M40 Intermittent stalling & idling issue

[cmsslee]

Hi all, hoping for some pointers in which order to start tackling potential causes for a problem with my M40. I have searched the forum and whilst there are loads of threads on idling/cutting out issues I couldn't see one that was exactly like mine...

It's a 318i convertible that had been standing for over 18 months until recently. With the body work finished I had it serviced and MOT'd last week and picked it up last weekend. The idle was a bit lumpy, felt like it was going to stall but didn't - there was nothing but fumes left in the fuel tank so filled her up and hit the road. Did approx 100 miles of motorway and urban driving and it was running lovely and smooth, revving freely and idling perfectly at standstill too, both from cold start up and when the engine was at normal operating temp.

Then yesterday I was driving home from work and every time I slowed before coming to a standstill (junction/lights etc.) the engine stalled. It started again without any problems and as long as i gave it a bit of throttle it was fine to idle/pull away. Then when I got within half a mile of home and pulled up at some lights it didn't stall, it did a bit of a mad idle (repeatedly engine almost stalling followed by increase revs) which I recorded on my phone, engine was really shaking. Here's the video:

http://youtu.be/i1Vde5u_YrU

Following that I arrived home and in typical fashion it was idling perfectly again and was really smooth. The wife took the car to work this morning and reported back that it was running perfectly.

If any of you helpful chaps can let me know in which order I should start tackling things to solve this it would be much appreciated. I'm a total spanner novice but willing to get stuck in

[Billwill]

Check for air leaks around the intake gaskets, all the rubber hoses in that area including the hose to the camshaft cover and the brake booster....spray Carb Cleaner around these areas and if the idle changes then that area is bad.

Remove the ICV....metal/plastic cylinder plugged into the bottom of the intake manifold up against the right side bulkhead. Give it a good cleaning and a spray of W40...if you briefly touch 12 volts across the terminals it should snap open and shut cleanly. Make sure you put it back correctly with the arrow showing the direction of airflow.

Make sure the Throttle Position Switch (TPS) is working properly. It sits under the throttle body and lets the ECU know when you are at idle....as you relax the throttle completely you should hear a "click" coming from the switch...some owners try to adjust the idle by moving in the factory set throttle screw that opens up the butterfly somewhat....this stops the TPS from clicking.

With the engine standing so long there may be rust in the fuel tank clogging things up and the fuel filter may be clogged up.

Check the plugs are OK...I find my M40 only likes NGK plugs.

[aimlessrock]

big Wills advice above should help, when was the last time the injectors were overhauled ?

[cmsslee]

Thanks billwill I'll start there. Like I said I'm a pure novice but if it was fuel related wouldn't it be doing the same thing right through the rev range?

Good to see a fellow Manchester based zoner aimlessrock - where are you?

[markus_74]

check first the spark plug color and if any different it could be any cause, like injector clogged or ht lead etc.