sudden fault last night....

[stephen318]

as per title my car (318i m40) developed a sudden fault whilst heading home last night.

as i went to pull out from a junction the car starts shunting under acceleration (for those of u that have experienced it, it feels exactly like hitting fuel cut). i managed to coax the car to the side of the road and then discovered that its idle is all to pot, constantly surging from 1500rpm to 3000rpm with a steady rhythm. the car is only driveable using very light throttle, any attempt to use hard acceleration and the shunting starts also it wouldnt rev past 3000rpm in any gear without the shunting coming back. i managed to get it back home ok tho and it starts from hot or cold without any problems but as soon as it starts the idle surge comes in.

now i done some searching today for related problems and the icv seemed a good place to start, so i disconnected it and hey presto the engine starts to run perfectly. i bought a new icv today, fitted it and the problem remains, unplug it and the engine runs perfectly again.

now am i right in assuming there is some other fault causing this and unplugging the icv is masking it???
also am i risking any engine damage by simply running with no icv??

checked the tps and it clicks, also checked all intake trunking and vacuum lines which seem ok with no visible tears etc.
unplugged the afm and the engine died instantly.

any help would be greatly appreciated, cheers,
stephen

[Brianmoooore]

Doesn't fit the symtoms exactly, but check the operation of the throttle position switch underneath the throttle body.
Also, in my experience, an engine will start and idle happilt without the AFM connected.

[stuartgallafant]

sounds like the engine thinks its idling and under load?! maybe there's a chafed wire somewhere on that part of the loom?

[stevo]

could there be a breather blocked somewhere? ive never experienced it in the bm but my old fiesta had a similar problem and it was just the breather pipe on the rocker cover that had a blockage
let us know how you get on