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[Simon72]

Right got a problem with a 3.9i Land Rover Discovery Manual, fuel injected.
Its my mates Disco and we use it for Off-roading and Charity events.

Here's the problems that started with..

1 Struggles to start but starts eventually
2 Erratic tick over - between 900-1200 revs
3 Flat spot around 2200 revs

Things done so far...
After numerous websites and forums later decided that the idle issue was down to the 'Idle control valve, £60 later - no difference   
Bit the bullet and took it to a garage - Mass Airflow Meter the problem! plus a couple of other bits changed, £292 later and it is still exactly the same, apart from running a lot smoother without any flat spots!

So he has spent £352, it still doesn't like starting and after 'load' it idle's at 1500, drops to 1200 then settles eventually at 850ish.
Any suggestions would be much appreciated as he is fast reaching the point of nice Mr Scrapman!

Also new battery changed.

Symptoms now....
Cranks and cranks and cranks and eventually fires up (usually flattens battery so now running with dual battery)
Flat spot has GONE 
But revs don't settle immediately after a drive and stopping at junctions (usually at 1250rpm ish)
Then after 20 seconds drops down to 850ish.
You may think this bit with the revs are not a real problem, BUT when in low range off-road it does cause a few problems when you don't want it doing what it wants 

Any suggestions welcome, or any Rover V8 experts in the Wolverhampton area 

[Arrolman]

Hi Simon,

Have you posted on landrovernet.com, usually an expert or ten on there, if you do a search in the discovery and range rover forums im sure you'll find a few posts

Cheers,
Iain

[Andy H]

I have rebuilt a couple of 3.5 V8s (with carburettors) nothing as modern as the 3.9.....

Does it have a distributor? Is the advance mechanism moving freely?

[Simon72]

I have rebuilt a couple of 3.5 V8s (with carburettors) nothing as modern as the 3.9.....

Does it have a distributor? Is the advance mechanism moving freely?

Yes.
The advance and retard was jammed, the vacuum unit has been replaced. Car has been tuned and timing spot on the marks.
Posted on several land rover forums, same answers as what we have already checked and changed.

[cem_devecioglu]

starting issue engine hot or cold ?

[Simon72]

Starting you have to bury foot on floor while cranking, and it will start.

Revving idle is always when hot and after you have been driving for a while and it is hot.
Idle stay high for approx 15-30 seconds and then steps down to correct idle.

Also just remembered temp sensor / plugs and all leads and HT lead have been changed.
Vacuum pipes all checked and clear and no leaks.

[Andy H]

Early carburettor RRs had little spring loaded valves on the throttle butterflies for emission control .

When the springs got weak they would stick open and give a fast idle just when you didn't want it. The cure used to be to solder them shut.

Rover wouldn't have done the same on the 3.9 would they 

[cem_devecioglu]

Starting you have to bury foot on floor while cranking, and it will start.

Revving idle is always when hot and after you have been driving for a while and it is hot.
Idle stay high for approx 15-30 seconds and then steps down to correct idle.

Also just remembered temp sensor / plugs and all leads and HT lead have been changed.
Vacuum pipes all checked and clear and no leaks.

on some cars it stops the injectors..not sure for RR though.. must say, hot and cold engine start isues are caused by different things, but if it does in both conditions .....

[RobseyMV6]

Hi had a p38 V8 4.6 range rover with bad bad starting and running  turned out to be the crank sensor was hitting the fly wheel pick up as the pot rivits come lose and started touching the sensor.... changed my fly wheel but you can just put some washer under crank sensor to make a gap? 

[2woody]

this still sounds like an idle regulator problem to me....

On the Rover, this is a stepper motor device, which remembers where it is when turned off. If you have the idle stop screw backed too far off, you're leaving the regulator a lot to do - it's got to move a long way to maintain the idle.

disconnect the regulator and get an idle at just under the 850 revs using the screw. Then reconnect the regulator and wait for it to stabilise. BUT beware that if you've got an idle above the 850, the regulator wil never do anything.

also beware that if the ecu power is ever switched off, the idle will have to re-learn.

Also, check the vacuum signal to the ecu, this is the most important signal it receives.

Just for reference, the Rover control system holds the idle speed above idle at road ends, etc. until the car has firmly come to rest.

[Marks DTM Calib]

First question has to be ....what year.

As the subtleties of the EFi setup changed on the 3.9 from when it was first introduced (1989).

[Nick W]

Rovers are very good at hiding knackered cams, and when they get really bad cause all sorts of rough running.
It's always worth pulling the rocker covers, and seeing what happens when it's running. It's quite common  to find the valves for the back two cylinders aren't opening much, if at all.

[Simon72]

First question has to be ....what year.

As the subtleties of the EFi setup changed on the 3.9 from when it was first introduced (1989).

It's a 1994 N-reg, if that helps.

Brilliant advice so far. Will check a few things that have been give.

[sassanach]

and does it use a sh*t load of petrol?(more than normal lol)

[Simon72]

and does it use a sh*t load of petrol?(more than normal lol)

It's a V8, lol about 12-18 mpg 

No more than normal