Speedometer 940

[98945lt]

Vacuum hoses are repkaced, also checked with spraying start gas.
Lambda is replaced and coolant level is fine.
Have also replaced iac, amm, tps, LH 2.4 unit with new chip, cts and speed/abs sensor in diff.

[Laird Scooby]

Originally Posted by 98945lt

Vacuum hoses are repkaced, also checked with spraying start gas.
Lambda is replaced and coolant level is fine.
Have also replaced iac, amm, tps, LH 2.4 unit with new chip, cts and speed/abs sensor in diff.

When you say "replaced", was that with new or secondhand parts?

Also have you tried cleaning the throttle body? Also the PCV valves/hoses etc?

There are a few other possibles but let's get the basics right so they're eliminated then go onto the more complicated stuff.

[98945lt]

Yes. The repkaced parts is new, original parts, also PCV is replaced with new and hoses checked. First thing I did when this problem occured was cleaning the throttke body. It was almost no dirt in it, but I did it for sure.

[Laird Scooby]

If memory serves correctly there are two CTS sensors - one for the instruments (temp gauge) and the other for the engine management/LH2.4 ECU. Can you remember if the sensor you changed was a 1-wire or 2-wire sensor?

[98945lt]

That's correct and I replaced that with two wires, that who is placed longest behind, I think I remember aprox. between syl. 3 and 4. No error codes is stored, but maybe that makes sence because errir codes are tested when tje car is standing still, and the idle is act normal when the car is standing still.

[Laird Scooby]

As far as i know the ECU constantly monitors for faults so it can respond to them sooner rather than later.

That aside it sounds like it's something simple that's been overlooked - perhaps lubricate the throttle cable, throttle linkage, kickdown cable (if it's auto) and also check the vacuum hose that feeds the EZK ignition control unit.
On UK models it's under the dashboard on the right, i don't know if it's in the same place on left hand drive cars or whether it is moved to the opposite side.

What i'm thinking is it may be kinked or squashed so as the vacuum builds in it for the ignition advance it stays there causing a high idle speed. If you switch off it gives it a short while for it to dissipate so when you restart it goes back to how it should be.
It may be that the hose has come off the end of the stub it fits onto on the EZK ECU which caused similar problems on one of my 740s, refitted it and problem solved and a much livelier/more economical car as well!

[98945lt]

Us there a vacuum hose fitted to the EZK ECU?? I didn't know that. Where is that hose coming from? Do you hav a picture etc. who is showing were it'is fitted on EZK?
Thank you!

[Laird Scooby]

The easiest way to find where it comes from is to find the EZK ECU under the dash and firstly make sure the vacuum hose is connected then follow the hose up to the bulkhead, find it the other side in the engine bay and follow it to the inlet manifold.

Whether it is the engine or air filter side of the throttle body i can't be sure but it's usually somewhere near the throttle butterfly.

As for photos, it's about 5 years since my last 740 and if i had any photos they would have been lost because of photobucket. I may have them somewhere on a PC or USB stick but where i haven't a clue!

[98945lt]

I see! My car/engine is running pretty good, no problem with startin up cold/hot, but anyway I'll take a check on this.
Thanks for the tips!

[Laird Scooby]

It won't cause starting problems as the vacuum will leak away from the kink/squashed part (assuming that's what it is) while the engine is off but it could be holding on to vacuum after a bit of running because of the restriction.
That would cause the idle speed to come up, for a while at least and depending where it picks up on the inlet, could be maintained at an incorrectly high level until you switch off for a few seconds.

I might well be wrong on this but it's worth a look.