Runs great sometimes and terrible others. Help!

[RP3]

My 94 6cyl automatic will start and run great sometimes, and start and backfire and run terrible others. However it starts, it will continue to run like that until you shut it off. No rhyme or reason to wich one you get when you start it. My mechanic has been working at it, but still no luck. Any help would be much appreciated. Thanks

 

[Gilaguy23]

Try to pull the codes to start. Bad ignition switch making intermittent contact perhaps?? Just a thought as my 91's can can act up dependent on how I turn the key.

 

[cas]

My rule #1 on any modern* car, when there's running issues, the first thing I check are the grounds.

Next time it's running bad, leave it running and hook up a jumper cable, both camps on one end to the negative terminal. The other side to the engine and frame.

*(meaning anything fuel injected, anything with a computer, anything that don't have points lol)

 

[RP3]

My rule #1 on any modern* car, when there's running issues, the first thing I check are the grounds.

Next time it's running bad, leave it running and hook up a jumper cable, both camps on one end to the negative terminal. The other side to the engine and frame.

*(meaning anything fuel injected, anything with a computer, anything that don't have points lol)

Thank you. Will give it a try. Just weird how it’s one or the other when you start it. Nothing seems to change it .