Brown Trouser Moment!

Range Rover P38 MkII, 4.6 HSE, automatic.

Hello, new to the forum, so be gentle with me please

After jumping it to start (seem to get a flat battery every few days - must see what's taking the juice, I have seen many threads, so as I don't use the alarm I'll just disconnect the receiver!), it revved to 6000rpm (not touching the accelerator) then settled back to a fast idle.

I let it warm up then drove off, I accelerated to join the traffic but when I took my foot off the accelerator, nothing happened and I carried on accelerating. Applying the brakes hard and turning off the engine meant I stopped! [buttock clenching moment!]

On restart it was fine, but I always have had a delay on releasing the pedal to the revs dying away (cruise control is off).

When the cruise control is on and is use, it seems to work fine.

The throttle cable is fine and moves freely, as does the business end at the engine.

Could this be the cruise control getting involved when it shouldn't? I am thinking about just disconnecting the cruise control linkage and seeing if that is the culprit?

Cheers

Peter

Check your air intake hose for splits that could be opening and closing as you drive. Battery drain can be tricky to tie down. How long have you had the car, has it always done it or just recently? If it's just recent behaviour it could just need a new battery - these things need good voltage especially this time of year. The racing engine could be overfuelling due to an electrical problem. If the basics don't turn anything up best to get it plugged in to a testbook or something to check for stored faults. Oh and instead of hoofing the brakes on and switching off (which loses steering control - worse if it locks) just slip it into neutral. Not very good for it but at least stops you driving over the car in front.

Blenheim Rover said:

Check your air intake hose for splits that could be opening and closing as you drive. Battery drain can be tricky to tie down. How long have you had the car, has it always done it or just recently? If it's just recent behaviour it could just need a new battery - these things need good voltage especially this time of year. The racing engine could be overfuelling due to an electrical problem. If the basics don't turn anything up best to get it plugged in to a testbook or something to check for stored faults. Oh and instead of hoofing the brakes on and switching off (which loses steering control - worse if it locks) just slip it into neutral. Not very good for it but at least stops you driving over the car in front.

Click to expand...

Sliping into neutral whilst the engine is uncontrolled accelerating for a unknown reason will cause the engine the red line possibly damaging god knows what!
The best thing to do is get it under control as soon as possible, and if that means shuting it down then so be it!

gfromleeds said:

Sliping into neutral whilst the engine is uncontrolled accelerating for a unknown reason will cause the engine the red line possibly damaging god knows what!
The best thing to do is get it under control as soon as possible, and if that means shuting it down then so be it!

Click to expand...

See the last sentence of my post.

You will also have read the initial post where it says it has gone into free rev mode. Being a petrol engine there will be a rev limiter too so it wont do an uncontrolled diesel death. The reason I advised not to switch off is that in a panic situation it could be easy to pull the key out and lock the steering. All said and done best not to drive it until fixed.

An update.

It is a GEMS engine. I have removed the linkage from the cruise Control and the fault persists.

I am therefore down to it probably being the throttle cable. It looks easy enough to remove, so prior to a replacement (which is probably the best option) I will remove it, check for free play then oil it - there are a couple of tight curves in the routing that over a period of time, may give rise to issues.

Peter

More info. Flat battery again today

Jumped it, didn't touch the pedal, but it raced away again. I have established it isn't the throttle cable and it isn't the cruise control linkage.

But, when I went around to the throttle linkage to reduce the revs it was hard round and there was a definite stiff point that I had to move it past before it sprung back. Then it was OK again, you could rev the engine and it would return to idle naturally.

So, what is in the plenum chamber and how is the throttle linkage and the stepper motor linked? I know I've been told that the stepper motor should be able to race the engine, but it almost seems that it interferes with the free movement of the throttle (and prevents it returning). But I have no pictures of what is in there!

Cheers

Peter

if this fault comes and goes and all is well sometimes, it could be the throttle position sensor...
I have the same fault and am awaiting a new - second hand sensor to appear.
my 4.0l only idles at max 3000rpm when its playing up, and the stored throttle position voltage at the ECU fluctuates all over the place when it should be a stored number, ecu then makes engine run at variable rpms, draining my fuel tank in the process.
that's what is wrong with mine...... the way I see it.... clear as mud.