My '99 neon (dohc 5speed 60K) just now threw a p0304 (misfire code)on cylinders 1 and 2. The idle has been slightly rough for the last couple of weeks but mainly there is just excesssive vibration at idle and a very slight knock (idle only)when cold. I replaced the front and drivers side motor mounts (this is before it threw a code) thinking that was the cause of the vibration. The front motor mount was broken but vibration did not improve and now of course I'm getting the code. Ignition wires (NGK #RC-ME83) and spark plugs (stanadard NGK) have been replaced in that last 1,000 miles. The car only gets driven a few hundred miles a month.The idle is the onlyissue. When driving the caris smooth as silk through the rev range and hasn't missed once.

Any thoughts on where I should start. Is the coil pack starting to go bad?

Thanks!!

 

I would pull the plugs to check there condition and gap. Then if you dont find it there start your car up and let it idle like it has been and start pulling plug wires, if it dies or gets worse you know that plug wire is good if you pull it and it stays the same its the plug wire if they all check out I would try the coil pack just work it backwards. If all three of those things dont fix the problem. I would then start in on the injectors put a screwdriver tip up to the body of the injector and put the handle to your ear, you should hear a steady ticking noise, if it is off rythem or you just dont hear anything then its a bad injector. Try this and see what happens...

 

Also inspect the coil pack for cracks and check the leads on the coil pack as well.

 

It's definitely not the coil pack. I replaced it yesterday and cleared the codes and then this morning it threw the same misfire code. I had pulled the #1 spark plug yesterday and both the gap and overall conditionlooked just fine. The wires all look good also.

I'll see how the the injectors sound tomorrow.
Idrove it pretty hard today just to see ifit would act up other than at idle and even though it sounds okay it's definitely not where it should be power wise.

I'll reply back after I check the injectors.

 

Next step would be to check the injectors and then possibly the fuel rail for trash in it.

 

P0304 is cylinder 4 (0300 is random/multiple, 301 is #1, 302 #2, 303 is#3 and 304 is #4). Just because plugs and wires are new does not mean they're OK; check them. Make sure rodents haven't chewed on the wire. Inspect the boot for carbon tracking and make sure the spark plug insulator is not cracked and that it is gapped correctly. Inspect the coil pack for a crack or carbon tracking around the #4 tower. If that stuff looks good, check compression. If compression is solid, make sure the #4 injector is firing and not leaking. If all those things are fine, put a new coil pack on it.

Edit; Sorry, missed the part about already replacing the coil pack. But you've still been chasing the wrong hole.

 

Thanks for the correction on the trouble code sixtysixdeuce. I just checked the fuel injectors and they all sound normal. There waswhat sounded like hissing air near the right side of the fuel rail. Don't know if that's normal or not. I'll pull all the plugs tomorrow since I haven't yet looked at the #4 plug.

 

Right side as in when your facing it? Because that would suggest to me a vacuum leak near the #4, which can certainly be the culprit of your misfire. Spray some carb cleaner in the viscinity and see if the miss gets worse or engine struggles. If so, you've found the problem.

 

I just messed with it a little more. As much as I can tell the hissing (vacuum leak) sounds like it's coming from the #4 injector itself. The vacuum lines in that vicinity look okay. I sprayed a littleCRC electrnoics cleaner (didn't have carb cleaner lol) on the injector body and it did start to stumble. So what do you think just a bad oring on the injector?

 

Just an update: Finally found the problem. I replaced all the fuel injector orings and vacuum leak/noise was still right around fuel injector #4. Upon further inspection I discovered that the actual problem was the intake seal. It's not sealing on the upperright side. I just put some RTV sealant on the leak and am hoping that will at least be a temp fix before I have to replace the intake gasket.