High idle, around 1500, so I used the OBD to check the Idle Air Control. Did not function during test so I swapped out one from the parts and no change. Tried a spare ECU and that solved the high idle.

Any thought about what to do with the now defective ECU?
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89 240 wagon, 94 940, 300K, 94 940, 141K

Hi,

When is hear someone say that they are having a high idle issue I ask where or how does the engine get the extra air to run faster?

I agree with Volvo From heck or Dave on this one. Probably a bad connection somewhere or a split hose along the line of changing things.
I do not know much about the 900’s but to me they look more “crafty” in hiding things. Like screws and hoses than they did on my 240s.
I never cared for the 700 series either and it didn’t surprise they had a short life trying to change up models.
The 900 series body was a definite improvement though I have never even driven one along with any turbo.
You could say I’m stuck in a rut of liking to be kissed. Keep It Simple Stupid is a type of engineering guide line.

The electronics use signals more than higher voltages or high current flows.
A electric motors has initial high current draws to initiate movements.
They have to have the voltage to deliver the currents. A Hand and Glove thing.
The IAC is a slight rotational or limited turning motor with a spring return.
The return spring was an upgrade due to sticking issues.
The commutator wears a lot differently to cause sticking.
In saying it can be a little quirky with age.

Why the change out kept it the same cannot be explained.
Nor can I guess why jumping to the ECU was a next choice?
In so, who’s to say is not an absolutely definitively answer to the problem. But if it worked, so far?

Still it’s about more about how air getting into that engine!
A Dirty Throttle body sure explains more air
Sometimes these gremlins will ride a Ferris Wheel for fun?

Phil


To Volvo from Heck.
If you have hung on to a dozen or so ECUs for the 240s what does that say for the reliability of ECUs.
I have a stashed one ECUs each for my mid eighties cars and nineties cars. I would have to hunt them up and review all numbers of those. Never thought about the 1978 being different but it still works.
When the EGRs creeped onto the scene in the nineties they became another source for an air leak.

I tried to not get a wrong colored label that came on the very early ECUs.
The way you have collected is better than JY prices.
Probably not possible to stash one as finding one left in a 240 junker commercially.

Dave, I assume you got yours from several cars that you junked over your years as a mechanic.
I can see why you speculated and hoped to make it worth your while.
I’m not sure if I would need one but you are making up a tantalizing offer for any conservative eclectic like me.
I do not know if I have all my cars covered so you might want to display an inventory to sort through to promote interest without “per se” advertising.
An informative of car years model and numbers can be thought about in several ways, but being marketing.

Just a thought,

Phil

Try cleaning the contact strip first and give it a try. Scrap metal places pay for electronic equipment. I don't know what they pay but considering that I've had a dozen or so 240 computers for sale for years, asking $5 each, and haven't sold a single one - I'll take whatever they give. They all came from running cars if anyone is interested. - Dave