I'm hoping for some comments and suggestions on two issues. One is engine, one is drivetrain. I'll post one here and do another post for the other. My '90 has 225,000. I got it at 190,000. It ran ok and got about 22 mpg and slowly went downhill. Some rough running, some hard starting, some hesitation, and about 17-18 mpg. Compression is good. I found this board (yes!) and as I used to service VW a long time ago, I used to be able to make type 3's run when they were one of the first, maybe the first, production car with FI, I thought I had some clue about things. But the days of points and rebuilding carbs are gone. I took it to a Volvo mech to have it analyzed and he said the AMM was going out, the intank pump doesn't work, and a couple of other things like Bosch platinum are not good for this car. I had gotten some and felt an immediate increase in power, so ??
My cash situation has been on the low side so I wanted to do as much as I could myself. I read the FAQ and did the flame trap (was blocked) and then cleaned the throttle body, hoses etc. When I did that I saw that the throttle linkage wasn't where it should have been so I carefully reset it. I had an immediate and dramatic improvement. Really a major difference. Thanks to all who have contributed to the FAQ. All this made me doubt the info I had paid for, as a former mech I saw many issues around people being misinformed by a tech to make the garage some money, and the throttle adjustment was so obviously off and easy to see by anyone who is familiar, so I haven't changed the pump or the AMM.
So now it runs much better. Still has some issues though. There's a knock sometimes (midgrade Cal gas) and there's more power sometimes and it's not a regular thing. On a recent trip I noticed an occasional momentary miss so small I thought I could be imagining it, but it recurred several times. Also the idle is sometimes so smooth you can't tell the car is running, and sometimes there's a little bit of vibration. I'm leaning towards this theory, that the intank pump is working sometimes and that makes it have sufficient power, and when it's not, or not as much as it should, fuel delivery is low so it knocks. Does this make sense? I haven't tried putting an ohmmeter on the AMM yet to see how it reads, not sure where/how to put the leads exactly.