NF V6.0 revs up when hot

[corkhead]

Hi,

My 89 NF v6.0 auto .. revs up when hot .. not always. but most times ... when idling will start reving to 2-3000rpm, then drop for a bit and rev back up .. goes up and down .. if u give the throttle a little jab normally drops it back down for a sec and then up again.

More often on stinkin hot days like today.

not sure what it could be ?

have replaced air filter, air sensor, injectors, new plugs, leads, rotor button and cap.

The car does have an old school dual battery setup.

Could it be something in the autochoke/throttle body or maybe oxygen sensor in exhaust ??? the other i was thinking is the dual battery .. if voltage drops (maybe not working right) would the computer rev the car up ?

any thoughts ...... would be great !

cheers

[Tas_Dean]

At a quick guess I would say that either the Throttle position sensor or the idle speed controller is on its way out. An auto electrician would be able to find the problem fairly quickly!

[corkhead]

thanks for the input

i have a complete engine, auto, t/case from another paj ....i rolled me last one .. kept the running gear !

so have been swapping bits hear and there .. the other ran perfect .. new engine.

so if i swap the throttle body it has all what you just mentioned ... might do that on w/e

cheers

[awbeattie381]

idle stepper motor for sure. mine had the opposite problem (twice). Mine was stalling rather than revving hard. Cleaning it out gave me a good 12 month run but then when it started again i had to get a reco'd one.

[corkhead]

ok ... i have now replaced the whole throttle body and still does the same thing ... revs up after a long/med run and when at operating temperate for no god damn reason at all ......

i have been told it could be voltage drop and then car compensates with high revs ???

any other ideas .... i dont really want to take to auto elec and get charged over the moon ..........

[-Scott-]

I've never seen the ISC up close and personal - is it possible to disconnect it and see if the revving problem goes away? You'll probably find the car won't idle at all, and I'm not sure what else this tells us, but it may help.

Its a long shot, but is it possible the temperature and O2 sensors are giving confusing signals. If the ECU thinks the engine is cold perhaps it's trying to boost idle and look for a rich mixture?

Hey, there's nothing like grasping at straws!

Scott

[Rossco]

Try disconnecting the battery for about 1/2 to an hour, this could reset the computer if there are any fault codes in it.

[corkhead]

thanks all for your input.

sometimes i dont think logically - if its got a problem when getting warm then i spose you should look around the temperature control/sensor area.

it was one of the temp sensors under the thermostat. Replaced and fixed st away.

Im glad i kept my running gear out of the last paj. !!

now of to neerim and go bashing today !!!!!!