New guy needs help!!! P0302 misfire Options

[freeriders98]

So I just picked up a 96 GT. Guy I got it from said it had a rough idle and check engine light would come on occasionally. Had a rough idle, but CEL was off when I test drove it. Of course it showed up the next morning...

So here is what I know now. CEL is throwing a P0302 code. It only happens if I let it idle for a bit, like warming it up on a cold morning. Before I drove it home after buying it (4hr drive) I cleared the light it and it never came on.

At idle it is rough, but as soon as it comes about 1000rpm it smooths right out and runs really nice.

I checked the plugs today, all looked good. It has midgrade NGK's in it.

I've been looking for some pointers for a couple days now, and have searched on here.

Most reference a coil/plug set-up. So does my Celica have just a standard single ignition coil mounted on the fire wall?

How likely is it that plug wires are my issue? The ones on it are tiny and look to be a generic set. Would a set of better insulated NGK wires help? I know that wires can get interference and cause some firing issues if not well enough insulated.

And help or input would be great. I'd like to at least narrow it down to 1 or 2 things before I start throwing money at it.

[Bitter]

No, it could still be a A/F issue if there's a vacuum leak at ONLY that cylinder. Highest vacuum is at idle so you'd see it acting up more then than say when driving or accelerating. A bad injector O-ring or a bad intake manifold gasket can cause a leak at only one cylinder. Spray some carb cleaner around those areas to check for issues, if the idle changes repeatedly when spraying one area then you've found something. Worst case you end up washing a bunch of nasty grime off with some carb cleaner and get a little head rush from the fumes.

[freeriders98]

No, it could still be a A/F issue if there's a vacuum leak at ONLY that cylinder. Highest vacuum is at idle so you'd see it acting up more then than say when driving or accelerating. A bad injector O-ring or a bad intake manifold gasket can cause a leak at only one cylinder. Spray some carb cleaner around those areas to check for issues, if the idle changes repeatedly when spraying one area then you've found something. Worst case you end up washing a bunch of nasty grime off with some carb cleaner and get a little head rush from the fumes.

Good info. I'll give that a shot. Let's hope its not the intake manifold... Replacing one of those on my 5.7 vortex suburban this stretch of days off...notnlooking forward to that at all.