Thanks for the link, Klaus- lots of good information. I removed, cleaned and tested the solenoid and it appears to be working. I reinstalled it today with a new gasket, but no change in the performance. I did get a new code after starting it- P0343 "Camshaft Position Sensor A - Bank 1 Circuit High Input".

I'm still wondering if the belt jumped a tooth on the crank. I removed the belt cover while working on the suspension to look for an oil leak. I had some difficulty getting the cover back into position before cranking the engine, but it seemed to be right. Maybe the cover was in contact with the belt or tensioner when I started it. Seems unlikely, but that is the only thing I did that was remotely associated with this problem. If that's not it, I don't know what to do besides start replacing some expensive parts.