2000 rpm! from start!

[myles77]

any ideas when i start my 1996 chim it ilde's at 2000 revs straight away! from a cold start ive cleaned the stepper motor, an tried unpluging sensors to see if any change in revs ,reseting the ecu each time. when i disconnect the air flow meter it drop's too 1500 revs.replace this but no joy.that leaves the throttle pot sensor but not sure how too test that ? the throttle cable looks to be fine and retracting ok with plenty greese on the springs,it seems to me its more mechanical than a sensor any clues?

[anonymous-user]

Mine did this it was the pedal catching on the carpet in the footwell...

[myles77]

i wish it was that simply hey ,il check that as well.

[blitzracing]

Air leak into the plenum some where! This could be plenum base seal or trumpet base seal (only gasket compound), split rubber hose, split stepper motor casting, or air getting past the motor, or missing screw(s) from the preheat plate below the plenum. I assume the throttle plate is fully closing? (Remove the air intake pipe to the plenum and have a good look). Clamp off the rubber air feed pipe to the stepper and see what it does. If it sticks high, its nothing to do with any sensors, stepper motor movement or the ECU.

[taylormj4]

This be the stepper couldn't it blitzracing ?
You're the expert but I thought that if you disconnected the stepper motor with engine off and then restarted, the revs were about 2000rpm due to the stepper being wound to its stop on engine stop (the buzzing noise). If stepper/wiring to stepper has failed with it on its stop, couldn't this cause the high revs ?

[MikeTVR]

See my response to the topic 'Random Revs'

[blitzracing]

taylormj4 said:

This be the stepper couldn't it blitzracing ?
You're the expert but I thought that if you disconnected the stepper motor with engine off and then restarted, the revs were about 2000rpm due to the stepper being wound to its stop on engine stop (the buzzing noise). If stepper/wiring to stepper has failed with it on its stop, couldn't this cause the high revs ?

I was making the probably rash assumption that the stepper would work after a clean...., but anyway thats why I ask for the hose to be clamped as a test to be sure.

[myles77]

i clamp off the air supply an sure enough the revs died so went back to the stepper motor ,which was fully wound in. so plug it back in an held it in my hand, turn the car over whilst coverin to hole where it should go to see if the stepper would work (being the car reving at 2000 rpm the ecu should send pulse's to the stepper to close off the air ) there was no movement from the stepper at all. is this meanin a new one or could it be the wiring ,how can i test ?

[blitzracing]

myles77 said:

i clamp off the air supply an sure enough the revs died so went back to the stepper motor ,which was fully wound in. so plug it back in an held it in my hand, turn the car over whilst coverin to hole where it should go to see if the stepper would work (being the car reving at 2000 rpm the ecu should send pulse's to the stepper to close off the air ) there was no movement from the stepper at all. is this meanin a new one or could it be the wiring ,how can i test ?

You have already tested it then, if you have it in your hand, and the car is sitting at 2k rpm, the stepper cone should move outwards in stages to try and slow the idle (which obviouly it cant!.) Sounds like yours is stuck in the retracted position. I do have a test box to check them off the car if you want to pop it in the post. You could put a test meter across any pair of the 4 pin connector, and you should get voltage readings as the ecu provides stepper pulses. These are 12 volt pulses, but you may not get a fully sensible reading from a DVM because of the pulse rate, but it should show something.