1.25l Zetec-S over revving - what next?

In message , Tony Brett writes

It is a characteristic of these engines to keep the revs ups slightly as you are slowing down, in anticipation of you pulling away again. When you have been at a standstill for a second or two, the engine should drop to its normal idle of 750-850 rpm.

The EEC gets its information from the VSS (speed sensor) and the fact that your engine doesn't over rev when you disconnect this, or when you are at a standstill would suggest that this is your problem. Have you tried resetting your EEC? To do this you disconnect your battery and leave it for 30 minutes before reconnecting.

I believe it also serves as an anti-stall technique..

(To the OP) How long does it over-rev for?

I did reset the EEC after the new ICV but not after the TPS. I guess I should try that just to eliminate it.

Thanks,

Tony

Well it's hard to measure because the over-rev stops as soon as the car comes to a halt and I'm not in the habit of costing for ages with the clutch down or out of gear!

But I have tried some tests and I can coast for a good 100 yards without the engine showing any sign of reducing it's speed below about 2000-3000 revs. But as soon as I bring the car to a halt with the brakes the revs then drop back to about 900 within a second or two.

Tony

The anti stall increase in revs etc is a feature of the ECU, but it should not be over 2000rpm!

I'd have another good look at the TPS, and its throttle closed voltage (lower the better- under 0.7v, but go too low and it'll stall)

Tim..

Thanks Tim.

Ah - I didn't know it was possible to measure these things. Is there a wiring diagram available?

Thing is though, if it was the TPS then surely the over-rev would continue even after the car had come to a halt?

Many thanks,

Tony

DVM between pin 2 and good earth with ignition in Postion II, engine stoppped.

No. Bascially the ECU is just overcompensating with revs whilst its seeing the vehicle is in motion. (signal from VSS)

Tim..

OK- have now done that, and checked that the TPS is fitted correctly. Problem is still there. If I start the engine and let it idle with the TPS removed but connected and simulate throttle movement with a screwdriver on the TPS, the revs pick up and then there is a noticeable delay in them dropping again after I have let the TPS move back to throttle closed postion (the vehicle is obviously stationary when I do this!)

Experimentation shows that car will effectively drive itself at 30mph in 3rd gear on the flat so something's going on!

If I stop on a hill with the engine idling, clutch disengaged, then let the car roll down the hill (without touching the gas or engagiing the clutch) the revs start picking up all on their own as the car gathers speed. It only needs to be doing 5-10mph to get the revs up to c. 2k. Help!

Should I change the VSS now? Or give up and go and see a nice ford technician?

Tony

No, its doing exactly what it should be, but doing it too much. You should only see 12-1500rpm with the car coasting.

I suggst you also check *very* carefully for any vacuum leaks (including the brake servo- clamp the hose) around the inlet manifold which is letting in extra air.

Tim..