I realize this is going against all current Netiquette ;-) but I thought I'd tell you what it was. It was the oxygen sensor
*relay*.At least after about 150 miles since it was changed, and the car running just great, I am willing to take a gamble and say that they finally got it right this time.
I /tried/ to figure out how much my mpg has improved, but I've used calculators since the mid-70's, and I'm 53 and have been getting stupider (specifically speaking, losing brain cells at an increasing rate) since about when I turned 30 (this is a scientific fact for all humans, no matter how much you may not like it).
So I am not at all sure whether my previous calculations (of about 15 mpg) were /anywhere/ near correct, but it would appear I am now getting between 20 and 25 mpg. The 20% margin is because of the differences between US and imperial miles and gallons, and the fact the US appears to have dry and liquid gallons and the UK just "gallons". Is pudding liquid or dry (*after* it's made)?
20-25 mpg is just fine with me. I drive the car less than ever - like once every 7-10 days. (How you guys manage with those insane units of measure is beyond me. I will /never/ understand why anyone would say something is XX Guineas instead of XX £ unless they just enjoy being snotty.)The third Temic coil is OK so far, as well (for those of you with a good memory).
Again, thanks to all who tried to help. I am more than ever convinced the whole car repair thing is basically hopeless. How many of you even /knew/ there was such a thing as an oxygen sensor relay? I sure as hell did not, and no one I spoke to /here/ or wrote to "here" mentioned it either. And I certainly will not be surprised if the car doesn't start the next time.
Cheers.