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.

[Marsstar505]

Try running some seafoam through the vacuum booster line to clean the intake of carbon the rough idle is probably build up in the egr. Also change the plugs and wires with oem recommended plugs and factory wires. And change the distributor cap and rotor. And on these cars the ignition coil is part of the distributor.

[Box]

What's the idle speed? It should be around 850 once warmed up. The ignition coil is on the distributor cap. If the plugs are worn they need to be replaced anyway.

[freeriders98]

Awesome thanks. All good info. So is it the consensus that OEM plugs and wires are best? I know it seems every vehicle tends to like different stuff. What are the OEM plugs and wires.

And just for clarification, the ignition coil is on the disti cap or the actual disti?

[HaysoosKreesto]

I'd also say trying cleaning the throttle body/ Idle air control valve. I was thinking about outright replacing mine because of problems starting, but once it's warm it's fine.

It's easy and fairly cheap. Honestly tho if it's throwing a misfire code, I'd think about changing the distributor cap, the cap and rotor is not Toyota's strong point.

http://www.obd-codes.com/p0302

[freeriders98]

What distributor cap is recommended?

[HaysoosKreesto]

I like bosch products, but if you are unsure of what oem product to buy I'm almost certain you can get something from the local Toyota Dealership

[Box]

As far as plugs and wires go NGK wires with NGK platinum plugs will be good. The coil is on the cap's side if memory serves correctly. Cap and rotor of any name brand should be good. RockAuto probably has the best prices for everything, and can even search Google for a 5% coupon to save even more. Should be able to get everything for under $50 or so from RockAuto. Wouldn't bother with cleaning the IACV if the idle speeds are correct.

[Bitter]

Check compression before you just go throwing money at it, if you have a mechanical issue then plugs and wires and caps won't fix it. Check inside the cap for fouling and carbon tracking, check the wires for cuts or rubbed through spots, check the ceramic of the plug for carbon tracking as well.

[freeriders98]

I haven't checked compression on it yet, but it runs great and isn't miss firing or down on power from what I can feel at all. Not ruling it out, but from the way it runs I think it is more along the lines of the ignition system.

So on the distributor cap. I looked at the box store websites for a distributor cap, and you can get Bosch, AC Delco, etc all for $15-20. It seems hard for me to believe that price would get me a cap and a coil...Sorry for some of the stupid questions. I am working 12 hr shifts right now with 3 hours of driving. So I haven't even had time to pop the hood and look. But i'm trying to order parts so I can get it knocked out on my days off.

Again thanks for all your input. I am a dirt bike and 4x4 guy. So this motor and car I am not to familiar with.

[VavAlephVav]

A lot of people just haven't seen what good deals they can get on Rockauto, it's like direct wholesale prices sometimes I can even buy the factory brand like Aisin and Denso for half the price you'd pay at Toyota.
I while back I bought some Ceramic pads that said "private label package" for $17 and when I got them they were in a NAPA box and where the set NAPA sells for $70

[Bitter]

If it's running properly otherwise it's probably not a compression issue. It could be as simple as an injector o-ring leaking vacuum on that one cylinder even.

[freeriders98]

I've got a Wells brand Cap and rotor coming, along with a new set of plugs. I've got 2 days left of work before 4 days off. So I'll take a look at the injector oring for damage and run some seafoam through the brake booster vacuum line.

Thanks again for the help and direction.

[Marsstar505]

The ignition coil is on the distributor side it the back plug on the distributor. As for plugs I know they're Ngk platinums but I'm not sure more than that autozone can tell you. I personally say get the wires at toyota every toyota I've had I first got wires from parts store and they are terrible and ark through the wire causing a miss fire.

[Box]

Yep, RockAuto is where I buy my parts some 95% of the time. Sometimes when buying only one part the shipping will be silly and it's better to buy off eBay or Amazon. Whatever they use for determining shipping is really weird at times, as sometimes a more expensive part will end up less because of shipping. I guess it all has to do with which warehouse it's coming from. Anyway, I and my family constantly do business with them and they're the best. If you ever have an issue they generally resolve it within 24 hours. One time they forgot one of my parts, so I got on the site and let them know and they shipped it for no cost with no questions asked. Most other places they'd have you jumping through hoops and tearing your hair out.

Anyhow, ditto on doubting it's a compression issue. If it were a carbureted vehicle I'd point at A/F mixture, but being fuel injected that shouldn't be an issue.

This post has been edited by Box: Dec 26, 2014 - 5:03 PM

[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.

[Box]

Only thing would be careful with the carb cleaner around the injectors, as it will make the o-rings swell and deteriorate. That or go ahead and replace the the o-rings and while the injectors are out have them flushed out. It's not too terribly hard to get down to the fuel rail on the Celica.

[Bitter]

Nah, carb cleaner won't hurt the injector o-rings. They're fuel rated rubber so a little dousing won't harm them.

[freeriders98]

Ok. So new cap and rotor are on. Drove for about 70 miles then the light came back on. The Cap and Rotor I took off looked to be good. There was a tiny bit of oil, but nothing really on the cap itself.