Long idle recovery, 3 hours browsing no answer, any help app

[rattysecretagent]

First of all, Start the car once the choke finished idles fine around 800RPM.
Whilst driving everything is fine until you come to stop.

When I put clutch in and come to a stop, in neutral or just on the clutch it will sit at 2000rpm from 5-10 seconds before returning to normal.

Secondly, if I am going down hill / coasting in neutral it will stay at 2000rpm, then again when I come to a stop it will take 5-10 secs to return to 800rpm.

Also in traffic, if I am crawling in 1st with foot of the clutch it will pull me along at 2000rpm until I put my foot on the cluth / neutral and stop, then 5 - 10 secs it will return to normal.

I have an 1989 E30 2.0i touring (manual)

Any ideas as it is only playing up when rolling / moving ?

Thanks
mat

[jimbom30cab]

I had something similar and it was a defective speed sensor (in the diff) which tells the ECU if the car is moving or not. I dissconnected it and it has been normal ever since.

[rattysecretagent]

Cheers dude. I will check that this weekend makes sense. One more thing to try.

[Grrrmachine]

Sounds like a gunked up or broken Throttle Position Switch to me.

[Billwill]

Cheers dude. I will check that this weekend makes sense. One more thing to try.

Might work but you will not have any speedo!

[Billwill]

Sounds like a gunked up or broken Throttle Position Switch to me.

This^^^^ or a sticking throttle cable.

[jimbom30cab]

Speedo is independent of that and still works fine, its just the supply to the ecu I isolated

[suedenim]

Does it idle properly if you lift the accelerator pedal? Mine had a similar problem to yours, after greasing the pedal and putting some drops of oil down the bowden cable sleeve, the problem was alleviated.

[DHFiS]

Throttle cable is sticking or something is preventing the butterfly from closing in the throttle.

[rattysecretagent]

1st answer is correct, you win a prize, thanks Jimbob30cab.

I went to pick up fish and chips, before I left I disconnected the wires from the sensor and you guessed it fixed, (but no speedo and I was doing 0 MPG or 50MPG )

I am an electrical donut, how did you isolate the supply to the ECU ?

Cheers for all your comments

[Grrrmachine]

You haven't fixed the problem; you've masked one fault by introducing another. If the speedo is working on the cluster, then the speedo sensor in the diff is working correctly; it's not a complex mechanism, and it's only two wires.

If disconnecting the diff sensor "solves" your issue, then your problem is something connected to engine managment... such as a bad throttle position switch!

[Brianmoooore]

BMW didn't feed a road speed signal to the engine ECU because they had some copper wire left over. They added the feed because the ECU needs it to operate to its full potential. It's there for a reason, so fix the fault properly.

[rattysecretagent]

Doh

I will have a look and see what I can do to test it ?

If I get it plugged in somewhere will it pick it up, Lie I say when it is electrical I am a donut, Give me a carb or x 4 any day.

[jimbom30cab]

if you want to fudge it properly, I looked on the wiring diagram and found the wire which goes to the ECU after the speedo. I cut it and behind the instrument cluster and put an inline switch so I can make the connection if needed. This kept the speedo and mpg working but allowed me to isolate the feed to the ECU and it idled fine.

Of course I only did this as a temp fix to restore my sanity before fault finding the real problem......honest

The wire is one of those going to the C1 or C2 plug, I can't remember which but it will take minutes to find it on the circuit drawings.

[rattysecretagent]

Hi guys.

Checked the tps wire connections today and all is working fine, between 2,18 and 3.

Still lost as it is so strange, if it was a throttle cable or sticking cable if would return to normal RPM whilst coasting as it does when I stop ?

[jimbom30cab]

take the pipe off the AFM and watch the barn door open and close as you rev the engine to see if anything abnormal happens

[rattysecretagent]

Hi there thought I would let you all know I found the problem sort of ?

I took out and cleaned the relays that sit under the cover between the Air filter and main fuse box, I also cleaned all connections (none of the air related ones as I had done this previously) and sorted, back to normal for now.

Not sure what one it was ?

Thanks for all your help guys, a happy me + happy car

[jimbom30cab]

nice one