Need help with my 3.9L

[DEF110]

I have a 3.9L with a ZF auto box in my 110. the 3.9 runs well but when it gets to operating temp and have driven 20 miles or so it will not idle when I come to a stop.
As soon as I come to a stop and do not have my foot on the throttle it will stall. It starts back up and if I keep my foot off the throttle it will die again. I have cleaned the butterfly area in the plenum. Also when I changed the valve cover seals I had to take the plenum off and I cleaned all the gunk that was built up inside.
I am thinking it is a fuel air mix problem but not sure. It has an K&N air filter on it, could this be the problem as it is now getting to much air flow at idle?   :?:  :?:

[Thrasher]

This sounds like it could be the stepper motor on the plenum chamber. You need to unscrew it and clean it. I have a spare somewhere if yours has passed it's sell by date :-)

It's on the drivers side, near the back. There is a connector going into it - you can't miss it :-)

[Henry Webster]

I have had a similar issue in the rally car, but I'm not entirely sure what I did to correct it.

First off I would check for air leaks - if it is ingesting air from somwhere it shouldn't it might have this effect.

Secondly check that the extra air valve (back of plenum chamber) is working satisfactorily it contains a stepper motor - maybe take it out and give it a bit of a clean.

The official Land Rover 'testbook' does a test cycle for the extra air valve, but I'm not sure off the top of my head how to do a DIY test.  Have a look at the Haynes manual.  You can also tweak the base idle, but if the extra air valve is slow or misbehaving this will not sort the problem.

If none of this works, you'll just have to wait for someone more knowledgeable than myself to turn up...

[Henry Webster]

This sounds like it could be the stepper motor on the plenum chamber. You need to unscrew it and clean it. I have a spare somewhere if yours has passed it's sell by date :-)

It's on the drivers side, near the back. There is a connector going into it - you can't miss it :-)

Beaten me to it - serves me right for being so verbose! :lol:

[Henry Webster]

I have had a similar issue in the rally car, but I'm not entirely sure what I did to correct it.

First off I would check for air leaks - if it is ingesting air from somwhere it shouldn't it might have this effect.

Secondly check that the extra air valve (back of plenum chamber) is working satisfactorily it contains a stepper motor - maybe take it out and give it a bit of a clean.

The official Land Rover 'testbook' does a test cycle for the extra air valve, but I'm not sure off the top of my head how to do a DIY test.  Have a look at the Haynes manual.  You can also tweak the base idle, but if the extra air valve is slow or misbehaving this will not sort the problem.

If none of this works, you'll just have to wait for someone more knowledgeable than myself to turn up...

[DEF110]

Thanks I will take a look at it tomorrow.  :)  :)

[Range Rover Blues]

The oil breather system also allows air to the plenum at idle, the butterfly cuts air off completely.

[DEF110]

I cleaned the stepper motor and it is still doing it.  No air leaks, I took a can of starting fluid and sprayed all around the plenum with the engine running and the idle did not change at all.
Is there a way to bench check the stepper motor?

I just may need to junk the EFI system and go with the Edelbrock intake and carburetor. I can get them out of the U.S. for about $500 (£275) and I am going to the U.S. mid December.
Dose anyone know if the 3.5L intake is the same as a 3.9L? I contacted Edelbrock and they said they only make one for the 3.5L. For what I know the engine is the same just a bigger bore and the valves are larger. The basic engine is the 215 Buick. So any advise would help.

[Range Rover Blues]

If I leave ours with the ignition on and the engine not running you hear the stepper motor cycle through it's range every few minutes.