Strange idling 1998 940

[93Regina]

LH 2.4 ECU,

Another quick test - When engine is at operating temperature, and when idling (vehicle stopped), disconnect IAC plug from IAC...and drive on

Note - I've never tried this, but IAC does allow air to flow thru it...so RPM will change, but how much, I don't know.

[98945lt]

Thank you for tips.
Yes I will try that.

[98945lt]

One another thing:
Today i pulled out the fuse for abs, no different.

[93Regina]

tips

Throttle plate must be within OEM spec...along with throttle switch....this is explained here.

[98945lt]

Yes. I have adjusted that "by the book".
Have also replaced the tps with a new one.

[93Regina]

I have adjusted that "by the book".

IIRC, once engine is above some RPM (i.e., vehicle is moving), IAC may be de-energized...but I've never tested IAC to see if this happens. IAC is just for idling.

I assume a postive voltage is always present at IAC, and it is activated via ground pulses.

So, what is idle RPM with IAC plug disconnected? When engine is cold, and when its upto operational temperature?

[98945lt]

Been busy with working last days. Hope I can get time to test your tips later today.
New experience earlier today:
After engine is on operating temp. and the idling is high (1200-1500 rpm), I stoped the car (Note: not the engine), stood still for about 5 sec. and start driving again, then the idle was almost normal (below 1000 rpm.) the rest of the trip, almost 40 km.
Have study wiring diagram. Wires from abs/speed sensor is going to abs control unit and the speedometer and, if I read the diagram right it goes wires from abs unit to the LH2.4 unit. Is it possible that the abs unit is failing even if the abs lamp is dark and no error codes and this fail results in strange idling?????

[93Regina]

...if I read the diagram right it goes wires from abs unit to the LH2.4 unit. Is it possible that the abs unit is failing even if the abs lamp is dark and no error codes and this fail results in strange idling?

Try unplugging IAC first...we need to find out if IAC is causing the issue, which would mean your ECU/etc is involved. If so, we need to eclectically verify your TPS is working correctly.

Art Benstein might know more on abs/speedo question...his email address is at bottom of page. But, see above...basic grunt work needs to be done before contacting Art.

[98945lt]

Have unplugged IAC and rhe was rising up to about 2500 rpm. Have also tried a new IAC.
Have change the abs-computer (left driver side) and the became much mire normal, but it still about right above 1000 rpm and goes down when rhe car stops.
On my diagram it gows a wire from soeedometer via fuse boks to abs transient surge protector. Do you know what function this have and where it is placed??
In the abs modulator it is two relays, do you know what function these relays have?

[93Regina]

unplugged IAC and rhe was rising up to about 2500 rpm.

Leave unplugged, and adjust throttle plate to say 1,200 RPM


Note - If you have vacuum leaks, then fix them