E34 535 Idle problem

[Panda]

First Off:

Thank you to everone involved in this site and forum for the effort you put in.
I have been using the site for about 6 weeks since I acquired my 535 and have used it to fix the capacitor problem in the instrument module that seems to be quite common. The repair came in at less than a quid so you guys saved me a lot of time, money and headscratching!

The car has now developed a problem where it tries to idle at 4k. I have replaced the Idle Control Valve but the problem still persists. I have a new piece of ducting (form the air flow meter to the plenum chamber) on order to replace the manky one that's there. I have sealed as best I can the duct to make sure there isn't a leak but am still having the same problem.

Any help/thoughts/suggestions greatly appreciated.

[Gearhead]

Have you pulled all the plumbing off and checked the throttle housing to see if the throttle valves are closing all the way? Sounds like it might be stuck open, so possibly bypassing the Idle Air Control valve entirely. Check things like rusted/bound up throttle cable or cruise control cable, varnish and funk built-up around the throttle valve itself....basically anything that would prevent that throttle from closing entirely.

[Panda]

Thanks for that. I don't think the problem is with the throttle assembly:

If I remove the ICV and put my thumb over the end of its air inlet the idle speed will drop back to normal. Also, with the ICV connected I manually held open the flap in the air flow meter and the idle dropped to around 1500.

Which is the bit I find confusing. In a nutshell....
If I restrict the flow of air in to the idle control valve the revs drop - if I increase the flow through the air flow meter the revs also drop!

[califblue]

mine had a similar problem it was a $60 US part
Crank Position Sensor/Flywheel Sensor for Ignition and Injection

[laguner]

Have you checked for vacuum leaks? You mentioned you needed new ducting and that could be part of the problem?

[Panda]

Thanks Califblue, think you may be right about the crank sensor. Have taken the old one off and have put a new one on order. As an aside the computer has been reset and the display is showing check oil pressure sensor

Does anyone know if it's normal for the teeth on the crank wheel to eat in to the end of the sensor?

[genphreak]

Thanks Califblue, think you may be right about the crank sensor. Have taken the old one off and have put a new one on order. As an aside the computer has been reset and the display is showing check oil pressure sensor

Does anyone know if it's normal for the teeth on the crank wheel to eat in to the end of the sensor?

NO its not, you need a 1.5mm gap (I think) check the Bently- the gap is not critical, but I guess contact could be...

BTW; Triple check your ICV is working to spec also. Get a new one if unsure- it is a wear part. As is the O2 sensor- both should be changed at 160,000km no more is ideal, many say 80-100,000km. In my experience they are seldom done unless ealry on by a dealer.

Oh and double check all suraces the intake boots are sealing- one good leak there can totally wreck the way the EFI (tries) to work. Are they all nice and smooth and round? Nick

[Panda]

Fixed!!!

One crankshaft sensor later. Was quite an easy swap as well.

Thanks again.

[califblue]

Panda, was it the original sensor...mine was