Cutting out: likely causes?

[Mr-Lachs]

Hi all, hope we are well.

As yet I've not actually driven my E30 as yet as it's been in the garage since it got delivered in November. Started it today to come out the garage to sit on the drive for a wee bit (laying flooring in the garage). It starts first breath of the key and settles down to a nice smooth idle, and you get the impression it would sit there all day. However if you pick it up very gently by a few revs, upon releasing the throttle the revs fall away and it drops down below idle and hunts a bit trying to stabilise itself which it does. However if you pick it up a touch more say 1000 rpm upwards and release the throttle the revs fall and it cuts out unable to stabilise itself. This is irrespective of whether it's cold or at full operating temperature. Now I can pick ip up and bring the revs down gradually to around idle and it's ok but if you just release the throttle it will cut out. I'm worried about taking the car out as by the looks of it if I come up to a junction etc it will conk out. What may be the likely causes? Air flow meter or air hoses perished perhaps? I recall my 525i E34 years ago I had to replace the big rubber hose at the meter but I can't recall the car cutting out .

Thanks in advance

Kind Regards

Mr-Lachs

[Brianmoooore]

A weak mixture as a result of air leaks or worn injectors will make it more likely to stall, but the first thing is to check that the throttle position switch is working and adjusted properly.

[Mr-Lachs]

As ever Brian my sincerest thanks to you for this, how do you go about checking (for someone that struggles to open the tool tray in the boot!!) the throttle position switch? Ie where is it, what does it look like, how can i tell if its working, how do you adjust it and what should it be set at? I bet you wished id never asked.... Thank you VERY much in advance.

Kind Regards

Mr-Lachs

[Brianmoooore]

http://www.e30zone.net/e30zonewiki/inde ... ion_Switch

[Mr-Lachs]

http://www.e30zone.net/e30zonewiki/inde ... ion_Switch

Thank you Brian, much appreciated as always

Kind Regards

Mr-Lachs

[Yeti]

fuel pump

[Acaciastrain360]

I had similar problem because I had an 1990 engine with an 1989 maf on it... Replaced the maf to a 1990 and it worked!! Both mafs were fine too

[Brianmoooore]

I had similar problem because I had an 1990 engine with an 1989 maf on it... Replaced the maf to a 1990 and it worked!! Both mafs were fine too

No changes to any AFM for any engine version throughout the production run, except for the deletion of the CO pot on late M40/42 versions.

[Mr-Lachs]

fuel pump

Many Thanks. Hadn't even thought about this due to it starting and idling fine but it certainly could be i guess, i recall the sole time my Dads broke down circa 1995 it was due to the fuel pump packing up.

[Mr-Lachs]

I had similar problem because I had an 1990 engine with an 1989 maf on it... Replaced the maf to a 1990 and it worked!! Both mafs were fine too

No changes to any AFM for any engine version throughout the production run, except for the deletion of the CO pot on late M40/42 versions.

Thats a relief!!

[Brianmoooore]

fuel pump

Many Thanks. Hadn't even thought about this due to it starting and idling fine but it certainly could be i guess, i recall the sole time my Dads broke down circa 1995 it was due to the fuel pump packing up.

I struggle to see what fuel pump fault could cause the symptoms you describe!

[Mr-Lachs]

I had similar problem because I had an 1990 engine with an 1989 maf on it... Replaced the maf to a 1990 and it worked!! Both mafs were fine too

Many thanks for the reply its always appreciated Such a good forum for advice and willingness to help.

[Mr-Lachs]

fuel pump

Many Thanks. Hadn't even thought about this due to it starting and idling fine but it certainly could be i guess, i recall the sole time my Dads broke down circa 1995 it was due to the fuel pump packing up.

I struggle to see what fuel pump fault could cause the symptoms you describe!

I know absolutely nothing about anything mechanical / electrical related, I'm a Polisher so will always listen, but from the little I know the air side of things as you said in your first Reply Brian makes sense, and ill be trying the Throttle Switch first as you have suggested, the Wiki page was very helpful to help someone with as little knowledge as i do to make more sense of things. I think a workshop manual would be a help but in all probability it may get farmed out to someone who knows what they are doing.

Kind Regards

Mr-Lachs

[Yeti]

i had the same issue with my e36 the fuel pump had split at the top causing hesitation engine cutting out as there was enough pressure for it to run but when you accelerate the pressure is increased but the pump couldnt handle it. i changed the fuel pressure regulator,got injectors ultrasonicly cleaned still no luck until i changed the pump. i wasnt saying its the cause but the possibility.

[Speedtouch]

You probably need to re-initialise the ECU.

Disconnect the battery or ECU for an hour or so to reset it, reconnect, let the car idle for at least 10 minutes to enable base idle settings to be learnt. Switch off, then take it for a drive (if possible) throughout the rev range.

This ensures full data transfer from the EPROM chip to the CPU.

[Mr-Lachs]

i had the same issue with my e36 the fuel pump had split at the top causing hesitation engine cutting out as there was enough pressure for it to run but when you accelerate the pressure is increased but the pump couldnt handle it. i changed the fuel pressure regulator,got injectors ultrasonicly cleaned still no luck until i changed the pump. i wasnt saying its the cause but the possibility.

Many thanks for that mate, just shows you anythings possible!!

[Mr-Lachs]

You probably need to re-initialise the ECU.

Disconnect the battery or ECU for an hour or so to reset it, reconnect, let the car idle for at least 10 minutes to enable base idle settings to be learnt. Switch off, then take it for a drive (if possible) throughout the rev range.

This ensures full data transfer from the EPROM chip to the CPU.

Many thanks for this, much appreciated. I certainly had the battery off the car for a week or so until the local BMW dealer got my new one into stock so reconnected it the other day and that was its first start since, though i did notice it was doing this before, the seller charged the old battery before it got collected on the transporter, but it was knackered so i replaced it, but the cars not had a run for at least 3 months now. The chap did say it ran very well the car, usually i guess you can take with a pinch of salt, however the chap and car is known to the zone so have no reason to doubt that it did / does drive well, just with any car of this age it will always have wee teething niggles. Just need to get to the bottom of this one All part of the fun eh.

Kind Regards

Mr-Lachs

[Mr-Lachs]

I must add this is in Park, i have no idea if it does this in Drive but I'm assuming it will make no difference, but I cannot confirm currently.

[Speedtouch]

Cars, particularly big engined ones, don't like being kept sitting about unused for any more than a few weeks - things tend to start seizing up. Best move is to take it for a drive, if possible, and bring everything up to temperature.

[Mr-Lachs]

Very true indeed they do not like sitting I agree, ill need to dig it out when the salts disappeared and give it a good run (if its going to be possible without it stalling all the time. Appreciate everyones help greatly.

Kind Regards

Mr-Lachs

[Brianmoooore]

I was forgetting that this car has been unused, so yes, it might be nothing more serious than the ECU needs to relearn the idle settings. I find that a straight disconnection of a healthy battery doesn't cause problems, but if a battery on its last legs is used to crank an engine until it dies without the engine starting, then the settings will be lost.
A bit of heel and toe driving style might be needed to keep the engine running when you come to a halt might be needed for a few miles.

[Mr-Lachs]

Many thanks again Brian, yes that's exactly what's happened: just before the car was collected the chap said he had charged the battery for me as it was starting to play up, the car arrived and it got taken off the transporter and popped into the garage, I started it a couple of times from November to this month just to keep it ticking over until last week when the car was dead (not even dash lights) so took the battery off and there was a week gap before popping the new one on. I hadn't even gave this a consideration about remembered settings as had thought E30s were pre remembered settings, last time I ran an E30 was about 10 years ago as a daily and never had cause to change the battery: the classics I've had in between have all been carb fed non ECU stuff like Dolomites or Cortinas and it made no consequence whether the battery was off them for 6 months in the winter etc. if that's what it turns out to be (or just for future reference anyway) I'm best avoiding the battery going flat then? Keep it regularly charged (as it is going to be a periodical once a week sort of car), the settings will remain ok if I disconnect a healthy battery to charge it but would vanish with a dudd battery? Or do the settings always vanish when disconnected? Thanks in advance it's mighty useful knowing these wee bits of crucial info kind Regards, Mr-Lachs

[flybmw]

Happy all was solved. Did not know that M42 is settings based ECU. Should take that into account in future.