High tickover on over-run
Discussion
I have a problem with my Chimaera 450 (97 model which I bought in March 2002) which happens quite often on over-run.
When I lift off the accelerator the car seems to hold part throttle. If I dip the clutch at this point the engine revs drop to about 2000RPM then slowly decrease to tickover (8-900RPM). If I'm stopped at traffic lights etc the engine won't settle down to idle for several seconds (up to 30 seconds).
The engine temperature etc. seem to have no bearing on when this happens - it just does it sometimes and not others. Could this be the stepper motor?
I noticed that the ECU has '5 litre engine' printed on it, but the local dealer said this was nothing to worry about (but he would say that I suppose).
Has anyone suffered from this problem? If so what can I do to cure it?
>>> Edited by Plipton on Wednesday 16th October 09:12
When I lift off the accelerator the car seems to hold part throttle. If I dip the clutch at this point the engine revs drop to about 2000RPM then slowly decrease to tickover (8-900RPM). If I'm stopped at traffic lights etc the engine won't settle down to idle for several seconds (up to 30 seconds).
The engine temperature etc. seem to have no bearing on when this happens - it just does it sometimes and not others. Could this be the stepper motor?
I noticed that the ECU has '5 litre engine' printed on it, but the local dealer said this was nothing to worry about (but he would say that I suppose).
Has anyone suffered from this problem? If so what can I do to cure it?
>>> Edited by Plipton on Wednesday 16th October 09:12
It does sound like the stepper. I had a similar intermittent problem on my V8S - they can get fouled up over time and stick. Its easy to unscrew it from the plenum and see if the piston moves in and out, but be gentle - £80 or so to replace! If it is sticky then degrease with a suitable solvent and see if it frees up. Mine was solid and I had to replace it during its recent re-build.
>> Edited by keithyboy on Wednesday 16th October 10:25
>> Edited by keithyboy on Wednesday 16th October 10:25
Thanks Keithyboy.
At the risk of sounding like a complete dumb@ss can you tell me where the stepper is? (Have only worked on aircooled VW engines and old pintos, you see, so the V8 is a bit, er, challenging) If you have a picture it would be very helpful.
Also do you know where the rad thermostat is located - I think mine's stuck open.
Thanks
Plipton
At the risk of sounding like a complete dumb@ss can you tell me where the stepper is? (Have only worked on aircooled VW engines and old pintos, you see, so the V8 is a bit, er, challenging) If you have a picture it would be very helpful.
Also do you know where the rad thermostat is located - I think mine's stuck open.
Thanks
Plipton
Plipton:
Had away yer wuss! It's only an engine! Get in there and look at the thing, soon it all makes sense.
The thermostat housing is at the front of the engine, bolted to the front of the inlet manifold. There should be a large-bore pipe leading from it to, er, the radiator top connection. You might find the distributor restricts access to the bolts a tad, depending on its position (in a rotational sense).
Ian
Had away yer wuss! It's only an engine! Get in there and look at the thing, soon it all makes sense.
The thermostat housing is at the front of the engine, bolted to the front of the inlet manifold. There should be a large-bore pipe leading from it to, er, the radiator top connection. You might find the distributor restricts access to the bolts a tad, depending on its position (in a rotational sense).
Ian
Hey Plipton,
this happens to my 97 Chimaera too. Sometimes it holds revs when you dip the clutch, other times it even revs up when you press the clutch!
Anyone know what sort of rev should the engine should hit when it starts up from cold, without accelerator pressed? Mine seems to go crazy - neighbours are probably loving it!
What does this stepper unit do then, act like a hand throttle and add to the throttle pedal input? Sorry but only worked on carbs before.
Cheers all,
Matthew
this happens to my 97 Chimaera too. Sometimes it holds revs when you dip the clutch, other times it even revs up when you press the clutch!
Anyone know what sort of rev should the engine should hit when it starts up from cold, without accelerator pressed? Mine seems to go crazy - neighbours are probably loving it!
What does this stepper unit do then, act like a hand throttle and add to the throttle pedal input? Sorry but only worked on carbs before.
Cheers all,
Matthew
Stepper motor is also known as the idle speed control valve.
Its function is to bleed air past the throttle plate so raising the idle speed when say switching on an electrical load, and lowering the speed when the load is removed.
Its controlled by the engine management sytem and can compensate for hot/cold starts etc so that the engine maintains a smooth and consistent idle speed.
Hope this helps ya.
Its function is to bleed air past the throttle plate so raising the idle speed when say switching on an electrical load, and lowering the speed when the load is removed.
Its controlled by the engine management sytem and can compensate for hot/cold starts etc so that the engine maintains a smooth and consistent idle speed.
Hope this helps ya.
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