Idle Problem

**westonben** · 27th July 2008, 05:24 PM

Hi, I'm having some problems with my Series 1 Disco. It's a gulf spec 1999 3.9i without Cat. It's covered 104k kms.

Symptoms: When the engine is hot, pulling up at lights etc. the revs can dip. However, when stationary the idle also bounces up and down a little. It sits steady at about 700rpm for a while before dropping bit at a time down to 500rpm (engine sounds like it's stalling/labouring) a little click can be heard and the revs jump back up to 700rpm. Cycle repeats until I'm rolling again. No other issues with running.

What is ruled out:

MAF (tried known working ones)
TPS (tried known working ones)
AICV/Stepper (replaced) Mating surfaces spottlessly cleaned.
Checked leaks on all pipework
Fuel Pump (new)
Fuel Filter (new)
Leads/Plugs/Rotor Arm/Dizzy Cap (new)
Coolant Temp Sensor (new)
Throttle body (cleaned spotlessly)
Crankcase Inlet Air Filter (cleaned)

What's left:
Fuel Pressure Regulator
Fuel temperature sensor
Blocked injectors (tried cleaners)
Head Gasket
VSS
ECU
Slit Wrists?

Where do I go from here? The dealer has not been able to diagnose the problem and the other garages here (qatar) are very crude.

Appreciate any help as it's getting well beyond a joke now!

Thanks

Ben

**Utemad** · 27th July 2008, 05:35 PM

The Idle Air Control valve at the back of the plenum chamber.

Pull it out and clean up the plunger and its mating surface.
Maybe need to replace it?

Mine used to do what you describe but not quite as bad. Usually only when it was cold.

**INter674** · 27th July 2008, 05:48 PM

. that sounds normal to me - ours has always done that. Young relative actually asked me why does it do that...to which I replied...it's a Land Rover, that's why....and he nodded sagely...

**Utemad** · 27th July 2008, 05:57 PM

Just saw the IAC valve is on your list of done things.

If you unplug it does the problem stop or at least change?

**westonben** · 27th July 2008, 06:10 PM

It might normal to fluctuate a bit, but it's also occasionally stalling. That can't be normal?

WRT to pulling the stepper, do I do this while the engine is running????

mike 90 RR · 27th July 2008, 06:18 PM

If you have no catalic converter // then you did a exhaust change?? .. Did you keep or are you running the Oxy sensors??

**Utemad** · 27th July 2008, 06:21 PM

Originally Posted by westonben

WRT to pulling the stepper, do I do this while the engine is running????

I just meant unplug it.

When the engine is running unplug it and see if the idle stays the same or continues to fluctuate.

**mickashay** · 27th July 2008, 06:29 PM

mine is doing this also,when i pull up the revs bounce up and down then are ok when driving,was out in some very slippery hills today and it was doing it real bad when coming down the hills and stalling alot,i have cleaned the idle air control but still didnt change any thing???what else should i look at also

**harry** · 27th July 2008, 06:31 PM

Originally Posted by mike 90 RR

If you have no catalic converter // then you did a exhaust change?? .. Did you keep or are you running the Oxy sensors??

i run a 95 aussie disco, factory no o2 sensors or cats, so i guess his is also standard there.
you mention the stepper motor has been cleaned, has it also been lubed in its own shaft?
i also have endured this hunting at the lights and stalling , one fix was the replacement of the engine temp probe, and this problem still persists with mine now and again.
sometimes it is as simple as turning the ign off, waiting briefly and re starting the engine
i really believe the problem is directly related to the temp sensor.
however someone may be able to give you more clues - good hunting [no pun intended]

**duncanw** · 27th July 2008, 07:53 PM

the exact same thing happened to mine, I cleaned out the stepper motor with no change so I bought a new one and it fixed the problem.

Regarding whats remaining on the list of possibles, I doubt very much its the fuel pressure regulator, mine also died and it was crap across the whole rev range, could only manage 80km top speed and it stank of petrol.

Blocked injectors ? your fuel economy would be crap and it would be lacking power on the whole range, pull your plugs out and have a look at them, if their black it's not usally a good sign

Head Gasket, doubtful, again it would be crap across the whole range, do a compression test and see if its in the normal range.

Maybe if you check your vacuum lines ?

Do you hold the brakes at the lights when the engine wants to die ? I had a faulty brake booster and if I put the brakes on at idle it would drop the revs.

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