I've had my engine check light come on a few times now.. since it's been cold out it's been on steady.

It Idles rough
When I drive and then push in the clutch between 1000 and 2000rpm the engine will rev to 2500rpm and stay steay for a few seconds and then drop to 1500rpm and then idle at around 750rpm.
If I'm over 3000rpm and push in the clutch, the engine will stay steady at whatever rpm i'm at for a few seconds and then go down to 1500rpm then to 750rpm after another second or so..
If I haven't put it in gear and driven and just rev the engine it drops down quickly..

only happens when I drive for a bit (say 10-20 meters or so and further...)

Code is P0303 - Misfire #3, so far i've changed the plugs and wires

please help

This post has been edited by mike.p: Nov 13 2009, 08:06 AM

Dear P0303, I own a 2002 Elantra and have experienced the same problem! It's sounds like the intake manifold gasket has started to leak-allowing air to pass through. If you happen to have throttle body cleaner (which you can get at any auto parts store in a aeresol can) spray onto the intake manifold gasket housing which located underneath the throttle body. If you notice an immediate change in engine idle, you have found your problem. The gasket alone should be under $20.

Hope this helps,

KIDWATT

Thanks!... I just changed the intake manifold gasket this weekend and it was the problem... there was a whole section missing right over the #3 cylinder.