High engine rev at start up

[zagato]

Hi Guys,

 

I need some help with my engine problem.  I have a 1990 TC with a 3 litre V6.  Last week when starting the car the engine immediately revved up to 4500 rpms and will not return to normal idle. The fault code read 14 which would indicate the MAP sensor voltage is too low.  However I checked the voltage and it read at 4.8 at the output.  I went ahead and changed the MAP sensor and any vacuum hose that showed any sign of cracking.  I also changed the throttle position sensor and I still have the high revving when starting the engine.  Does anyone have an idea of what the problem is?  I am open to any suggestion.

[Hemi Dude]

It would seem that you have some large volume capacity VACUUM HOSE disconnected somewhere.

Are you telling us that this occurred all by itself? How long has the car been parked and un-started?

 

The AIS motor, mounted right near the TPS could also be the problem. Have you checked it? 

As a test, remove the rubber air intake hose attached from the air cleaner to the throttle body. Feel inside the throttle body for a hole, use your finger.

Did you find it? Remember where it is.

OK, now start the engine and return to the throttle body and plug that hole you found, in the throttle body, with your finger.

The engine should slow down and possibly stop running if the AIS is stuck open. If it does, replace the AIS motor.

[zagato]

Thanks Hemi, it was the AIS!