hi everyone could do with some advice from people who know more than i do.The problem is on my M reg V8 when i start it up it revs to about 2500 revs for about 20 seconds then drops off slowly to just below 1000 also sometimes not very often it revs like mad when i put it in park (auto box seems spot on) just passed its mot with no problems dont have a clue whats going on also when i take the petrol cap off it hisses like a tyre going down is this normal other than that its all good any ideas would be greatfully receved cheers paul
Tubes63
New Member
I think the high revving for 20 seconds or so is pretty normal (happens on mine but I've had so many problems lately I just assume anything my car does is wrong haha). If it's a new thing then you might have a vacuum leak somewhere or a faulty stepper motor, but someone with superior knowledge to me will come along soon and probably tell me I'm wrong 
. One bit of info might be useful, if you get the engine warm, turn it off then turn it on again does it still rev high for 20 seconds? I suspect it won't as I think the high rev is just a way to get the engine initially warmed up.
When you say it revs like mad when you put it in park do you mean it surges up and down, or do the revs just go high and stay high?
I do know that the hissing when you take the petrol cap is taken off is quite normal. Mine does it, and I remember reading a thread here a while back about someone asking the same thing, with most people agreeing that it's normal.
. One bit of info might be useful, if you get the engine warm, turn it off then turn it on again does it still rev high for 20 seconds? I suspect it won't as I think the high rev is just a way to get the engine initially warmed up.When you say it revs like mad when you put it in park do you mean it surges up and down, or do the revs just go high and stay high?
I do know that the hissing when you take the petrol cap is taken off is quite normal. Mine does it, and I remember reading a thread here a while back about someone asking the same thing, with most people agreeing that it's normal.
hi thanks for the reply to answer your questions first it always does the reving thing on startup hot or cold as for when its in park it goes high and stays high i have to put it back into drive and then back to park and that seems to put it right like i said i'v no idea.It passed the mot with no adviserys 2 weeks ago but the guy at the garage said he had to "tinker" with it to get it past the immisions test and charged me £88 for the privilege other than that he said it was spotless but he did say about it reving on start thats why im asking about it to see if its normal or not thanks again paul
I'd disagree that revving at start-up is normal at all, and having to go from drive to park to drive to park again is just plain wrong!
Dunno what it is, and I don't know the v8's at all really other than I luuurrve the noises and the power of a well sorted one, but I'd start looking at linkages and connections, auto kick-down cable tight or loose for instance, check filters, air, fuel and oil. I'd also research the choke cable (if it has one) or the choke function and see how that works and check it's function.
Dunno if the throttle on V8 is fly by wire, but if it is I'd also check TPS, if it's a 'normal' cable, then I'd check the cable runs freely, fill it with WD40 maybe, and check the connections at each end for fraying and the linkages to it for binding.
Sorry I can't be more specific ..
Dunno what it is, and I don't know the v8's at all really other than I luuurrve the noises and the power of a well sorted one, but I'd start looking at linkages and connections, auto kick-down cable tight or loose for instance, check filters, air, fuel and oil. I'd also research the choke cable (if it has one) or the choke function and see how that works and check it's function.
Dunno if the throttle on V8 is fly by wire, but if it is I'd also check TPS, if it's a 'normal' cable, then I'd check the cable runs freely, fill it with WD40 maybe, and check the connections at each end for fraying and the linkages to it for binding.
Sorry I can't be more specific ..
discool
Well-Known Member
I assuming you have a 3.9 and running normally you will have increased revs when starting cold or hot.
Cold around 1500rpm for 10 or 15 seconds and dropping down to around 650-700 , and around 1000rpm dropping to idle in around 1 or 2 seconds when hot the correct idle speed band in shown for an auto is 665 to 735 in neutral.
You engine speed at idle is dependant on the setting of your base idle and then the ECU takes over the settings.
Anyway your problem, check the crankace breather and its hose to the plenum chamber is clean and also you dont have any air or vacuum leaks.
When in the past and even in my 3.5 days I found the idle speed is playing up I have just stuck some fuel treatment in the tank after cleaning the breather and all was well.
You can go deeper into the workings by checking your idle control valve (stepper motor) is clean and by resetting your base idle.
If you still have the same issues then you will need to get the ECU pluged in and tested unless you wish to replace parts on a trial & error bases.
Cold around 1500rpm for 10 or 15 seconds and dropping down to around 650-700 , and around 1000rpm dropping to idle in around 1 or 2 seconds when hot the correct idle speed band in shown for an auto is 665 to 735 in neutral.
You engine speed at idle is dependant on the setting of your base idle and then the ECU takes over the settings.
Anyway your problem, check the crankace breather and its hose to the plenum chamber is clean and also you dont have any air or vacuum leaks.
When in the past and even in my 3.5 days I found the idle speed is playing up I have just stuck some fuel treatment in the tank after cleaning the breather and all was well.
You can go deeper into the workings by checking your idle control valve (stepper motor) is clean and by resetting your base idle.
If you still have the same issues then you will need to get the ECU pluged in and tested unless you wish to replace parts on a trial & error bases.
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Try giving the idle bypass valve a good clean with brake cleaner or carb cleaner. Don't be shy at spraying it in there thy get really gunked up.
I had a 3.9 range rover with similar symptoms to yours and that cured it.
It could be a vac leak somewhere but try the easy stuff first. Good luck
I had a 3.9 range rover with similar symptoms to yours and that cured it.
It could be a vac leak somewhere but try the easy stuff first. Good luck
