High Tickover 1993 2.0 Turbo 940
 

So after my dismal failure trying to cure my cold start issues, now cured by the warm weather, the car has now decided to tickover @1500rpm when it is warm and too high when cool. I backed off the adjuster screw but it made no difference. Throttle butterfly is where it should be and TPS clicks when it should do. If I clamp the IAC hose the engine stops. I believe the ECU controls the tickover it is not actually mechanical, is that correct ??
Any pointers and tips will be gratefully received as always !!

Which adjuster screw did you tinker with Don?

This one, I backed it off but it had no effect. I just pulled fuse 1and 11 and the tickover dropped to a rough 750 ish, took it for a spin and it went back up to 1500, strange.

There is no idle speed adjustment as such, except a base level adjustment to set the throttle body to about 500rpm with the idle valve blocked.

I can think of 2 things

1. No speed signal (it only rasies after you floor it without a speed signal, switch it off and restarting resets it)
2. Too much air (although a leaky inlet would tend to stall with that much air)

I would read the codes first, you don't need a reader, you should have a led flashy module in the engine bay. Its in the 940 FAQ.

If you have a cold start injector, it might be leaking and/or jammed up, then combined with an air leak it could allow a raised idle. I'm just guessing now, but you need to eliminate some issues to narrow it down.

Most 940s don't use a cold start injector, its just done with software, maybe early one have I'm not sure. Could also be the normal injectors, something wrong with them. Try disconnecting each one in turn while the engine is running, if one doesn't make a difference it not working properly.

That's not a very clear photo Don, looks more like a clip to me. As long as you didn't alter the adjustment screw on the throttle butterfly it's retrievable.

Like Tony says ^^^^^ above, there isn't a separate idle speed control, it's set by the ECU. When you say cold idle is high as well, what are you calling high?

It does sound a bit like the speed signal being lost to the ECU, if you can get the fault to happen again, read the codes and see what they show.

https://www.volvoclub.org.uk/faq/Eng...InjectionFault

That's the section you need for the actual codes on yours, read the section above it on how to access the codes if you're not familiar. :thumbs_up:

No codes showing on position 2 or 6.

Yep sorry Dave, sun is that bright out there. It’s the screw and locking nut that point down on the arm. No codes showing. Tickover on cold idle is around 1000 rpm. Didn’t help as the picture spun on loading.

Is the speed signal set by the back axle along with the speedo, if so the speedo is working.

Cold fast idle is about right, maybe a smidge low but certainly in the ball-park. On really cold days i have seen mine closer to 1500rpm if not higher but soon comes down once some warmth gets round the engine and stays around 10-1200rpm until the temp guage starts moving, by which time it's usually dropped to 700rpm as per hot idle specs.

I don't think you've achieved anything with your attempted adjustment of that so let's ignore it for now but may have to ask you for a better pic later, perhaps after dark and use the flash to get a good shot a little further out so it's possible to see what it relates to.



As far as i'm aware, the speed signal comes off the back of the speedo and tells the ECU what speed the car is doing. The idea is it helps with mixture control but i've never worked out the forced high idle except maybe to keep coolant circulating at a good speed to assist in cooling the turbo.
Theory suggests after a few minutes it should reset itself if that is the case but i've found over many years Bosch are a bit light on the obvious side of theory.

What seems to happen on other cars that have had this problem is thatthe signal between the speedo and ECU has been lost for whatever reason, nobody seems to have come up with a definite solution and if they have, they've not posted it but just lived with it.
I'll try and find a diagram later and see if i can work out what should be happening and potential areas to investigate if not.

Try all the positions, I found on the 1991 940 when I read the codes on, the engine slot didn't actually have a pin the other side and it was in another number.