98 Camry v6 230k P0302 P0304 Rough idle, hesitation

[RKE4]

I've got a 98 camry v6 that started with a rough idle and stuttering/hesitating about 10 days ago. The hesitation/stuttering seems to stop if I take my foot off the gas. There are times when it seems to run fine. At first, no CEL, but it has come on a couple of times, giving P0300, P0302, and P0304. Since it started, I have have valve cover gaskets replaced, spark plugs and wires replaced with no improvement (all needed to be done anyway). Ran a bottle of Techron thru with no improvement. Last year I cleaned-out the idle air control valve after a dying at idle problem, so that should not be it. Could it be an ignition coil? There are 3, so each must control 2 cylinders - is there one that controls cylinders 2 and 4? Thinking about moving them around to see if the error code moves to different cylinders. I am overdue for a timing belt change - could that be it?

Searched thru a number of other posts, but have not been able to find a good match. Any help would be appreciated!!

[chronoti]

P0300 Random/Multiple Cylinder Misfire Detected
P0302 Cylinder 2 Misfire Detected
P0304 Cylinder 4 Misfire Detected

middle coil pack? switch it and see if the code moves

[RKE4]

Last night I switched the middle coil pack w/ the one on the right. Left the wire to the negative terminal on the battery off for a while to clear the existing error codes. Actually running better, but still not right. No CEL yet, so as soon as a code pops I'll check it and see if the problem has moved to other cylinders. We'll see if this does the trick - thanks!

[RKE4]

After switching two of the coils last night, now pulling error codes P0300, P0302, and P0306. Given that cylinder 2 is still misfiring, and now have 6 missing, unless I have multiple bad coils, I'm thinking it must be something else. Was really hoping that it would be one of the coils - that would be a simple fix. Local parts shop thought that maybe original problem was the plugs, but maybe when the garage put in new plugs, they didn't put in double platinum as spec'd by Toyota - so new plugs may not be firing hot enough and thus still causing the problem. Will pull a plug to see what they put in.

Any other ideas?

[zppeacock]

try putting the coil thats on cyl 3 on cyl 2. you have 1 coil per cyl correct?

[RKE4]

No, I only have 3 coils - each controls 2 cylinders.

[RKE4]

So I've been thinking - the only cylinder-specific misfire codes I have had have been on 2, 4, and 6. I don't have a map of the cylinders, but believe those may all be on the same side. Anyone know? If so, what could it be that would be causing problems on one entire side? Wires? I noticed the new spark plug wires that were installed were to one side of the engine - the other side seems to be direct wired from the ignition coils. Is it possible that wiring is bad somewhere? Anyone seen this before?

Any help would be MOST appreciated!!!

[BMR]

Originally Posted by RKE4

So I've been thinking - the only cylinder-specific misfire codes I have had have been on 2, 4, and 6. I don't have a map of the cylinders, but believe those may all be on the same side. Anyone know?

Yes, those are all in the front bank, nearest the radiator.

[RKE4]

Thanks! The plug wires that were replaced were the ones that go to the cylinders nearest the cabin. The ones across the front that you reference, I have heard those are "direct fire". Not sure what that means, but the wires seem to be all bundled/taped together as they head from the coil to the plug. Not sure if they are normally replaced. Is it possible there's a problem w/ one of them, or is there something else I should check?

[RKE4]

Turns-out that it was the ignition coils. Believe the coil on cylinders 3/4 was bad, and may have then in turn put extra stress on the other two. Given the age and miles, decided best just to replace all w/ Toyota OEM replacements. Funny that they all tested within spec, but were not working.