M40 Low revs, vibrations

[German-Whips]

Hi,

Recently my car has been starting to idle quite low and as a result it sends vibrations through the car. When in drive, it sits around 500 RPM, and in park it sits just over what it does in drive (around 550).
The car is also very hesitant when revved from cold, revs drop as if the car is about to stall, but it doesn't stall.

The vibrations are worse when in drive, but still present when in Park. I've recently had the ICV cleaned by Pacerpete, along with the new gasket and the small rubber pipe.

The throttle switch is now working if that's what it's called (the one which clicks when increasing revs from idle).

It's driving me crazy with the vibrations and vibrating sounds like the dash vibrating around.

Can anyone shed some light on this issue?

Thank you very much!

[German-Whips]

Anyone?

[cypriot_boy_2k7]

you will get more help if this was posted in the techincal section, ask a mod to move it for you

[Billwill]

Take the cam belt cover off to check the condition of the belt and check the cam timing while you are there.

[German-Whips]

Take the cam belt cover off to check the condition of the belt and check the cam timing while you are there.

I think it's the time timing belt needs a change!

Could the cam timing affect my low rev-vibration issue by any chance?

[TPS]

Moved

[German-Whips]

Anyone with some advice please?

[Billwill]

Take the cam belt cover off to check the condition of the belt and check the cam timing while you are there.

I think it's the time timing belt needs a change!

Could the cam timing affect my low rev-vibration issue by any chance?

Is the vibration not coming from a mis-fire at low revs....such as a fouling spark plug?

You need to make sure that while the TPS switch is "clicking" nicely as the throttle is closed completely, that someone has not screwed in the factory sealed throttle stop to attempt to adjust the idle. If this has happened then you will have a large open gap of the butterfly inside the throttle body.

Also check that your ICV does snap open if you briefly apply 12 volts to the contacts and make sur the ICV is insereted in the correct way ie. with the arrow pointing in the direction of airflow into the intake manifold.

Did your M40 behave itself nicely before developing this vibration or did this happen after some work was done?

You can briefly remove all the auxillary belts ( alternator, power steering, air con) to see if the vibration persists...I have seen reports of a bad crankshaft pulley/vibration damper causing vibrations....not sure even if the M40 has a vibration damper!

[German-Whips]

Pacerpete on here had carried out the work so I'm sure its been carried out to a high standard.

However, before this work was done, the TPS switch was not working and as you said someone had adjusted the idle, so it wasn't actaully in fact idling via the TPS function.

Could this messing about have meant there is still a gap in the butterfly that should not be there after the ICV has been cleaned and the TPS made to work?

Also, the vibration is mainly due to the car sitting at a low 500RPM rather than the 700-750 it should be sitting at.

[Billwill]

Have a look at the gap between the butterfly and the throttle body...as far as I know it should be only a very slight, virtually non-existent, gap.

If you do adjust it, first measure the gap with a feeler gauge so you can return it to that same gap if closing it makes it worse.

Haynes does not give a spec for the gap (supposed to be factory set and sealed) and Bentley is pretty useless most times but especially when it comes to M40 engines.