Hi,
Here are some of the symptoms. I think they are closely related.
1) Elantra (2001, 90k) misfires and noticeable when the engine is started.
(Spark plug changed, not spark wires)
2) When the car runs for first mile during a day, it dies at the first few stops.
After about a mile or two run it does not die.
If i give more gas when it has died it gets of. However if more gas is not given it will not go and die again and I again need to restart.
3) Can see a reduction in fuel efficiency.
4) Can a bad fuel filter cause both these problems simulaneously?
Or there can be more issues?.

 

Change the fuel filter. Scan for trouble codes.

 

Engine check light is not on..

 

Ok, well replace the fuel filter, and if that doesn't help, do a fuel pressure check. Sometimes there will be codes present, but no trouble code light. If you can take it to Autozone, tell them you have a check engine light lit, and they will do a free code scan.