318IS revs dropping off, then stalling. possible misfire too

Post Mon May 11, 2015 9:46 pm

So I'm hoping you can help me with the issue I'm having.

Two weeks ago I took a short 3mile journey when the car was cold to pick up dominos for lunch, on return to the car it would only start when giving it some revs else it would stall instantly.

I kept the revs up for a bit then it stopped stalling but idled at 1.5k roughly a mile down the road it started idling fine again, so just put it down to I'd done a short journey and it being an old car...

Anyway, fast forward to this afternoon, I bought a chip from Speedtouch off here and installed it. Upon following the instructions, leave to idle for 10mins, after around 3-5mins it starts dropping the revs to around 200-300 then picks back up then drops again and after doing this it eventually stalls - when the revs drop off it feels/sounds like its misfiring.

After around 10mins I took it for a drive and when I'm giving it some, its bloody great (once it decides to pick up and give power), feels so much more responsive. But as soon as I start cruising or start idling it goes back to running rough and eventually stalls again.

I cant see how this is down to the chip since I'm sure a lot of other people run this? So has this made an issue I have worse when installing the chip?

Any ideas of what it could be, heres a video of it idling -

I'm hoping someone has experienced this before and can tell me what it is?

Post Mon May 11, 2015 9:56 pm

It could be the AFM, M40/M42 AFM are known for making any kind of crappy things at idle, that's why BMW published a SI regarding this and made a recall to install an adaptor harness between the AFM and the car harness to filter the AFM signal. Is your car catalysed? Try to start it with the AFM unplugged and see if it idles better.

Post Mon May 11, 2015 10:03 pm

DaniTD wrote:It could be the AFM, M40/M42 AFM are known for making any kind of crappy things at idle, that's why BMW published a SI regarding this and made a recall to install an adaptor harness between the AFM and the car harness to filter the AFM signal. Is your car catalysed? Try to start it with the AFM unplugged and see if it idles better.

I believe it is yes, the thing just after the airbox?

EDIT:

Just unplugged it, it idles spot on, but then doesn't like revs - this correct thing to happen?

Ran it for 10mins before I attempted the rev.

Turned off, the plugged it back in, idled like a pig but revs fine.

So think its definitely that? correct characteristics for when unplugged??

Post Tue May 12, 2015 10:15 am

Its normal that the engine revs like crap when you disconnect the AFM as these cars doesnt have a throttle potentiometer (only a switch). Maybe you should do some electrical test before ruling out the AFM. You can try to connect a voltmeter between pin 2 and 5 of the AFM (they're labeled), put key on ignition but do not start the engine and move by hand the internal flap of the AFM (for this you will need to unscrew the AFM from the air box) As you open the flap you should see an steady increase from 0.24 to 4.75v aprox. There should be no flat spots or random values. This can be seen better with an analog voltmeter (if on a certain point, maintaining the flap stopped, the gauge gets crazy or you have a zero value, then the AFM is toast (although you can do some adjustments and try before replacing it).

Post Tue May 12, 2015 10:31 am

DaniTD wrote:Its normal that the engine revs like crap when you disconnect the AFM as these cars doesnt have a throttle potentiometer (only a switch). Maybe you should do some electrical test before ruling out the AFM. You can try to connect a voltmeter between pin 2 and 5 of the AFM (they're labeled), put key on ignition but do not start the engine and move by hand the internal flap of the AFM (for this you will need to unscrew the AFM from the air box) As you open the flap you should see an steady increase from 0.24 to 4.75v aprox. There should be no flat spots or random values. This can be seen better with an analog voltmeter (if on a certain point, maintaining the flap stopped, the gauge gets crazy or you have a zero value, then the AFM is toast (although you can do some adjustments and try before replacing it).

Speedtouch advised of this, and I was going to do this -

tonight and see if it makes a difference?

Post Tue May 12, 2015 11:20 am

Thats the adjustment I was talking about to do before replacing the AFM, I only told you a way to test if this is necessary a˜ƒ

Post Tue May 12, 2015 11:36 am

DaniTD wrote:Thats the adjustment I was talking about to do before replacing the AFM, I only told you a way to test if this is necessary a˜ƒ

Great I'll try this for sure. I'd like to save £200 on a new AFM!

Question, this could be related.

So when we were driving the car back, my dad put his foot down to overtake on a dual section, revs went stupid high and car went no where, so my dads first thoughts were the clutch is slipping?

Couple days later I used the car for work, and car pulled strong no issues as described above, but then on the drive home it did it.

So it doesnt always do it etc so makes me think its not that.

My mate mentioned it could be a sticky thrust bearing as old BMW's were prone to this?

Also another thing I noticed is when I put my foot down it struggled sometimes to give power revs would drop down then go up slightly then pick up? I'm assuming this issue could be along the lines of the AFM failing?

I'm hoping the adjustment tonight will fix a lot of my issues and get the car running smooth, the chip is great from what I've experienced so far

Post Tue May 12, 2015 9:13 pm

DaniTD wrote:BMW published a SI regarding this and made a recall to install an adaptor harness between the AFM and the car harness to filter the AFM signal. .

Have you got any more info on this?

Post Tue May 12, 2015 10:02 pm

I had it somewhere but I can't find it - it's reference was 13 03 91 (3290). If I find the copy I'll send you

Post Tue May 12, 2015 11:45 pm

So I adjusted the AFM, but it kept happening, so I've removed the chip and it's driving like it use to again.

I really enjoyed the responsiveness of the new chip though

Post Wed May 13, 2015 12:40 am

DaniTD wrote:Its normal that the engine revs like crap when you disconnect the AFM as these cars doesnt have a throttle potentiometer (only a switch).

iS has a pot., not a switch.

smithsOn wrote: I've removed the chip and it's driving like it use to again.

There are differences between the ECUs fitted to the iS, which means that there is no one replacement 'chip' that will work with all ECUs. Posts like yours, regarding a 'chipped' iS are not uncommon.

Post Wed May 13, 2015 7:54 am

Brianmoooore wrote:
DaniTD wrote:Its normal that the engine revs like crap when you disconnect the AFM as these cars doesnt have a throttle potentiometer (only a switch).
iS has a pot., not a switch.

smithsOn wrote: I've removed the chip and it's driving like it use to again.
There are differences between the ECUs fitted to the iS, which means that there is no one replacement 'chip' that will work with all ECUs. Posts like yours, regarding a 'chipped' iS are not uncommon.

Sorry, I thought it was a 318iS, not a 318is (at least here in Spain there are the 318i M40, 318iS M40 with sports package, 318iE with luxury package and the 318is with M42). Yes, the 318is has a M42 with Motronic 1.7 which already uses a pot.
Anyway, it could be normal that it runs like crap without the AFM as the ECU can't know the real load of the engine. But with a chipped ECU, who knows