2002 mazda 626 2L 4 speed.

Runs great in summer with no codes, no issues.

Last winter codes came on (p1516, p0303), car missed, ran rough, idled badly, sometimes stalling. The poor permformence increased the colder the outside temp got. If left idling for a while the cel would blink.

Last spring codes disappeared and stayed off and car ran great

This winter when it got cold poor perfomence and codes came back (p1516, p0303). Car almost always starts on first try, in winter maybe second or third try. In cold weather, same condtions prevail even when the car engine temp warms.

I changed plugs. I think the coils are good (not many miles). Inpsected air filter, PCV, coolent temp sensor, fliuid levels and thermosat and all appear to look good or appeared to work properly. Inspected and cleaned MAF, it also appeared to be good. I think I have low compression in one cyliner, but still runs great and ildes smothly in summer. Codes now are P0303 and P0172. I suspected a bad coolent temp sensor, but after a cold start the high idling drops to normal rpm when it gets to operating temp, so I have ruled that out.

Can anyone provide any thoughts what the issues might be. Thanks in advance