Mondeo idle issues!

[GRIFFLG]

Hi

After a bit of advice as not getting anywhere though have taken my car to two mechanics..

My mondeo has started to have an intermittent idle issue where the the revs will go up and down sometimes cutting out. If I turn the engine off or if it cuts out and I restart the problem goes away.

Happens now and then it is never consistent and the fact I can turn the car on and off seems to reset the problem is baffling.

No faults come up on any diagnostic testing on the ECU and no pending codes either.

One mechanic mentioned the EGR value or crankshaft sensor another said would need to smoke test to check for leaks. Looking around it looks could also be fuel related..

I don’t really want to spend much more on the car and it seems like an issue that needs working through as can’t be pin pointed.

If it was a leak why would turning the engine on and off sort it, surely it would be consistent?

At a loss of what to do and wonder if anyone had an experiences or advice?!

Thanks in advance

[E-bmw]

Petrol or diesel?

Engine size?

Age?

Car history?

Just for starters.

[GreenV8S]

Could be a combination of a sticking stepper motor on the idle control / throttle actuator, and/or the engine being slightly out of tune and not responding to idle controls as expected. A good cleanup of the idle/throttle mechanisms followed by a service would be a good start.

[GRIFFLG]

Thanks, is petrol, 1.8 litre, 2006 approx 134k on the clock always had regular servicing.

I can see it just being quite expensive in whittling down what it could be and ideally want to sell it as has mot until jan next year but don’t want to spend much more on it!

[GRIFFLG]

The accelerator does sometimes feel a bit ‘sticky’ come to mention it

[dave_s13]

Try unplugging the maf or map sensor, depending on which it has, and see if the idle improves.

Some air leaks will show up by spraying carb cleaner around any of the vaccum lines.

[GRIFFLG]

Thanks, if there was an air leak could it sort itself out but me just turning the engine on and off? This is what is confusing me it somehow resets itself and is fine again for an hour or so..

[PositronicRay]

A sticking purge valve can be intermittent. Easy to check check too.

[Blanco92]

I’ve never spannered a Mondeo, but an equivalent era Beetle I had once was giving similar symptoms... intermittent “hunting”

Problem eventually turned out to be the power steering pressure switch. To be fair, the diagnostic had flagged this intermittently before. It just wasn’t obvious to me that the two things were linked! Might be worth a look if Mondeo uses a similar design.

[lyonspride]

I think may find that the behaviour changes/improves when you actually come to a stop, the Mondeo is "fly by wire", you don't have direct control over the throttle and the car does all sorts of "helpful" things, like holding the revs when your changing gear, the most annoying symptom is when you dip the clutch and try to rev the engine, there is a short delay where you can't do that, then beyond that delay with the clutch still dipped the engine revs freely without issue.

So as you see the car is monitoring the clutch, the gear position and the road wheel speed, and is then messing with the throttle depending on those inputs. Basically this means that something that should be unrelated might actually cause your problem.

I actually get a similar issue to yours, but it stops as soon as the car comes to a halt.

[GRIFFLG]

If I stop and disengage the clutch it still continues, I’ve replaced the purge valve and still getting the same issue, so frustrating.