Hi,

It’s interesting that you moved both the TPS and the IAC over from the 1991, to the daughters car and nothing changed?
I do not think this is a coolant temperature issue if it runs fine otherwise.
You can that at the ECU also. I think it’s pin 21 or something like that?

I looked up a reference chart, I found some time ago, that shows outs of changes with the ECU’s just after the 1989 year.
Look here and see.
http://www.nuceng.ca/bill/volvo/database/ecu.htm

It makes a comment about the 561 in boxes below that move up in years. So just thinking you might be on to an issue that occurs with the 561 from time to time.

Like Pageda says, the TPS either work or they don’t, if they are set right. An ohmmeter must show it operating with the throttle closed and then open. We don’t care which way it goes, just as long as it changes an state, to its opposite reading. Same for the wide open throttle position.
It should be telling the ECU to go from idle to Powering up mode or Wide Open Throttle mode.
The idle is guided by rpms inside the EZK system.

The TPS gives the ECU a heads up that the, driver, is changing air flow quickly! The ECU is fast to shift things but there are other things involved, that that are not going to report it, too it, in time.
That’s why there is the TPS to give it the extra heads up that shifts the programs to drive on.
As he says the TPS has to be set on the hairs edge of the throttle plate wiggling open from being absolutely shut down.
This is where the stop screw gets over used incorrectly. It’s not an idle screw but a STOP screw to prevent the return spring from possibly over jamming the throttle plate closed in the bore,
in case of a fall from WOT.

If you are not having the idle “jump up” upon starting, with you foot completely off the gas pedal, it’s not doing like it’s supposed too!
The IAC has to have complete control.
The TB has to be set within its range and not higher! Apparently you are low enough that you need an operating IAC or a signal to the ECU or it must need to respond back to the IAC.

I’m afraid that you are onto “A” harness issue to the TPS or the ECU has gone consistently flaky!
You can read up on the “intermittent stalling” issue here on the same year but 700’s.

https://www.volvoclub.org.uk/faq/EngineFIComputer.html#Intermittent_Stalling_Bad_ECU

You will have to scroll around a little but it’s interesting!

Good luck
I hope this helps!

Edit: I should look before I post! Art was here, just like Mighty Mouse! (:) he saves the day!

Phil