318i M40 Idle Problem

Tue Apr 05, 2005 4:00 pm

I have a very annoying problem with the idle on my 1989 318i M40 engine. It never idles above about 650rpm when warm and quite often when depressing the clutch to approach a junction the engine almost dies and occasionally it actually will stall.

On some occasions when starting the engine it will start to surge between about 650 and 1500 rpm before eventually settling to about 650. Sometimes it will immediately surge to about 2-2500 rpm but will eventually slow down to about 650 rpm. Sometimes it just does not want to idle at all after starting. These problems usually occur when starting the car after it has been left for about an hour after being hot.

I have setup the throttle stop and TPS as specified and cleaned the throttle body throughly. The ICV is ok as I have swapped it with another one to confirm. The air flow meter has also been swapped with no change. The ECU has been swapped with no change. I have thoroughly checked for air leaks with carb cleaner to no avail. I have also replaced the large air hose from the AFM to the throttle body.

My BMW specialist thinks that it maybe an intermittent wiring problem with a feed to the ECU but it is not economically practical to diagnose this. I have manually checked the wiring as best as I can without seeing any problems. The only other thing I can think of is the coolant temp sensor but my temp guage works fine so I guess it is working OK.

Does anyone have any ideas please as I seem to have exhausted everything?

Thanks

Tue Apr 05, 2005 4:07 pm

The thing is the throttle stop and TCP should never be adjusted, you have messed the settings up.

If i were you a new TB thats not been messed with is an idea, then start again.

Andrew

Tue Apr 05, 2005 4:11 pm

Ok fair enough. Problem was that the throttle stop was messed around by someone else. I have set it up as it should be:

Disconnect ICV, TPS

Adjust throttle stop until idle speed about 750 rpm

Adjust TPS so that clicks just as throttle is opened

Reconnect ICV, TPS

Tue Apr 05, 2005 4:19 pm

Yeah if the Ecu learned the TPS possition. On the M40 it doesnt, the throttle should be shut 100%. The ICV should then give all the air to keep the engine running.

Andrew

Tue Apr 05, 2005 4:54 pm

Mine did this.

I thought it was the butterfly not closing all the way shut when the pedal was released. I tightened the throttle cable just a little bit flicked the butterfly open and closed a few times to make sure the idle switch was closing and it seems ok now. touch wood it will be. I haven't had it do this since but the problem was intermittent anyway.

I may be way off base here. So please somebody shoot me down if I am

Tue Apr 05, 2005 5:01 pm

Ok, I have checked and adjusted the throttle stop so that the butterfly is completely closed. It still does not idle any higher though. Even when starting from cold, it initially revs at around 800 rpm although within 30 seconds or so it goes back down to about 600 rpm. Is this correct?

Tue Apr 05, 2005 5:13 pm

Now you need to tweak the TPS till you can hear a click.

Its hard to explain but you need to adjust it so that when the throttle opens even slightly there the TPS produces a click. You can do this by un doing the two screws and rotating the TPS. You may also have a AFM issue.

Andrew

Tue Apr 05, 2005 5:15 pm

Sorry, I should have said that I have done this as well. I have it all set up as it should be with the TPS clicking when the throttle is opened very slightly.

I'm pretty sure it is not the AFM as I have swapped it for another one and the problem is identical.

Tue Apr 05, 2005 11:19 pm

Is it possible the tps itself is faulty?

Give me a shout tomorrow and I can take readings or give you pinouts from mine should you need it.

Tue Apr 05, 2005 11:55 pm

TPS can easily be faulty. Take of the big air hose if necessary for access, and check the switch with an ohmmeter.
Pins 1 and 2 should be short circuit at no throttle, and open just as the throttle moves.
Pins 1 and 3 should be normally open circuit, but short circuit at approaching full throttle.
Concerning the coolant temp sensor. The one that works the temp gauge (brown) has no connection at all with the one that controls the ECU (blue). Don't think your coolant sensor is the main cause of your problems, but it might be a bit out of spec and not helping. Cheap and easy to replace if the TPS proves blameless.

Wed Apr 06, 2005 12:37 am

Ive had similar problems with my motor (same engine)

http://www.e30zone.co.uk/modules.php?na ... pic&t=3530

I start it, and basically everytime i do so it stalls (it was fine when i got it, just a bit low idling somtimes, not its so bad its all the time) . It runs at 500rpm or lower, probably about 400rpm, and i have to rev the bullocks off of it and at every junction for the first 10 minutes or so i have to clutch it and rev and brake, not very practical,but if i dont i can garrentee it stalling.

When im stationary and its doing it,it sounds like its going to stall ,thenit struggles to keep going, turns over a few times, and then dies.

Ive got a new ICV comming, and i replaced the big intake hose thinking their may be a leak but it didnt help

Wed Apr 06, 2005 6:53 pm

Brianmoooore wrote:TPS can easily be faulty. Take of the big air hose if necessary for access, and check the switch with an ohmmeter.
Pins 1 and 2 should be short circuit at no throttle, and open just as the throttle moves.
Pins 1 and 3 should be normally open circuit, but short circuit at approaching full throttle.
Concerning the coolant temp sensor. The one that works the temp gauge (brown) has no connection at all with the one that controls the ECU (blue). Don't think your coolant sensor is the main cause of your problems, but it might be a bit out of spec and not helping. Cheap and easy to replace if the TPS proves blameless.

Ok thanks. I have checked this before when I initially set up the TPS / Throttle Stop. It was as specified.

Do you know if you have to drain the coolant to replace the blue temp sensor? Thanks for the info!

Wed Apr 06, 2005 8:28 pm

No need to drain the coolant to change the blue sensor,although IIRC it's a bit akward to get at on the M40.
You will loose a bit of coolant changing it, so top up the header tank a bit before you start.

Thu Apr 07, 2005 12:26 am

Whats all this about the TPS and throttle stop? Is this a possible cause for me as well maybe?

Thu Apr 07, 2005 9:43 am

Brianmoooore wrote:No need to drain the coolant to change the blue sensor,although IIRC it's a bit akward to get at on the M40.
You will loose a bit of coolant changing it, so top up the header tank a bit before you start.

Ok thanks a lot. Will get onto it as soon as I find time to go and buy a new sensor.