I feel I have solved the problem approx. 90%. The last, and most successful, thing I have done was to replace the ptc nipple. It has original Volvo part number 1357352. I will not be near the car until 4-5 days, but I think I remember that it is on the hose between crankcase ventilation and hose between turbo and air flow meter. It cost no more than approx. $ 30 at Volvo dealer. The reason I changed it was that I suddenly discovered an electrical contact on it to become curious if it could have an effect on idle. I compared the ohm values of the old and new nipples, and there was a marked difference. As mentioned, I only feel 90% successful, this is because if I start the engine and drive immediately, idling is 100% normal, but if I wait about 20 seconds to drive, after starting, idling can return to abnormal state again. The next thing I plan to do is replace the air flow meter. I did this at the beginning of the troubleshooting, without success, but that was before I was aware of the learning function on the LH 2.4 Jetronic, so I suspect that I did not give it enough time to adjust to the new air flow meter. Regardless: The new ptc nipple I put on had, in my experience, definitely an impact on the problem. I will try to keep in mind to update on this forum when I see the effect of the replacement of the air flow meter.