codes?
might be O2 (but no code?) also if it immediately stalls out seemingly random, then sometimes amazingly cranks up... check the wire going down to the CKP crank position sensor, it lays near the firewall side exhaust manifold and is easily burned to a crisp, shorting out. when it unshorts it will start up again. it's a 2 wire, runs near the egr, and down the back side (firewall side) of the engine.. the crank position sensor is below the #4 cylinder and in attempting to change it the mechanic could have accidently moved it right onto the exhaust manifold. I can't remember how i originally changed mine.. i think i could spot it from underneath the car, but changed it by feel from the topside.
I had mine burn up a few years ago and replacing the wire fixed it right up! Runs by the throttle body, then along the exhaust manifold (STUPID DESIGN) and down to the block where you cant see it.
And by the way, this is NOT the crank sensor near the front harmonic balancer... there are two. The one i am talkign about is the 7X.
in the attached pic, the red line is the general path you will find the wire.. it is inside a black plastic loom... probably melted.
most mechanics will probably fail to identify this as you really have to look for it - im surprised I identified my problem so easily - unless they have seen this problem before.