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PeteMck

Rover 4.6 V lumpy idle then revs by itself

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Ah yes, different on that plenum, I forget how it is supposed to be, will look up later.

Any chance you have excessive crankcase pressure?

 

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Well I'm not gonna rule anything out but it's a brand new recon engine so I hope not! Lol. How can you tell if there's excessive pressure? 

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Remove that hose and check for excessive puffing, but if a new engine,don't worry about it :) 

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If there is an air leak into the crank case.

So... On that note, what is the disptick seal like?

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Does that drill bit seal properly?

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Drill bit has been replaced with proper pipework now. Dipstick seal is pretty good. 

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Still struggling to find the vacuum leak. It actually idles pretty well until it gets up to temp then it wants to be around 1000rpm to run well. Have checked the butterfly valve in the plenum and that seems fine. Could it be the seals where the butterfly valves connects to the throttle linkage and tps sensor? 

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Yes, I ha e had that cause problems before, about £15 to refurb from memory.

The left hand breather, where it connects to the plenum, is that restricted in the same way as the right hand one?

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I can't remember if it is or not. It enters in front of the butterfly valve though I think. I've changed the valley gasket today as now working my way up and the rocker covers seals as well. One thing I did notice this morning is that when starting from cold it idles well until it starts to warm up and only really starts hunting when it's up to temp. Don't no if that helps narrow down the causes.

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Sorry, getting my left and rights mixed up! The right hand breather, but guess you have answered that one...

I went to a 3.9 setup, which links the two breathers into one port. Is the top end all 4.0 stuff, or a mixture?

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Everything is 4.6l stuff apart from the exhaust manifolds which are 4.0l 

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Right, had the tps sensor off and the stepper motor out. Tried blanking off the stepper motor but it just started reving to 2000 on idle so put it back. Is it possible I've got an air leak around that internally? 

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Right, slight update. Ive got another plenum and tried that incase I had an air leak where I'd put all the pwm pipe work on or incase I had a leak around the throttle housing and still got the same problem. Starting to run out ideas as to where to look for an air leak. 😖

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I haven't read back through this but by blanking off the stepper do you mean actually blocking the air passage or just blanking the place where the stepper goes?

Need to break this down methodically bit by bit to rule stuff out.

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Yer well I was wondering if I had a leak with the plenum (blanking plugs, throttle housing, stepper motor wasnt shut fully, where I had mounted niges pwm pipe outlet etc) so put another plenum on and still got the same problem. I can find any air leaks anywhere incl rocker cover pipes, changed valley gasket, rocker cover gasket, I've blocked off the brake servo pipe incase that was leaking and it's still wanting to idle around 1000rpm

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What did you do with the old stepper to make sure it is closed? The one behind the drill bit in recent pic?

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Errr just assumed it was fully shut in its 'resting' position. From memory they are sprung arnt they? Either way the other plenum had it's own one in and still the same issue. 

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Nope.

You need to do something with it, this is 99% likely your problem....

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Hmm when you say do something? Just start poking it with some electricity and see what happens? 

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No, remove and work out how to plug the hole.

It's a stepper motor, so poking with 12v won't do anything.

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I don't remember what it looks like behind there, over to you I am afraid :)

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I seem to remember that the stepper allows air from a port coming in from the main throat of the plenum (concentric to the stepper hole) to take a 90 degree turn through a small port on the inboard side. You'll need to jam something in to block both holes- I think I wrapped a drill bit in insulation tape until it was a snug fit when I set my base idle.
 

This was all quite a while ago though so I may be talking total piffle.

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