valve- leaking internally? power brake booster-pinch the hose note rpm change. take a matchbook of something and fit it between the throttle lever and tps arm to get the tps off the bad spot(if any)

 

I replaced the TPS and that fixed the problem.

The idle doesn't wander all over the place now.

KeithM

 

Congrats on the fix -- and thanks for letting us know what happened!!