M20B25 Intake Air Leaks - Where to start

[capri_rob]

I have what appears to be an air leak as at idle the revs sit where they should be but once warmed up its chugging away rather than a smooth constant idle

So far :

Cleaned ICV with carb cleaner
Replaced Throttle body gasket
Replaced Breather hose from throttle body to cam cover
Checked Hoses from brake servo to TB - all good
Checked Hose from ICV to TB - All good
Intake boot fairly new - no splits - sealed perfectly
Replaced O-Ring from crankcase breather pipe to inlet manifold.
Checked rubber cap blanking cap next to TPS - still present and seems OK

The only thing I havent changed yet is the o-ring at the bottom end of the sprung breather pipe - which of course involves taking the inlet manifold off - again

Sods law says this will be the culprit but Is there anywhere else I need to check for air leaks before I do this ?

Its doing my nut in - as soon as you touch the throttle it sounds fantastic but its ruined by a rubbish idle

[BenHar]

Have you sprayed round everywhere (I use lighter gas, some people recommend WD40) with the engine running?

When you spray near a leak the engine speed will change.

Ben

[maggspower]

Hi there, is the oil filler cap sealed correctly?

You say its worse once warmed up, perhaps a fueling issue caused by the temp sensor?

I know how frustrating these problems can be, sometimes they are a combination of more than one thing, but at least you seem to be narrowing it down. Good luck.

[capri_rob]

Yep - all good for the bits ive checked as above - the only bit I can't get the spray can into ( poor access with everything in place - cant get the right angle on the can to ohit where I suspect the leak is ) is the bottom of the metal crankcase breather pipe - which I'm beginning to suspect must be the problem as everything else checks out

[cecotto479]

Dipstick?

[kam-325i]

Does the idle change when you remove the oil filler cap when its idling ?

[capri_rob]

Dipstick?

Hadnt occurred to me but its seated properly and has good seals - is poor seals on the dipstick a common cause of air leaks ?

It was OK before the head refurb anyway

[capri_rob]

Does the idle change when you remove the oil filler cap when its idling ?

Yes - drops and changes note - supposed to ?

[capri_rob]

You say its worse once warmed up, perhaps a fueling issue caused by the temp sensor?

.

Changed the blue temp sensor for a new one - doesnt seem to have made any difference.

[kam-325i]

Does the idle change when you remove the oil filler cap when its idling ?

Yes - drops and changes note - supposed to ?

Yes......

if it does not change, that is an indicator that there is an air/vacum leak somewhere....

from what you have posted, i would be looking at the Blue temp sensor and checking the operation on the TPS.

EDIT: just noticed you've changed the Blue temp sensor....

might be worth checking the values of the temp sensor at the ECU plug...

[cecotto479]

Does the idle change when you remove the oil filler cap when its idling ?

Yes - drops and changes note - supposed to ?

Yes. And when you pull the dipstick - all are part of the crankcase breather system. The fact that it does suggests that it's venting the crankcase pressure properly.

You're now looking more for "pure" air leaks and possibly a coolant temp sensor issue in my view. Check the resistance across the cts at the sensor and at the ECU.

[capri_rob]

Cheers for the advice

As I've changed the CTS already I was hoping this would have eliminated this as a potential problem but I havent checked the readings so I guess it could be at fault.I kept the original as well so guess I can check it by holding it in a cup of boiling water ?
Is there anywhere else to check for air leaks other than what I've mentioned ?

Intake manifold gaskets all brand new as well and all intake manifold nuts done up properly

[cecotto479]

I was wondering more along the lines of a wiring fault between the CTS and the ECU. Another possibility is the FPR and the vacuum pipe at the FPR OK? I've seen them collapse internally.

Remove it from the FPR and the engine note should change very slightly.

You should feel a vacuum if you put your finger on the end.

[capri_rob]

The FPR pipe isnt the best - I'll have a look at it tomorrow.

The connections at the multiplug under the manifold are all good.

It feels more like an air leak than electrical TBH - its just finding the fecker

[e301988325i]

have you had the co checked on a gas analyser, this will at east tell you lean or rich?

[clipper]

I solved exactly this problem on my car last weekend. The thing is I did loads of things so I don't know exactly what fixed it but here's what I did:

First sprayed carb cleaner everywhere to try to find the source, no luck, so then:

Took out all the intake parts except the manifold.
Re-torqued the manifold nuts (some did turn before torquing up)
Replaced the FPR vacuum line
Fitted new BMW original throttle body gasket
Tightened up the clamps on all the connectors to the brake servo (the original BMW pinch crimp ones)
Re-torqued the rocker cover nuts
Cleaned and reinstalled the AFM, fat hose, throttle body, ICV and all associated pipes

Air leak gone

Hope that helps a bit.

[cro320]

excuse me sir for droping in but I have also slight issue with idle I would like to sort

my idle is steady when car is cold but once it gets fully warm I can see needle very little goes up n down about 1mm, barely visible and engine slightly changes tone.
I checked all vacuum hoses and found small one from FPR to engine manifold to be broken and had replaced but it does the same
Does that mean that I have more leaks?
And one more thing to add...when I rev the engine, and needle drops back it goes to 500 rmp then stabilizes at 750...normal?

[parkin10]

i had leaks on the alloy elbows that go in the throttle body to the servo and the icv alloy elbow
sorted those and now my throttle responce is much better

[clipper]

excuse me sir for droping in but I have also slight issue with idle I would like to sort

my idle is steady when car is cold but once it gets fully warm I can see needle very little goes up n down about 1mm, barely visible and engine slightly changes tone.
I checked all vacuum hoses and found small one from FPR to engine manifold to be broken and had replaced but it does the same
Does that mean that I have more leaks?
And one more thing to add...when I rev the engine, and needle drops back it goes to 500 rmp then stabilizes at 750...normal?

Very, very similar symptoms to what I was suffering until this last weekend, above all the revs dropping to 500 rpm when coming off the throttle. Now my revs drop to 650 and stay there, rock steady.

My layshaft rattle has disappeared too

[capri_rob]

I'm gonna bite the bullet and pull the manifold off again today or tomorrow - I need to satisfy myself that the seal at the bottom of the metal cranckcase breather pipe is good then will go through all the top stuff again.

Hadn't thought of re-crimping the vacuum hoses - worth a go.
The alloy fitting from the ICV into the throttle body isnt particularly tight - might try wrapping it with some PTFE tape to see if that makes any difference.

Will report back later

[clipper]

I'm gonna bite the bullet and pull the manifold off again today or tomorrow - I need to satisfy myself that the seal at the bottom of the metal cranckcase breather pipe is good then will go through all the top stuff again.

Hadn't thought of re-crimping the vacuum hoses - worth a go.
The alloy fitting from the ICV into the throttle body isnt particularly tight - might try wrapping it with some PTFE tape to see if that makes any difference.

Will report back later

If I'm honest I don't think that crimping the servo hoses did much, but tightening the manifold can't have done any harm.

I've never thought that the alloy fittings into the throttle body were a particularly good design... there are 3 in total and on other cars I've seen them gunged up with silicon.
That said, mine are all "natural" and I appear to have no leaks whatsoever.

[capri_rob]

Bastard thing.

Took the manifold off this afternoon - fiddly as fook and hot in my garage - sweat dripping into my eyes after about 15 minutes
Not all the nuts were as tight as I would have liked

Fitted new O-rings to both ends of the crankcase breather pipe

refitted manifold and checked and double checked all the nuts for tightness

Re-crimped the brake-servo hoses

Put PTFE tape round the ICV to TB alloy connection and jubilee clips on the pipes to the ICV

Checked the dipstick - seems OK but might get some new o-rings just to be sure

Checked and cleaned the connections to the multi-plug under the manifold with contact cleaner.

Result - almost exactly the same

I think its very slightly better but its still not a smooth idle.

Pulled the vacuum hose to the FPR - revs changed and could hear vacuum from the manifold - put my thumb over the connection and idle returned to how it was - think the hose is OK.

Crankcase ventilation appears to be working as it should as removing the oil cap or pulling the dipstick out gives a distinct change in idle.

I need to check the CTS and TPS values but I'd lost the will to live after the manifold remove/refit - I was gonna break something

[clipper]

Unless I´ve missed it you´ve not mentioned the rocker cover gasket yet. They have a relitively short life span....

[capri_rob]

Unless I´ve missed it you´ve not mentioned the rocker cover gasket yet. They have a relitively short life span....

Its a brand new genuine one - I can check all the nuts tomorrow I guess - its about the only thing I havent checked.

[cecotto479]

I don't think it'll be the gasket. You'd see oil and it appears to be venting OK or it wouldn't stumble when you open the oil cap etc.

I've seen a wiring fault in the CTS wiring give a faulty reading at the ECU, but fine when testing the CTS.

Not likely, but possible and I spent literally hours tracking it down, so I always check it now. It's worth eliminating it.