a "Garage" might screw up the car even worse.
Well - if you're a DIY mechanic then I'd have to ask just what you expect
anyone to be able to say in answer to the original post? OK - try this on
for size.
1) Check your gas cap.
2) If it's not on tight, then read the owner's manual to see how to
properly
install the gas cap. Exercise caution as afterall, you are working in the
vicinity of gasoline which is highly combustible.
3) If the gas cap is on tight, then take your car to a garage for further
evaluation.
Okay,
why would a gas cap, not properly screwed in cause a "check engine" light to
come on? Call me silly (no, please don't call me silly

BUT, I've never heard of that. Fuel pressure sensor somewhere that detects
this? would a bad cap do it?
Gas=petrol
Petrol=gas
a "Garage" might screw up the car even worse" - highly doubtful.
Not around my neighborhood..

)
Perhaps you mean "garage" as in a "Authorized Dealer"
the last garage I used, was for a cracked main pulley (harmonic balancer)
a week after that, I noticed belt slippage from the alternator, later I
found out they never installed the nut on the bottom bolt!
I re-inserted the bolt all the way in, and installed another nut myself.
I will eventually visit the shop (garage) that did this crappy service, and
give them a piece of my mind. (just a small piece, since ive lost most of it
anyway

)
THANK YOU MIKE
cheers
Dave