Well, that was easy.

I was able to jack up my car, remover the valve, and install my used back up valve and be completely done within 25 minutes. I took the car for a short test drive last night, and then let it sit for 13 hours overnight.

The car started up perfectly this afternoon, and although she hesitated just a little bit when pulling away from the stop sign, it was a 100% improvement over the previous two days.

I will let ya'll know how she performs the next few days.
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If it needs to be maintained, repaired or replaced on a 1990 240, I've probably done it. '90 240DL, 291K looking forward to 300K badge (or sticker??). >>You haven't really worked on a car until you draw blood<< :-}