high idle after HG change-SOLUTION?-

[ratman]

Hallo,
I have a problem:
after head gasket change, I'm suffering a very high idle.
the car stays at 1600 rpm with IAC counting 80 (when engine is switched off) to 3 when is switched on, with the screw on the throttle body fully closed.
If I put the car on service mode (no errors showed), it goes to 2000 rpm. This seems to mean that the IAC is working...

I know that the problem could be caused by air leaks but I tried to disconnect all the vacuum hoses from the plenum, closing with the finger the hole with no success. Anyway 1000rpm difference on idle should mean a huge air leak!

I attached the elanscan and I saw that the TPS is working well, the CTS is good the MAT is good and the MAT is showing 0,4 bar at "idle" (1600rpm) and 0.99bar when the engine is switched off.

what shall i check?

if groundings are not good could be able to cause this problem?
I have a doubt about the grounding of the engine block. the mechanic said that the heart braid was free and he was not remembering where it had to be attached to. So he attached to the chassis using one of the servo fluid pot screw. I know that is should be attached to the chassis
I had no way to find where it is attached to in the standard elans. and so.... where is attached yours??? could you provide a photo??? thanks!!!!

[RayD]

Just a few thoughts ... although you seem to have covered most things.

While you haven’t mentioned it I presume you made sure the cable is allowing the throttle to close.

Does taking a vacuum pipe off cause the revs to rise further?

Do the revs stay the same when the adjusting screw is at 1½ turns out?

Ray

[muley]

To check if it is an earth problem, you could get a booster cable and clip this to the engine and clip the other end on a good earth point...

Jim

[GeoffSmith]

As Ray says, is the throttle cable free and adjusted properly - see the Wiki.

As Jim says, try earthing the engine block and inlet manifold - I don't think the servo fluid pot screw is good enough! Check the Wiki for details.

[ratman]

Just a few thoughts ... although you seem to have covered most things.

While you haven’t mentioned it I presume you made sure the cable is allowing the throttle to close.

Does taking a vacuum pipe off cause the revs to rise further?

Do the revs stay the same when the adjusting screw is at 1½ turns out?

Ray

hi mate, thanks for your help. I try to reply to your thoughts

1: the throttle is closed when the cable is released
2:when I take off a vacuum pipe the revs rise further
3: when I unscrew the adjusting screw the revs rise further to 4000 revs when it is completely unscrewed
ciao!

[ratman]

To check if it is an earth problem, you could get a booster cable and clip this to the engine and clip the other end on a good earth point...

Jim

do you know where is a good heart point? thank you!

[ratman]

As Ray says, is the throttle cable free and adjusted properly - see the Wiki.

As Jim says, try earthing the engine block and inlet manifold - I don't think the servo fluid pot screw is good enough! Check the Wiki for details.

from wiki:
"- An earth braid connects the RH front (rear side) of the cylinder head to the RH end of the chassis front crossmember. "
As you wrote the braid is connected to the engine block and not to the cylinder head. anyway, do you know where is the chassis right point where it should be connected? does you have a photo of the fixing point???
thank you for your help!!!!

ciao, F.

[ratman]

Hi all, I forgot one thing. the car seem to have a good idle for the first 2 seconds after the start up of the engine. only 2 seconds and after starts to raire up to 1600 revs. no idea.... ciao!

[ratman]

I tried this kind of test:
Itook off my car the pipe from the intercooler to the mainfold. To be clear I'm speking about the carbon fiber pipe with the dump valve attached.
I left the vacuum pipe attached to the dump valve in order to close the suction.
the screw on the top is completely closed and the IAC pipe is on the throttle body before the throttle valve
I put a plastic cover on the throttle body when the engine was running idling at 2000 rpm.

I those condition I guess the engine stops in a few seconds.

It was happily running around 1500 rpm.....

the only intake could be the egr or the ventilation valve on the camcover, but they should be closed.
I can imagine only a leak on the mainfold gasket as I can't hear hissings.

what do you think?
thanks for helping.

P.S.: if anybody could make the same test I made, I would be gratefull!!!

[sponcom]

Hi

Did you find a solution to this issue. I seem to be having a very similar problem with very similar symptoms.

Thanks

Paul

[Ian T]

Hi Ratman,

Did you ever fix this?

It sounds like my car has a similar (but not so bad) problem and I have just bought an inlet gasket set to see if the leak is from there. Hard to tell, but I think I have ruled out the other possible causes.

Cheers,

Ian.