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Flivoless

Throttle body problem?

8 posts in this topic

I have had my SC430 (6 speed) for a few months now and have a problem which I hope some of you cleaver people may be able to throw some light on. The engine idles smoothly at just under 800 rpm but when coming off the throttle at say 40mph for this example (but it's the same at any speed) the revs stay at 1100-1200 rpm so the car does not slow down - taking some 200m reduce speed to 30 mph. However, if the brakes are applied (necessary!) firmly, the revs drop to the normal idle level. Is the throttle body the likely culprit?

Any help will gratefully received.

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If the brakes are applied, just enough to make the brake lights come on, is that enough to make the revs drop?

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Thanks for your post Colin. "touching" the breaks doesn't seem to make a discernible difference.

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Once the brakes are applied the gearbox should disengage the lock-up torque converter (if it is engaged) so it doesn't sound like that is the isuse.

Do you experience the same behaviour with AC on or off?

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I'll try this Colin

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Hi Colin, I have now tried with Aircon off but no discernible difference. Also tried in PWR and Norm modes but no difference. It's as if the wheels are driving the engine. Throttle position monitor / gearbox?

As a matter of interest and to, hopefully, increase my knowledge, what was your thoughts behind the Aircon on and off?

Regards

Marc

 

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Hi Marc

Aircon increases the engine load, so to avoid the idle speed dropping too low the ecu increases the throttle opening to compensate, although it overcompensates by design so you have an increased idle with the ac turned on.

I'd start by looking at the throttle body, that probably needs a clean, especially the butterfly, and also give the MAF sensor a clean. (not sure what has happened to the photos, I'll see if I can fix that.

 

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Thanks for this Colin. Have to say that in all other respects the car runs very well indeed. It's now done 70k miles id that helps with possible reasons for the problem.

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