You can get misfire codes from an EGR valve that's stuck open, flowing exhaust gas at idle but plugged ports are only going to cause possible pinging, not misfires.

I would pull the EGR valve off, it's only two bolts and see if the plunger is stuck open a little. Usually if this is the case, you'll not only have misfires but you'll have a really bad idle, even stalling.

If it's a 6mt, have you mis-shifted to the wrong gear before? Have you let anyone else drive the car? There's not much that would cause misfires on all cylinders.

All this requires is a simple compression or leak down test and you will know what's wrong.

If it's compression related, it will have misfires at idle but should run fine once you hit the gas and bring the rpms up as in normal driving.

Bent valves will cause no smoke or other tell tale signs. Usually they don't make any extra noise. The more you drive it, the worse it will get because if the exhaust valves can't fully seat, you will burn them.

 

I will try this tomorrow as I am off work. Any write ups for the cleaning procedure? Don't want to mess anything up.

Car idles fine no bogging or stalling whatsoever

She is a 6mt, no one ever drives her but me. I have never mis shifted at all or anything even close. Car hardly ever sees anything above 3k.

Kinda stuck on these and don't know if i should leave it alone since the cel hasn't came back and it's been about 120miles.

 

If its fine, I wouldn't do a thing. If it throws the codes again, get a compression check.

 

I hate cars has a valid point on the egr valve being stuck open, only issue with the compression check being performed is that I highly doubt all 6 cylinders have harsh leakage if that was case then the engine would run like pure sh*t and would have large power loss. No threads that I know of on cleaning process. It would be hard to mess something up on cleaning the ports. If u have went 120 miles with out re-code then I would write it off as intermittent failure. That's enough mileage to cover multiple drive cycles

 

Thank you guys , let's hope for the best.

 

All cylinders can have a little compression loss and it will still run ok. Low compression shows up more at idle when the throttle is closed and rpms are low. Dynamic compression goes up when the throttle is open and with higher rpms. That's why during a compression test, opening the throttle will show higher compression readings across the board. You can have random misfires at idle due to the lower dynamic compression and as soon as the throttle is opened and/or rpms increase, the engine will run normal.

You're right, if there was an extreme loss even in one cylinder the car would run horrible. A leakdown test would probably be more valuable.

An extreme case, I cracked a piston in my turbo car when I was young. It was in the ring land area and it lost most of it's ring seal. At idle that cylinder was completely dead. There was so much compression loss that even when I first nailed the throttle it was still running on 5 cylinders. But, as the boost gauge climbed past 10psi that last cylinder would gain enough dynamic compression from the turbo artificially feeding it that it would light off again and if there was any power loss it was not noticeable by the butt dyno. It's an extreme case but it's the same principle.

 

Update: My CEL came back on this morning. No MID or messages this time though (strange?). So I went to o'reilly after work to have them pull the codes for me. It is the same codes as before of course. Sometimes it really sucks being right. That means back to the dealer tomorrow for me. This time it threw the codes after about 300-350+/- miles.

Glad to know the dealer and the warranty company work soo well together

 

Got my car back from the dealer this morning. So far so good but won't really know til after driving it for a while of course. But at the moment no CEL no MID no issues.

He is what the dealer said and listed on the service report:

"Customer states idle rough when cold and check engine comes on.
Possible carbon build up. DTC P0301...P0306, Misfired all cylinders when cold. Crank pattern was not completed. Reset PCM. Cleared and learned crank pattern. Map sensor .76V when engine fully warmed up indicated vavle clearance is within spec's. Performed de-carbon 2 times. Road test 10 miles. Rechecked in the morning engine data list indicated there is no misfire in any cylinder on cold start. Called tech to seek further information on diagnosing the problem. They advised customer continue fuel treatment a few more times and monitor for any misfires condition on start."


The above service was free this time at least since I was there just a couple weeks ago for this issue. So for now I'm just waiting to see if it comes back or not.

 

This is why I hate the dealer. Your codes will come back, trust me. I don't know how they get away with this shit.