Erratic idle Range Rover

That sounds a bit strange - I've set a few on the earlier Vitesse setup, and never had to do this. Were you using a high impedance DVM?

IIRC, this only opens on the over-run at high vacuum - its purpose is to reduce hydrocarbon output under those conditions by admitting air. It certainly shouldn't open at tickover.

Again, that's not an idle adjustment - it's set to give a small clearance to the butterfly, and shouldn't be played with after it's been set. For the Vitesse, the figure is not exceeeding 0.1 mm (0.004 in)

I'm not familiar with this version of the EFI, but presumably it uses a stepper motor to set the idle speed? And since at idle it's running open loop, I'd say all the adjustments you've mentioned would be pretty critical. Once it goes closed loop, the ECU will take over and adjust accordingly.

FWIW, all the above is only a semi-informed guess. ;-)

Yup.

I think it also controls the tickover - it opens and closes to by-pass the butterfly to speed up and slow the idle.

Different allan screw! The one that sets the butterfly 'shut' position is (now) set to 2 thou clearance (as per spec). The otherone that controls the tickover speed allows air to bleed to the stepper motor part.

Well - I've just taken the plenum off and it looks like a prvious owner has had a play in there - 3 of the trumpets are missing (which can't help) - so I've replaced them. Stripped and cleaned all the moving parts and made sure there is no play in the throttle spindle... Now about to bung it back together (with some silicon to seal the plenum as that was also not sealed).

Surely if fitted with an 02 sensor (the OP doesnt state this, but I would think a 92 hotwire will be) it should be running closed loop all the time, when hot.

The OP's problem, as I read it, is that the A/C idle up valve is, for whatever reason causing the tickover to jump up too high and is making the ecu actuate the deceloration fuel cut off- as it can see the throttle is fully shut yet the revs are above the trigger level- usually 1200-1500rpm- its shutting the injectors off altogether- hence the bouncing idle.

Check out that idle up valve!

Tim..

Right - so it's got an in and out pipe? The earlier Vitesse setup uses one or two of these valves - one, at the front left of the engine to speed up the idle when the aircon is switched on, and the second (if fitted) at the back of the plenum to equalise the idle when you engage drive in an auto. But I assumed later vehicles with a stepper motor controlled idle did away with both these, as they are part of the purely mechanical cold idle pipework.

I suppose it has got a stepper motor to control idle? Sounds by your description it's the same as the early cars - apart from the hot wire AFM.

It's not sealed as it leaves the factory, and shouldn't need anything unless damaged.

Well if it does have an O2 sensor, it will be buggered soon anyway, the OP just said he's gonna use silicone to put things back together.. the best way to screw sensors up on an engine,

the fumes the silicone gives off while it's setting are very bad for engines, and coat the sensors or something.. look in any decent motor factors and they'll sell a sealer that stated as O2 sensor safe, locktite do one.. 510 or something like that, it's an orange kinda colour in a small tube,it'll say on the back what it's for.. i.e mainly re-assembeling engines that have O2 sensors and the like.

It doesn't have an O2 sensor - It's not got a cat - just built a few days to early to need one.

Haynes and the Land-Rover workshop manual both say that the plenum top should be sealed with silicone - I actually used Blue Hylomar because I had some and because it's easier to remove later.

I don't think so - It's a Land-Rover! All it does is (supposedly) control the idle speed depending on load.

Now checked thoroughly Sah!

It seems to be working happily - nice and clean and winding in and out happily - just too far I think, so the tickover goes too high, then it winds back too far and it slows too much.

It is better now I've had it all to bits and back together - but it's still not right.

The stepper motor controls the idle valve - it's on the back of the plenum and has a rubber hose to a stub just upstream of the throttle butterfly.

Should be sealed (according to BOL and LR w/s manual). It's now sealed with Hylomar.

AFAIR the one at the back of the plenum is the overun valve. It should be closed at tickover. The one you are refering to is what is called the extra air valve. A valve that does allow air to bypass the butterfly. On the Vitesse it is near the o/s front of the plenum

That screw. The idle adjustment screw, should give a greater difference than that, which suggests it is having less affect on the volume of air flowing than it should. That could indicate a fault with the setting of the a/f meter itself. Maybe the previous had a play with that. They are adjustable once you remove the lid. The Vitesse a/f meter has an idle air fuel mixture adjustment screw. A bypass that allows unmetered air into the plenum. Maybe tweaking that will make a difference. Mike.

I suspect that the Vitesse is different - the Rangy has only the one valve - and it definitely controls the tickover.

Yes - but I can't see how - if feeds (via a 1" rubber pipe) to the afrementioned stepper motor controled valve on the back of the plenum. I can't quite get my head round how it's going to work really. The screw allows more or less air to flow from upstream of the butterfly and into the plenum via the valve. If the valve is shut, nothing will happen at all by opening the screw? If the valve is wide open (demanding more revs) then if the screw is shut nothing will happen?

I'd say the MAF is OK as the mixture at tickover is spot on - I set it a few weeks ago to 0.7%CO and it's still at that when I rechecked it this morning.

It might - but would move the mixture outside spec!

Interesting. That's exactly where the over-run valve is on earlier versions. Do you know where they've moved it to on yours?

Not according to my SD1 manual. Perhaps they'd forgotten how to machine on later engines? Both the plenum joints were 'dry' straight from the factory on mine.

Her's a pic of it url:

That seems very low - is that the spec? The earlier engine is 1.5% CO, but most run at around 2.

The spec is 0.5 to 1.0%CO on this model.

I'm starting to think it could be air-flow sensor or ECU related :-(

Nope - Although the SD1 had the earlier type of EFI - on that there was a second valve (just been looking through the Haynes) that connected into the plenum on the opposite side to the throttle body.

I suspect that they were using the same tools and hadn't reground them from the day they were new! Hence the need for some sealant by the time they were making the 1992 models!

My thaughts are on the lines of 2 wrongs might make a right at a particular setting. Like if the MAF setting 'had' been fiddled with, it might be possible to adjust the CO to the correct idle setting, but it could still be mismatched to the TPS or EMU. Just a thaught that could be complete cobblers. :-) Mike.

A little job for tomorrow I reckonb :-)

I called it a day on the engine earlier - without the air-con on it runs perfectly. It's a right bugger.

Now to see why the heater blows hot all the time...