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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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