I wanted to see if anyone may be able to diagnose the problem I am
having with my 2001 Elantra. Sometimes when I accelerate, typically
after I first start the car, the car will seem to not be able to shift
out of 3rd gear(it's an automatic), then the car kinda jolts and the
engine light comes on. After this point the car accelerates slowly.
When the vehicle is shut off for a a short time, maybe an hour or
less,  the car is fine. Usually the car seems to drive like nothing is
wrong this just happens intermittedly. Seems to occur also when I
drive then turn it off for a short time then restart the car and drive
again. When I take it into the shop and tell them about it they can't
tell me what the problem is, or replicate the problem, and without the
engine light being on they can't run the error codes.

Also, when I first turn on the car after it has been sitting around
awhile it idles at about 1500rpm when it should be at 500rpm. It will
go down to that after I either shift into drive or reverse.

Another related problem I had was that about a year ago when I started
the car the engine light would be on right from when I started the car
producing the same issues with acceleration, but again the shop could
not diagnose this or replicate this. This does not happen any more.

I'd appreciate any suggestions on what could be causing this problem.
Thanks.