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High revs on starting V8i ?

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At times when starting from cold the engine "ticks over " at over 2000 rpm. :blink:

I have cleaned and lubricated throttle cable etc etc and this has made no difference.

If i turn the engine off and restart once or twice it then seems all ok with fast idle at approx 1000 - 1500 rpm ?

Any ideas of where to look/check ? Thanks.

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All PI V8's start up with high revs but then soon drop back within 5 seconds or so to around 1000rpm the as the engine warms the revs drop down to tick-over all in about 25/30 seconds, all that is controlled by the engine ecu so you may have a prob with the ecu temp sensor, how does the engine run when it's hot and what else have you done under your "etc etc" bit, have you removed cleaned the stepper motor?

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The etc etc definitely does not include a "sticky stepper" ! I have no idea as to what this is where it is or what it does ! Is there a way of testing or is it just by replacing with a new unit ?

Any info would be much appreciated.

One other thing i did carry out was to clean up the throttle body which was bogging.

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Stepper = idle air control valve,yes ?

Is it worth cleaning and checking or preferable to replace with new ?

Is it situated on the rear of Plenum Chamber ?

Thanks for your help so far.

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Ok i'll give it a good clean up although i have seen somewhere on this Forum that cleaning is possibly only a temporary fix ?

What would be best to clean with ?

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Horrifyingly expensive ?

Looking on flea-bay at item no. 370308360463 it doesn't appear too expensive although uncertain as to the quality !

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The stepper is indeed on the back of the plenum, with a waterproof four pin plug. It has a large hex-head but only requires a little torque so be careful when putting it back in. It has a fibre (or similar) washer. I will call it 'the bypass valve' or 'the unit' from now on.

The problem is that when you turn off the engine the ECU withdraws the plunger in the bypass valve ready for the next start, so that if you remove it and clean it you are not really getting to the bit of the shaft that is gungy. I have cleaned mine many times in this condition with only temporary effect. The way I got a more long lasting effect was to think a bit laterally: I decided that I needed to get at it when it was fully 'out' and so I did the following:

1. Cleaned it in the withdrawn (normal) condition as best as I could with brake cleaner.

2. Put a 2nd washer on the fitting so that the plunger would go out further than it normally could, and then ran the engine and waited until the tickover had settled to a normal value.

3. With the engine running I removed the wires from the unit. Note: This will cause a fault to register with the ECU so you will have to remove the battery earth for 15 seconds to reset it.

4. Remove the unit which will now have a fairly well extended plunger.

5. Clean it with brake cleaner and an electric toothbrush (use the SWMBO's - that stuff tastes horrible! ) and fill it with WD40 or similar (don't skimp!).

6. Clamp or block the bypass hose and block off the bypass valve hole (I used a squash ball and some tape).

7. Reconnect the wires to the bypass valve and start the engine with it connected but not installed. At this stage you will see the plunger withdraw as the ecu tries to compensate for low or no tickover.

8. Turn the engine off.

9. Unclamp or unblock the bypass hose and refit the bypass valve correctly.

go for it.

Normal cleaning of the bypass valve would usually (but not always) give me a couple of weeks of fairly trouble-free running. After doing the above I did several months with no problems at all (until the head gasket stopped play).

Hope this helps.

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another point is that usualy the base idle setting needs retunning which should also be done every time the stepper motor is moved and the housing cleaned.

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Can you explain how to retune the base idle ?

Thanks to all for their explanations from a Landy novice !

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Can you explain how to retune the base idle ?

Note:

The 'base idle speed' and the 'idle speed' are totally different things - see below.

Caveat!

Land Rover documentation states something like this:

The base idle speed is set at factory. It should not require further adjustment unless plenum chamber is changed. The adjustment screw is sealed with a plug to prevent unauthorised alteration.

Another caveat!

Before adjusting base idle speed you should check for:

1) Correct throttle cable adjustment.

2) Ignition Timing (or failed Vacuum Advance and/or seized Mechanical Advance unit).

3) Vacuum Leak(s). Check this twice - there are usually some and the really affect things!!

4) Carbon build up in throttle housing, breather hoses, etc.

5) Poor engine condition.

One last caveat:

Before you start, note how far out the adjuster is so that you can set it back there if you hit problems. To do this count the turns to closed and write it down. One situation you may encounter when trying to adjust the base idle speed which may prompt you to just re-set it and walk away, is that if the engine has other 'problems' you may find that the adjuster makes little or no difference anyway. Also, in my humble opinion, base idle adjustment is not necessary if you have only cleaned or replaced the air bypass valve, my reasoning for this is that the first thing you do when adjusting the base idle speed is isolate the air bypass system - however, for completeness...

Background information:

The idle speed on a 3.9 is controlled by the ecu by varying the amount of air passing through the air bypass system. You can think of this as having a similar effect to holding the throttle open a little bit.

If the ecu decides to increase the idle speed for example (perhaps because you have switched on the air-con) it will send pulses to the stepper motor which will withdraw the plunger in little increments - this allows in more air - this is sensed by the hot-wire and so the amount of fuel is increased to match - so the engine speed increases - the ecu detects the increase (via the flyback voltages from the coil) and decides whether the new idle speed is enough - if not it starts the cycle again.

A similar process will reduce the idle speed but the pulses close the air bypass valve a little.

By the above process the ECU will attempt to keep the idle speed at a predetermined level - what this level is is dependent on many factors such as temperature etc but with a warm engine and no unusual loads or conditions, it would normally be about 760
+
20rpm

The ECU and stepper motor are capable of setting the air bypass valve anywhere between completely shut and wide open (which probably equates to about 3000rpm but depends on other things)

The purpose of the base idle adjustment is to ensure that when the air bypass valve is totally shut, the engine wont just stall.

Adjusting the base idle speed on a 3.9 with a warm engine, in neutral (or park) and with everything electrical stitched off:

1. Isolate the air bypass system. This can be done in one of two ways:

1.1. Remove the air bypass pipe (usually just a push fit) and block-off both of the resulting holes into the inlet system. I find a convenient way of doing this is with a couple of pieces of correct sized pipes to slip over the stubs, each with a bolt taped in the other end to seal it.

or

1.2. Use a brake-clamp on the air bypass pipe

Doing the above ensures that whatever the ecu tries to do it cannot affect the idle speed.

2. Locate the base idle adjuster - this is in a hole in a tower on top of the throttle-body. Remove the blanking plug if it is still there.

3. Start the engine (may take a little throttle juggling to keep it going since we are now without the help of the ECU and air bypass system)

4 adjust the base idle adjuster with an allen key to 550rpm (ish) or until the lowest stable tickover is achieved. Obviously this assumes that your engine is not a knackered old nail and that all the usual suspects (above) are checked first.

5. Stop the engine and reconnect the air bypass system.

When you re-start the engine it might rev it's nuts off for a few seconds, but should then settle down under ECU control, to a nice steady tickover again and (unless it was badly adjusted in the first place) you will never know the difference.

There you go - hopefully any errors in the above will soon be spotted and corrected by my peers, and hopefully this will help you with your problem.

Cheers

Roger

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The brain is now going onto overload !! :blink:

Having read all the above many thanks to one and all for the help.

Roger your post was detailed and very helpful...the only problem being that i have the 3.5i and not the 3.9 !

Has anyone an opinion on the idle control valve listed on e bay (370308360463)as it seems a fraction of the price quoted by my local LR dealer !

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Roger your post was detailed and very helpful...the only problem being that i have the 3.5i and not the 3.9 !

As far as I am aware the base-idle principle and procedure is the same..

Has anyone an opinion on the idle control valve listed on e bay (370308360463)as it seems a fraction of the price quoted by my local LR dealer !

Land Rover dealer prices are sometimes quite amazing - over £500 for an alternator for instance. Personally I would be happy with buying the one you mention, since in the past I once bought an LR one at a silly price but found that it lasted no better than a subsequently bought cheap one.

But if you do the rigorous cleaning with the extended plunger as described above, than your old one may well be fine for a long time yet.

p.s. Above when talking about cleaning the stepper I said:

3. With the engine running I removed the wires from the unit. Note: This will cause a fault to register with the ECU so you will have to remove the battery earth for 15 seconds to reset it.

I forgot to say turn off the engine after disconnecting the stepper! Do not disconnect the battery while the engine is running!!!

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