I recently removed, disassembled and cleaned my intake manifold on my 1999 LRD1 GEMS 4.0L. Now I have BLACK soot completly saturating my spark plugs and blowing out the tailpipe. I'm sure it is a lean/rich problem. I have tinkered with the choke valve and idle air control valve, but do not know the exact specs to get the LRD1 back to normel. Any suggestions?

 

What do you mean by "tinkered" and what "choke" valve? What did you do to the IACV? it is not adjustable... so please clarify.


Are you sure of your model Disco? series 1 or 2? I ask because you changed your profile name to say LRD2 yet you are saying it is a D1....

 

Yes I do have a D1. The choke valve I'm talking about is the throttle body valve. The IACV is adjustable. It can be screwed in and out in small increments. I have tinkered with the IACV by measuring the distance from the the gasket to the IACV contact point inside the throttle body. Also by opening and closing the allen screw located to the top of the IACV assembly. The throttle valve has been removed, clean and reinstalled. However the angle of the throttle valve or choke valve placement is not known. I was told it is supposed to be straight up and down, which would be in the fully closed or choked position.

 

well then....

The butterfly valve in the throttle body is to be closed (up and down as you put it) when you are giving it no throttle command. If air is allowed to get past the valve then the IACV will attempt to close in order to maintain an ilde rpm of 700 based on "closed" position of the TPS and if the VSS simultaneously senses no vehicle movement.

The ECM will adjust the IACV based on signals from various sensors (MAF, RPM, O2's, TPS...) and vehicle speed (VSS). any adjustments you make to the valve will be setting the valve outside of it's parameter range. If you screw or unscrew it the ECM will override your adjustments and supply the engine intake with the appropriate amount of metered air. UNLESS you have "adjusted" it to an extent where command input from the ECM is unable to compensate for the new conditions. Simply make sure it is clean (both cone and mating surface) and that it has a good solid gasket then screw it in and make sure the plug is connected correctly. The ECM does the rest.

How long have you been a Rover owner?

 

I know my throttle valve is still out of place. I will make sure it is positioned correctly. I was sure of most of what you said, however it is very difficult to reassemble everything exactly the way one finds it. In my instance I definitly did not set the throttle valve right. Well this is my second rover. My first was a 97 D1 that went up in flames. I purchased it while I was on R&R from Afghanistan. When I came home I drove it for about four months until the battery positive cable shorted to the frame causing the transmission wire harness to flame out. I salvaged everything except the body, diffs and wheels. Figured I had alot of parts now, so I went out and bought a 1999.

 

I had the same problem with soot when my intake manifold gasket was leaking.

Cosmic: I believe the choke screw he is talking about is the screw that is supposed to be under a protective cap right above the IACV. RAVE says it is set at factory and should not be messed with unless using a testbook or similar to measure changes.

 

I believe he thinks he "adjusted" something. methinks he messed something up attempting to adjust something he should not have messed with.

 

Certainly if it was set at the factory,"like everything is " when NEW, then there is a setting that can be followed. Sooo where is this information. I have read about turning the IACV screw to establish the correct RPM's. The only set of information I found in Rave, that could be used is the recommended vehicle RPM range. Which requires turning the IACV screw and setting the RPM's to the correct range.

 

If you go out and buy Testbook, you can set it correctly.

 

The screw you are (hopefully not) adjusting is the base idle adjustment screw. This is called a base idle screw because it is simply the initial and primary adjustment for idle... when and if there were no Idle Air Control Valve, no throttle valve bypass circuit and no electrical or mechanical loads on the engine at idle.

It is a bad idea to set the base idle screw just for the sake of recalibrating your idle. It is a GOOD practice to adjust the idle screw if you replace the plenum chamber cover / throttle body. Since you removed it and replaced it with what I presume is the original after just cleaning it then the idle screw didn't need to be reset. BUT since you did it is pretty easy to fix this.

Remove the IACV by disconnecting its electrical plug and unscrewing its two mounting screws. Since we had a bit of a miscommunication about what is an IACV and what is a Idle adjustment screw and since you said it has all been cleaned I'll assume that the IACV has been removed and cleaned. Either way let us know and we'll walk you through that seperately.

You now want to plug up the hole you just made. Find a bolt, a piece of hose which will barely fit over the bolt, and its nut with two washers. Make that into a screw plug. (again if you would like help on that just ask). that is to be used as your IACV port plug. Tape over the hole is just ghetto and could let in a bit of air which will throw off your idle screw adjustment off.

Start the engine with all Idle air ports closed off and no loads on the engine (compressor, or anything electrical like fans, lights, etc...). You need to adjust the idle screw only when the eigine is warm at operating temp.

With a warm engine running only on intake air when the throttle plate is in its closed position then you adjust the idle screw so that you get a lower than normal idle...around 525 rpm. It would be best to set the rpm with an independent tach but the one in the dash will do. If the idle hunts and can't hold steady in order to set the screw then you have other issues like MAF, O2's, Injectors or spark that need to be corrected first. The only way to set the idle is if the engine runs smoothly at idle.

If you can get the idle set and steady at 525ish then you are have just set you base idle... congrats. Turn it off.

Remove the port plugs and now make sure all that junk works and is put back together right. start it up and your iacv should work to maintain idle around 700 rpm with no input from the throttle. Also check for leaks around the intake hose joints and the plenum base with carb spray.

Just become very familiar with chapter 19, SFI section of the Fuel INjection pages of the Rave. Good luck