Breakdown

[minesapint]

325i Cab, 1986. 23k
For the first time in 32yrs ownership of my Cab, it’s let me down.
Out on only my second drive of the year after winter layup, and after covering 5 miles the engine died and would only stay at idle revs. As soon as I touched the throttle (even the most gentle touch) it would cough and splutter, could not get revs above 1000. Managed to get home by driving in 1st gear and not touching the throttle.
I removed the ICV, which seemed very dry and its action stiff, I cleaned it and put it back, the engine fired and I could rev it beyond idle speed.
Checked the TPS by listening for the switch to ”aclick”a immediately after throttle leaves throttle body stop, then checked continuity on pins 1and2, short when throttle closed, then o/c as soon as throttle off stop, all seems ok.
Today I took TPS off throttle body to check for oil and grunge in switch, as best I could see there was no oil in switch looked as new, but cleaned with contact cleaner anyway.
Put back together, engine revs fine in garage, no yet taken it out on the road.
Do you guys think I’m on the right track in doing the above, or is there something else I should be looking at. I’m not fully understanding why as soon as I touched the throttle it dies, the TPS when it switches, lets the ECU control the engine speed and takes the ICV out of circuit, is how I understand it operates. If I unplug the ICV at idle the engine continues idling and I can still rev it, is this correct, this seems a bit odd!
Incidentally still got old fuel in tank, but did run for 5 miles, fuel filter changed about 3yrs ago.
Got to bottom this as I cannot abide an unreliable car.
Any thoughts would be most welcome. Thanks

[minesapint]

Come on guys, surely someone must have a view.

[Brianmoooore]

Unplug the AFM and see if that makes any difference to your symptoms.
ICV only controls anything when the throttle is closed. Once the throttle is slightly open, the ICV is irrelevant.

[minesapint]

Thank you for your reply Brian.
With AFM unplugged the car symptoms are exactly as I experienced with the breakdown, when replugged back to normal running.
Can you suggest a solution/repair?
Many thanks.

[BenHar]

It's possible that the connection to the AFM was dodgy and you "fixed" it accidentally when doing the ICV.

Ben

[Brianmoooore]

It suggests to me, that at the time of the breakdown, either the AFM wasn't working, either for electrical or mechanical (barn door jamming against housing?) reasons, or its signal wasn't reaching the ECU.
If the problem has gone away, apart from checking that you can move the door by hand without it catching and applying a little contact cleaner to the plug and socket, there isn't much you can do until the next time it happens, if it happens.

[minesapint]

Again thank you.
Have the AFM on the bench, there is no fouling or play of any sort of the flap, it’s action is very smooth, the whole unit including the electrical socket and it’s plug looks as new.
Are there any other connections in the wiring from the AFM socket and plug to the plug connecting it to the ECU?

[minesapint]

Just wanted to update and complete this post.
I took the lid off the AFM to check internals, no wear to speak of on the carbon track, again all looked as new, resealed. Cleaned plug and socket with contact cleaner, also plug and socket on ECU.



Now driven over 200 miles and it’s not missed a beat, hoping that’s the fault sorted.
Just like to say big thanks to Brian who directed me straight to the fault, your knowledge is invaluable, thank you again.
Cheers

[minesapint]

Try this