2002 Mazda 626 2L 4 speed Winter Performance Issues.
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 performance 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 performance and codes came back (p1516, p0303). Car almost always starts on first try, in winter maybe second or third try. In cold weather, same conditions prevail even when the car engine temp warms.
I changed plugs. I think the coils are good (not many miles). Inspected air filter, PCV, coolant temp sensor, fluid levels and thermostat 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 cylinder, but still runs great and idles smoothly in summer. Codes now are P0303 and P0172. I suspected a bad coolant 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.
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