So, after putting the A/C-delete belt on to take my POS A/C compressor out of play, everything works great:
- No frightening rattle / clanging from the engine bay
- Idles smooth
- Sounds like a brand new engine. Which it should, since I've only put about 8k miles on it since I rebuilt the thing.
- CEL for "System too lean bank 1," which has been haunting me for a year, is finally gone. Very weird!
Note that I also replaced the oil dipstick tube when I changed the belt. I had the one from the Malibu this engine came from, but it's a different length and shape than the Solstice tube, and wouldn't bolt to the intake manifold correctly. shrug A side effect is that the dipstick doesn't seat firmly in the tube now - must be different diameters - so I'm waiting on a replacement dipstick to arrive.
(Tangent: could a loose-fitting dipstick cause a vacuum leak?)
The Other Shoe When I first start the car, everything runs very, very smoothly. Sounds great, lots of power, etc. When it gets up to temp, however, the engine starts getting the hiccups. Somewhat at idle, but very noticeable when accelerating. If I keep throttle below ~20%, it runs well enough to drive, but is very disconcerting. If I let the car sit overnight, everything is exactly the same the next day (runs great until it warms up).
Suggestions? There's also a weird issue with the coolant temp sensor. It occasionally reads "---". I've ordered a new one, will put it on this weekend.
Earlier today, I decided to drive it lunch. After lunch, I made it about 50 feet before it went into "Reduced Power" mode. I pulled the negative battery cable for a few seconds, then everything was fine for the subsequent short drive home.
That's happened before, though I forgot to mention it.
Update the 2nd
Title updated to reflect new information
So, it's not directly related to the engine temperature or closed-loop status.
I've been driving the wife's car for the last few days. A little while ago, I started up my car, and it ran fine - until I hit the gas (in neutral). It revved fine, but when I let it go back to idle, it started trying to die, then revved up, went back down, sounded like it was having a seizure. The "reduced engine power" light came on instantly. I shut it down as I don't have time to look at it right now.
I'm wondering if there is a problem with the throttle body. There's no CEL so I assume the TPS is fine. I was running a compression test a few weeks ago and propped the butterfly valve open with a wrench, may have messed something up in the process. I checked the harness connector to the throttle body and it looks fine, will pull the intake hose off when I get some time and look for binding, etc. There is a significant amount of oil in the intake on the turbo side (near where the hose connecting the intake to the valve cover goes), maybe the butterfly valve is getting gummed up or something.
The weirdest part is that this just started immediately after I replaced the engine oil dipstick tube and put the A/C-delete belt on. (The only other thing driven by that belt is the alternator, which now has a dedicated belt.)