Today I replaced the PCM (powertrain control module) with one I had bought a while back on Ebay, and took the car on a brief test drive. It ran better, and the transmission shifted better than with the old PCM. And there was no SES light. So I'm declaring the engine done for now, and it's time to think about body work and paint. There's a bad spot on one of the aftermarket side scoops, that looks like someone just slapped a little resin or body putty on to "fix" it, with no sanding or shaping, and the dew wipes are completely rotten. And there's a few places where paint layers are flaking off, but I think the paint shop can handle those. I'm not sure when I can take care of these things, but hopefully I'll have it looking good next spring.