'88 Carrera 3.2 - Throttle idle position switch

[Mike Young]

Hi

I've got an idle problem with my 1988 Carrera 3.2

The car normally idles fine hot or cold. Very stable at about 900rpm. But when drivig the car and you approach a junction for example and take your foot off the accelerator, sometimes the engine just drops straight past the idle speed. Sometimes it will catch itself at about 300rmp and recover, other times it just cuts out. It does this hot or cold.

I've checked and cleaned the air flow meter - that seems fine !
I've cleaned the Idle Control Valve - that seems free enough !

I'm looking at the Throttle Switch now but there are only two wires going to the switch and when I tested them they are connected to the Wide Open Throttle switch.


All the Tech. items I,ve read on Motronic fuel injection refer to the idle position switch !

Can anyone explain whats going on ?
Any suggestions whay my car cuts out ?


Thanks in advance
Mike

[Lorenfb]

There's another switch (idle). Look more closely. It goes to pin 2 of the DME.
Check out this web site (www.systemsc.com) on the Diagnostics page
for some more help & info.

[Mike Young]

Is the idle switch part of the same housing as the Wide Open Throttle switch. There is another switch in the same housing and I can hear it clicking when I move the throttle just off idle. The complete switch housing has 3 connections, the WOT switch deffinately works but there is no closed circut when the "idle switch" clicks.

This would obviously lead me to think the idle switch is faulty - but there is no wire going to it.

Is the "idle switch" you refer to in a seperate housing ?

Mike

[Lorenfb]

You found it. The easiest way to check the idle switch and its' wiring,
is to check it at the DME connector between pins 2 & 5.

[ChrisBennet]

I don't have nearly the experience that Loren has but I'd recommend a slightly different methodology from Loren's.

Loren's method of testing at the DME checks the harness AND switch. It makes sense if you're trying to test if the DME is bad or if the rest of the circuit is at fault. If I was in the DME fixing business I would "cut the problem in half" at the DME connector also. If you find a problem your next step is to check the idle switch. I.e. you're going to be testing the idle switch no matter what.

I prefer to check the idle switch first. I think it is more likely to fail than the harness and it is quicker and easier than messing with the DME connector under the seat.

-Chris

[bigrubberjeep]

Anyone got a picture of this so called switch? I know what the relay looks like, is it the same thing we are talking about?

[Tim L]

Here is a picture from behind the engine, its the black square thing. If you look close its not adjusted correctly. It should be up against the throttle lever.

Tim

[bigrubberjeep]

Oh! Thant thing! It's a micro switch. Thanks fo the info, now I know where to look.

[ChrisBennet]

Originally posted by bigrubberjeep
Anyone got a picture of this so called switch? I know what the relay looks like, is it the same thing we are talking about?

Don't get the DME (grey metal box) and the relay for the DME (DME relay) confused.
-Chris