I have a 98 accord 4cyl vtec. Ive been working on it a bunch lately because of stalling/idle issues. I had a mechanic replace a oil pressure switch this last week and everything seems to be fine since then. Although the issue I was having was pretty random and unpredictable.

Last night the check engine light came on. It was p0304 and p1399. Cylinder 4 misfire and random cyliner misfire. I never felt the car sputter or anything. It may be idling a little bit hard, but it never hesitated or stalled.

1. Is it common for misfire codes to pop up without "feeling" the misfiring?
2. Any good ideas what to attack? Already done plugs/wires/iacv/egr/cleaned throttle body.

 

Have you checked/replaced the distributor yet?
Misfires on a certain or all cylinders are usually an ignition issue.

 

Can you take a very good picture of your spark plugs and post it ? Make sure to mark which plugs go to which cylinders. I think in this situation the spark plugs might be key.