Adding 1-2 tablespoons of MMO to each cylinder will not harm anything and if a ring is stuck, it just might free it up.

To avoid mess, use a drinking straw and dip it into the bottle about 2 inches deep, put your finger over the end and then insert the straw into the spark plug hole, remove finger and let the oil run into the cylinder. Do this once for each cylinder. Let sit overnight, the MMO will drain through the rings and into the sump and you need do nothing except insert the plugs and start the car.

Changing the Tbelt should not have changed anything, but you could still check the timing marks and verify that the tensioner didn't mess anything up.

If the ECT sensor was original to the car, it was time to change it out anyway.

You might want to take an old tire pressure gauge and check the fuel pressure at the end of the fuel rail, engine warm and idling. I get extra pressure gauges at Discount Tire for free!
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