stalled at idle in drive

My girlfriends 2001 se stalled at a light w/o the AC on. It sputtered and stalled which leads me to believe it's not an electrical problem. Should new plugs and a fuel injection cleaning take care of it? Air filter is clean. The gas was a bit less than 1/4 but the gas light wasn't on yet so i don't think that was the problem. I put a new fuel filter in at 48,000 miles. The car has 54,000 now.
For the plugs: what's the trick to those I can't even find them. Are they covered up by something?
Its the 4-cylinder by the way. Thanks.

The cover on the top of the engine comes off and there are the plugs