Hello tinypanzer,

I agree with you that the thermostat is probably not causing the loss of economy as I am able to check and set the duty cycle which, as I understand, means the car is getting into closed-loop mode. The engine used to run at about horizontal on the gauge (whatever temp that is), but now sticks to around the 80 degree marker and gets there quickly from a cold start after which it idles relatively smoothly.

There currently isn't any visible smoke coming out the tailpipe, but I will try to see if I can see any at night with a flashlight. I also rotated the coolant temp sensor connector 90 degrees per your tip, though the two elements in there seemed to have matching values when checked with a multimeter.

No fuel odor around the fuel filter/pump area. The plugs installed by the mechanic on a previous tune-up were NGK TR5's, and I've swapped them back to H9DC0's picked up from the dealer. The TR5's looked ok, didn't seem to show any rich mixture. The cap and rotor appear to be ok, though I swapped them this afternoon while I had the cap off with my fresh backup set just to be safe.

I don't know if a leaking injector can affect start up, but the engine starts up on first crank almost immediately, hot or cold. I will leave the car parked for a couple of days to check again for fuel pooling under the air flap. There were no signs the last time I left it overnight, but maybe it evaporated? I will also check the plunger while I'm there.

I spoke with my mechanic again today and he said that the only other thing he could do besides replacing the thermostat was a tune-up, which doesn't sound right to me at all. I'm really hoping that it's not the fuel distributor - that part is quite a few pennies!