Revs Sticking

[barnowl005095]

hi, it's been happening a lot in the last couple of weeks. when the car has warmed up , i pull up to a junction, dip the clutch, if i touch the accelerator the revs go to about 1500 and stay there. Even out of gear. i have to put in gear and move clutch to bite to lose the revs.

any help would be appreciated

thanks

Focus 2008 TDCI 1.8 Estate

[artscot79]

sounds like the clutch may be slipping

[Tdci-Peter]

13 hours ago, barnowl005095 said:

if i touch the accelerator the revs go to about 1500 and stay there. Even out of gear.

I suspect it has to be the throttle pedal sensor. In a TDCI, Engine rpm is sensed & controlled by the PCM. It just alters the amount of fuel to the injectors. Injector or PCM or crankshaft sensors would surely have other, more obvious symptoms, when driving.

The pedal sensor will wear most right at the bottom end, so that is where is most likely to fail.

The pedal sensor is a dual (redundant) pair of pots, one goes to the IC, and one direct to the PCM. These readings should be compared and a warning light come on if there is a bad error (pedal sensor is a safety critical part). But very small errors at the bottom end may be undetectable.

Probably needs a new sensor. That is my best guess on the info provided.

Peter.

[mjt]

On 23/06/2016 at 8:40 AM, barnowl005095 said:

I have to put in gear and move clutch to bite to lose the revs.

Do the revs stay 'lost' once you've done this? If so I wouldn't have thought it could be a throttle position sensor (TPS) issue. I can't think what might do that though, so you may have to get it diagnosed by a Ford stealer.

[barnowl005095]

I know the clutch is going as it shakes the car when idle. think it might be the bearing going. Once it starts doing it it doesn't stop. i can rev again and it will hold then de clutch to kill it and then do it again. a few people have suggested it may be the throttle body that needs cleaning or the auto choke. can these be ruled out?

[mjt]

They can be ruled out. The 1.8TDCi doesn't have a throttle body or auto choke, the engine is controlled solely by the amount of fuel injected.

If the clutch shakes the car at idle it's probably the DMF on the way out.

[Tdci-Peter]

On 23/06/2016 at 8:40 AM, barnowl005095 said:

Focus 2008 TDCI 1.8 Estate

As Mike says, Diesels have no throttle or choke.

If the DMF is going, and making the car shake, then it is just possible this is confusing the PCM (which gets its engine speed measurements from the flywheel), and it is unable to maintain the normal, 850rpm. You probably need to get the clutch fixed first, in that case.

I still suspect a fault with the pedal sensor, though. Does the high idle only happen when the car is shaking?

It looks like you said the high idle does repeat each time you dip the clutch (ie. revs drop when the clutch is moved to bite, then rise again when clutch is dipped, without touching the accelerator pedal), though it is not 100% clear.

Peter.

[mjt]

I agree, Peter. I interpreted it as the revs staying low after the clutch has been used to bring them down, until the throttle is blipped again, but Matt's wording is a little ambiguous.

[barnowl005095]

hi ref Peter, It only shakes say when parked up in neutral (I get a loud clattering from the engine). regs revs, its only when I touch the accelerator it revs but it stays reved. I then have to put into gear and declutch for it to go away, but it stays gone until I touch accelerator again. it's like its not releasing something and then the clutch being let out uses the revs and brings it down again.

Thanks

[Tdci-Peter]

5 hours ago, barnowl005095 said:

It only shakes say when parked up in neutral (I get a loud clattering from the engine). regs revs, its only when I touch the accelerator it revs but it stays reved. I then have to put into gear and declutch for it to go away, but it stays gone until I touch accelerator again.

Shaking and loud clattering at idle sounds suspiciously like DMF. Got a snake Cam? If the starter motor is removed, it might be possible to get a view of it, and test it by either rotating the engine (bolt on crankshaft pulley?) with the transmission locked, or rotating a road wheel the the flywheel locked. Sometimes, iron filings can be seen with the starter removed, from a failed DMF. Probably a garage or clutch specialist job really.

As for the idle speed fault, that is a mystery. There are no mechanical linkages in the engine bay, it is all electronic. The pcm reads pedal position & rpm (from crank sensor), and adjusts the amount of fuel injected. The only thing I can think of is the throttle pedal is mechanically sticking open a little, and using the clutch pedal (deflecting the pedal mounting area a bit) frees it. Or, just possibly, the DMF fault may be making the pcm raise the idle.

Peter.

[mjt]

Again, I have to agree. The sound you describe is almost certainly coming from the DMF.

Interesting comment Peter makes about the possibility of a sticky throttle pedal. Have you tried hooking your toe behind it to see if that brings the revs back down?