Mondeo, slow return to idle | Technical matters | Back Room Forum

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Wed 15 Feb 2006 12:50

Mondeo, slow return to idle - Reckless Engineer

Hi all. I own a 1999 V plate 2.0 zetec Mondeo, The only problem I have with it (other than the usual leaky rear lights and worn bottom-arm-bushes) is that it is a little reluctant to return down to engine idle speed. This usually occurs when using engine braking/coming down through the gears and can be a little worrying when the engine revs fail to drop below 1500-1750 rpm. This engine speed is then maintained for about 30 seconds or so, even after I have come to a stop and dipped the clutch, then it will slowly drop down to an idle speed somewhere between 800 and 1100 rpm. (the idle speed doesn't fluctuate once its got to idle).
I have checked the throttle cable to ensure it is running free with no resistance, and lubricated up all the joints/pins etc on the linkage but it still refuses to go straight back down to idle, and the rev-range it occurs in is almost always the same. Has anyone else had this problem? Is it an easy-fix or am I going to have to pay through the nose for a new e.c.u. ?
Thanks in advance for any help/advice.
Reckless Engineer

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Wed 15 Feb 2006 13:15

Mondeo, slow return to idle - jc2

Unlikely to be ECU;has the idle speed control valve been cleaned/replaced?

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Wed 15 Feb 2006 14:09

Mondeo, slow return to idle - Reckless Engineer

Erm. No.
I certainly haven't done anything with it, my attempts so far have been limited to ensuring the cable/linkages were free externally.
Could you advise on the best method for cleaning up the control valve (I would hate to take it off and break it/loose any tiny clips/springs that I didn't know about until they went pinging across my garage floor) then I can do it this weekend to see if it improves things.
Thanks.
R-E

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Wed 15 Feb 2006 14:35

Mondeo, slow return to idle - jc2

I don't know the exact procedure on a Mondeo-on my cars,they are front/top of the engine but I am sure someone else will;alternatively,Haynes.

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Wed 15 Feb 2006 15:56

Mondeo, slow return to idle - Number_Cruncher

One of the things that can cause this type of fault is if there is something stopping the throttle plate closing to its correct closed position. This can be either due to accumilated crud, or because someone has fiddled with the throttle stop.

This can cause the throttle position sensor to fail to report to the ECU that idle speed is required, and the ECU holds open the idle speed control valve, or fails to apply over-run fuel cut off - or both!

Cleaning out the throttle body, and checking that there has been no tampering isn't a big, or expensive job, and it is where I would start.

Number_Cruncher

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Wed 15 Feb 2006 19:12

Mondeo, slow return to idle - Dynamic Dave

See if Andrew Moorey's suggestion in the following thread helps at all:-

www.honestjohn.co.uk/forum/post/index.htm?t=21595

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Wed 15 Feb 2006 21:07

Mondeo, slow return to idle - Number_Cruncher

As long as the throttle is not being held open by muck or mal-adjustment, the re-learning procedure is fine. However, if there is an underlying reason why the throttle isn't shutting, resetting the ECU is a bit like applying lots of deodorant to disguise lazy hygeine habits!

Number_Cruncher

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Thu 16 Feb 2006 16:14

Mondeo, slow return to idle - Reckless Engineer

Thanks to all for the help and the advice, it is appreciated.
I guess all I need to do now is find the time to do it over the weekend.
Thanks again. R-E

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