Distributors initially had weights and return springs in them that from centrifugal force advanced the timing with higher rpm. - that is controlled electronically beginning in 1975? for Volvo.

The idle mixture screw - and using an exhaust gas analyzer attempting to adjust the idle mixture - I found most of those (adjusters) did nothing when the AMMs got old. And even if the mixture changed, it made very little difference to the way the car ran. In theory once the O2 sensor goes into closed loop - that takes over the mixture control all the time.

Later Volvos (88-89+) use an air mass meter without any adjustments.

 

on the LH2.2 cars (85-88) the idle air screw is on the throttle body, the screw on the MAF/AMM is for trimming lambda. on LH2.4 (89+), both were done away with.

 

i cleaned the IAC today and the high idle persists.

regarding disconnecting the ICU harness - it seems pretty damn stuck on there. I'm really afraid of breaking it and having the 240 go down. but I guess the technique is just to pull it straight off? should I use any tools or sprays to help loosen it?

 

high idle persists across all gears. car will accelerate from stop to 20-25mph without giving it any throttle. it does this on it's own. not sure what that means.

still haven't gotten the ICU connector off. really trying to be gentle, though.

 

maybe the throttle is sticking open?

 

messing around now, the throttle plate wasn't binding as far as I could tell. I cleaned the idle bypass chambers - no effect. now I have the throttle rod disconnected from the pulley and TPS loose - and the car still idles high. i can't seem to get it to the proper idle no matter how I adjust the throttle plate. mind, I'm going by feel as I don't have a tach and for whatever reason, my meter is erratic when trying to read Hz off the coil.

what bothers me, though, is that this condition developed randomly. I had the TPS and throttle correctly adjusted and the idle set correctly in June. then I replaced the IAC. then the high idle started. so it would seem like the IAC is the culprit - and yet it appears to function normally, as I've observed it close and open grounding the test terminal and have cleaned it

this car is just determined to crush my spirit! wow. what a drag. two gremlins.

 

well I got the ICU harness off and took the box out - and I can't see any obvious soldering faults thru the gel. the harness connector is pretty gunky and so is in the ICU terminal, but I'm going to clean them up and put fresh dielectric grease in. additionally, I can see that I have sleeves on pins 3, 5 and 9 on the ICU pins - the ones that go to the distributor, as I understand. so for the dying/no start issue, I'm going to look deeper into fuel system. maybe an intermittent main pump or overheating main pump.