02TL-S

Original owner 11/19/01
~225,000 miles
Mobil 1 Synthetic since day one

I dealt with random misfire codes for about the last year. At first I replaced all the coil packs and spark plugs and would still get the codes. Then I took it to a shop and he did a fuel injection cleaning. He also showed me the top of the pistons with his fancy Snap-On color camera. You could see where that fuel injector cleaner was hitting the top of the piston and cleaned it off, but I still had carbon around that. He wanted to do it again and run a second cleaning through it, it was $150 so I said no. Time goes by then I took the top cover off the intake and cleaned out all the carbon, that lasted for awhile but eventually got codes again. I then did multiple cans of seafoam through throttle body, gas, and oil. Again that lasted for a while but then it would eventually throw the misfires codes again. You could hear and feel the misfire at idle and when coming to a stop at a stop sign. Since it was time for my timing belt/water pump maintenance I decided to really go at it. I was contemplating taking the heads off so that I could get the carbon build up off the top of the pistons, but I didn't take it that far. Anyway, I took off the entire manifold/throttle body and cleaned it completely. Changed the timing belt, water pump, idlers, tensioner, accessory belts, radiator hoses, and EGR. I also took the valve covers off and adjusted the valves. I replaced everything will all new gaskets, o-rings, and seals. The car runs MUCH better now. It has not thrown a code. The only thing else I can think of is that carbon build up on the top of the pistons. Compression check was within tolerance with all six cylinders.

fsttyms1

My guess is you had a valve too tight causing the misfire code. Carbon buildup on the piston woldnt cause it. (unless it was measurably thick, wich at that point you would have other issues)

02TL-S

What issues do you get when you have a lot of carbon on top of piston. THis would be good to know. There was a thickness of build up. When I had the injector cleaning it made it nice and clean on a certain area of the piston. When I looked at it through the camera it reminded me of taking a water hose and spraying mud off of cement, how it leaves a shelf.......

Maubo

I agree with fsttyms1 that carbon build up is not the cause of misfires. Carbon will cause pinging and maybe some engine de-tuning when the ECM is trying to stop the pinging, but a slightly open valve will cause a misfire at idle. You are lucky to catch it before burning a valve.

TLer trash

That would be my first guess as well.

01tl4tl

any carbon on the pistons after multiple seafoam thru gas tank, and thru MASTER vac port at TB -wont be enought to worry about (you did the oil method too?)
If its actually building layers upon layers of carbon- the compression would rise and the danger of contact with a too tight exhaust valve increases (it opens at the wrong time and farther than spec)

I think it was finally cleaning the egr system thru the manifold did a lot for you
and valve adjust always helps--
yet some people will argue they dont need adjustment at 105!

01tl4tl

seafoam says noobs should repeat in a month/1500-2000 miles to finish off residue
then good for a year/15kmiles

Not surprising your guy wanted to do another cleaning,,we can do same for 10 bucks!

the shine on pistons goes away quickly from combustion byproducts- stuff left behind from additives in gas,,thank E10 for more of that than the old days~
clean intake valve stems and seals are important--see pic on bg44 ad when it pops up-half clean half dirty valve