Hello,

I changed my o2 sensor this helped the missing and hesitation problem, RUNS great UNTIL. Now after turning off the engine and restarting it is back to the same problem??? 2003 2.5 outback sport

Have you checked for codes?

yes none come back

There are several possibilities but if faced with the same problem I'd change the coolant temp sensor that tells the ECU how hot the engine is. It's fairly cheap and easy to start with. I think you could be having any number of electronic problems but the temp sensor often throws no code. I'm sure some other folks may have other ideas from thier experience.

I will replace the coolant temp sensor! Thanks. FYI new plugs and wires fuel filter air filter. For some reason isopropyl helps if it is acting up. I have had this problem for several tanks of gas the last were 91 octane. I tried seafoam in gas tank it was a temp fix as isopropyl is. Hopefully this info may help.