Q: Trouble starting unless I prime the fuel pump, turn off key and then prime again and start it.

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Trouble starting engine, I have to switch to "on" wait a few seconds, then back to "on" then finally turn the key to start engine. If I try to start normally, it would hold the idle and dies after a couple seconds or doesn't crank over at all. Possible fuel pressure regulator or more serious?

My car has 180000 miles.
My car has an automatic transmission.

The most common cause of the fuel system not holding pressure up to the injectors is the fuel pump inside the fuel tank. The fuel pump has a check valve built into it that is supposed to keep pressure to the injection system when you shut down and vehicle sits. If the pressure drops then the pump has to prime the system to bring the pressure high enough to start and run the engine. You should have a mechanic like one from YourMechanic come and test the hard start to see if the pump is bad or there is another issue like a pressure regulator not holding pressure. The pump is most common and should be replaced with a new fuel filter at the same time.

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