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Will a manifold or inlet manifold leak cause high idle

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As titled really guys, was poking about trying to cure my high idle (1400rpm!) and while I noticed a couple of hoses weren't quite pushed home which bought it down to 1100rpm I could see a bit of smoke at the back of the head

Very hard to tell with everything in place but it appears to be coming from the rear left (as you look from the grille)

Possibly exhaust manifold or may even be inlet manifold gasket.

Would either of these cause the extra 150rpm I'm looking to kill off?

I cant adjust the idle screw any more as its already sitting in its resting position, the appropriate hoses lower the revs on warm up but not once up to temp so I assume this is correct?

Sprayed WD40 on various joints and hose ends but that has no say in revs so they should all be fine

Only really leaves me with the leak I can see, unless the plastic Y-piece has died inside of course

I've tried to photo location as best I can behind the cambelt cover, you can just see some whisps of vapour

20180831_102044.jpg

Current rides:

2003 BMW 330d Manual Saloon Msport
1985 GTI cabriolet black edition (42k miles)
1999 Triumph Daytona 955i Post apocalyptic, rat, brat, scrambler, steam punk, cafe racer

IMG_20190803_123357.jpg

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Bit more hunting and this hose on the back of the head seems to be leaking, bit of a rise in revs when WD is sprayed on it, not going to pretend I know what it is though?

20180831_114630.jpg

Current rides:

2003 BMW 330d Manual Saloon Msport
1985 GTI cabriolet black edition (42k miles)
1999 Triumph Daytona 955i Post apocalyptic, rat, brat, scrambler, steam punk, cafe racer

IMG_20190803_123357.jpg

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Any leaks will indeed contribute to a higher than normal idle. Replace the hose to start with and then spray some brake cleaner around the inlet gasket…a leak isn't uncommon…not much fun to replace though.

www.jmrclubsport.com

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That hose did indeed cause the high idle.
I must of knocked it while putting the mk3 rocker cover gasket on it.

Cleaned up and secured with a jubilee clip and its now at 1000rpm

I expect the inlet manifold leak may be the remaining 50 I need to bring it down but I'm now looking at polishing the inlet with an audi 80 throttle body along with a bit of gas flowing and port polishing to the head so will sort it over the winter while I am chasing a bit more power

Current rides:

2003 BMW 330d Manual Saloon Msport
1985 GTI cabriolet black edition (42k miles)
1999 Triumph Daytona 955i Post apocalyptic, rat, brat, scrambler, steam punk, cafe racer

IMG_20190803_123357.jpg

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Cool well done.

As for polishing….the only thing you'll achieve is a lighter wallet for zero performance gain.

Correct porting however works a treat…it's shape and size you need to achieve, with a satin smooth finish all you need to aim for….if you don't remove and re shape material you'll gain nothing in flow and subsequently any extra power.

I did a customer head and cam combo for his cabrio a while back, made a genuine 132hp on a std DX bottom end with gains right up through the rev range. Only the throats and valve seat angles were re shaped, the ports including the inlet manifold left totally std as the owner wanted improved performance rather than bigger numbers.

On a std engine all that's gained from fitting a bigger throttle body is an increased rev range…peak power tails off a couple of hundred rpm later but the peak number doesn't increase. They do however work better the more you ask from the engine in terms of power.


www.jmrclubsport.com
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