TD4 Revs on it's own

Hi guys, I have this problem for almost 2 years now and it's making me crazy.

Car basically revs up to about 2000 rpm on it's own and settles down when slowing down to about 20mph and under.

Things I concluded so far:

- it NEVER happens on cold engine, it needs perhaps 5 miles driven or so to start, it starts always after that, and basically stays the same no matter how much the car is driven.

- if I drive it very sluggishly under ~2200 rpm it kinda keeps it under control, if I "step on it" a bit - it emerges a lot faster.

- it will NEVER rev while the car is standing still, the second car slows down to ~20mph revs settle down to normal.

- it is definitely related to vehicle speed in terms of settling down, it needs for the car to slow down in order for the revs to settle down.
For example: I drive down the hill and if I press the clutch (and go neutral on manual gearbox) revs will go up to about 2000 rpm and stay there until I slow down to about 20 mph and revs will start settling down. Now when I let the car accelerate down the hill (gearbox still in neutral) the revs will also start climbing.

Every time I drive it to a garage for some maintenance I moan about this and guys at the shop checked everything inside out several times - no luck. Diagnostics shows nothing and car generally has no other problems. It runs great, very good MPG.
I do all the services on time with quality parts and generally take good care of it.
If anyone has any ideas - all suggestions are welcome

Throttle Position Sensor? If you have a decent diagnostics device that captures real time data it may show what position the ECU thinks the throttle is in.

Valid point. I will ask the guys at the shop have they checked what happens while driving it. Although can't see how reducing vehicle speed would influence TPS readings.

I've seen this several times on petrol engines, attributed to the idle control valve. However the TD4 doesn't have one so it isn't that.
I'm thinking that it could be a corrupted fuel map or something equally strange.

Quite possibly... Well my final plan of attack is to find used parts dealer and ask him to loan me TPS, MAF and ECU and hope it goes away. IF it does it's just a matter of finding which one of those is to blame. Of course it could be some of the other sensors and bits but these are the ones I doubt the most.

You can get "loan" parts from a breakers?

I was thinking of paying for them before the test, then just keep the part I need and return the rest. I just need a couple of minutes to drive around the block to see if it makes any difference or not. Not much of a plan really, I will try to go back to the shop but if they can't find the problem (again) I really don't see any other options.

wondering if it has something to do with the ABS system
i think the vehicle takes it speed reading from the abs sensors on the wheels ..

i know when mine starts to move .. the idle rpm jump to about 850 rpm
i.e. manual gearbox in 'neutral' .. vehicle rolling downhill ..
( 'home' parking spot is on a incline .. 50 yards to a level sharp turn ..
( i normally let it roll down in neutral to the turn ..
normal engine idle with vehicle not moving is about 750 rpm aprox.

so must be a connection between the abs system .. and engine ecu for the rpm rise

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adding some info re: the go-pedal .. brake and clutch switches ..

note last sentence regarding the clutch switch
although don't know if your engine symptom is 'surging' ..

( see attached pics )







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hd3 said:

wondering if it has something to do with the ABS system
i think the vehicle takes it speed reading from the abs sensors on the wheels ..

i know when mine starts to move .. the idle rpm jump to about 850 rpm
i.e. manual gearbox in 'neutral' .. vehicle rolling downhill ..
( 'home' parking spot is on a incline .. 50 yards to a level sharp turn ..
( i normally let it roll down in neutral to the turn ..
normal engine idle with vehicle not moving is about 750 rpm aprox.

so must be a connection between the abs system .. and engine ecu for the rpm rise

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Click to expand...

My first thought on this is that you must have been on the whacky backy @hd3

However, the ABS/TC is active and the solenoids (or what ever it uses to pulse/release brakes) would presumably take a fair bit of power to activate - so I could see and argument for the ECM raising revs to ensure sufficient electrical power is generated - in the same way revs are increased when AC is turned on or Drive engaged for an auto - for differing reasons.

hd3 said:

adding some info re: the go-pedal .. brake and clutch switches ..

note last sentence regarding the clutch switch
although don't know if your engine symptom is 'surging' ..

( see attached pics )

Click to expand...

My take on that surging is just due to gear changes and the ECM tries to make them a bit smoother than flooring the clutch and yanking the gear leaver - ie it thinks it can drive better than the pilot!

AlexTD4 said:

Hi guys, I have this problem for almost 2 years now and it's making me crazy.

Car basically revs up to about 2000 rpm on it's own and settles down when slowing down to about 20mph and under.
Things I concluded so far:
- it NEVER happens on cold engine, it needs perhaps 5 miles driven or so to start, it starts always after that, and basically stays the same no matter how much the car is driven.

- if I drive it very sluggishly under ~2200 rpm it kinda keeps it under control, if I "step on it" a bit - it emerges a lot faster
- it will NEVER rev while the car is standing still, the second car slows down to ~20mph revs settle down to normal.

- it is definitely related to vehicle speed in terms of settling down, it needs for the car to slow down in order for the revs to settle down.
For example: I drive down the hill and if I press the clutch (and go neutral on manual gearbox) revs will go up to about 2000 rpm and stay there until I slow down to about 20 mph and revs will start settling down. Now when I let the car accelerate down the hill (gearbox still in neutral) the revs will also start climbing.

Every time I drive it to a garage for some maintenance I moan about this and guys at the shop checked everything inside out several times - no luck. Diagnostics shows nothing and car generally has no other problems. It runs great, very good MPG.
I do all the services on time with quality parts and generally take good care of it.
If anyone has any ideas - all suggestions are welcome

Click to expand...

I'm going to say summat that has NOTHING to do with Land Rovers, but bear with me please ...

On our Nissan Note, I noticed the same thing, mainly when driving at 20mph in third gear ... if you take your foot off the throttle to let the engine slow slightly ... getting to a speed table ...
It would accelerate noticeably, when I mentioned it to a Nissan mechanic he said it was probably the anti-stall kicking in ...
Maybe you have a similar thing, whether it's working properly or not I can't say ...

It could potentially be something to do with the ABS ECU. These have been known to cause all sorts of odd faults.

My first thought on this is that you must have been on the whacky backy @hd3

Click to expand...

fair do ;-) .. but haven't partaken for the past 10 years or so ..

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on a side note .. 'n totally off-topic .. and because it were snowing today near Blubberhouses ..
how's this for some fun ..
http://www.topgear.com/car-news/video/watch-tracked-jeeps-have-fun-snow
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They look like great things to play with - but only if you've got very deep pockets! There must be some heavy duty engineering in them.

Thanks for all your help guys!

I booked diagnostics mid next week, I will drive around first to get the problem to appear then I'll drive around with diagnostics attached to check all values live.

I found the clutch switch, it doesn't have any mechanical moving parts on it so it must work using magnetism or something. It has 4 pin connector going out, anyone happen to have pin test values so I can test it out before I go to the shop?

Also found brake switch, which is ordinary sliding switch. It has 3 pins where (probably) 1 pin is current in, 1 is for back lights and 1 for ECU. Checked with multimeter, all seems good.