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oil on spark plug threads related to p0301 and p0353?


New member
2007 avalon LE, 189k miles.

Don't know maintenance history. Has not been to dealer service since 2010.

Got it three months ago (gift from wife's family to her) and it's been fine around town for us. West central florida. It was shipped here from Delaware. That is where it was bought new and her family used it.

I did much routine maintenance on it in those three months. It was making loud clicking noise, which this engine is known for, but once I changed the engine oil and ran it for awhile it quieted down. I think oil was too thick. Both engine and trans-axle oils had been recently changed, but since I did not know what was used, I changed them again. Both were over full when we got the car.

I also fully bleed the brakes. The peddle was very hard and pushed down very slowly while bleeding both rears. After bleeding all, the peddle still feels mushy. Ive literally fully bleed brakes maybe 15 times in my life and Ive never experienced either of those.

Front three spark plugs looked fine, except they were 0.040". I left them there. I didn't check the rear 3.

We set out to go to ohio and after 90 minutes it started to shake intermittently for a few seconds at a time and after a while engine and VSC and stability lights came on. Sometimes the engine light flashed. Decided to turn around and go home. On entire trip home I never felt the shake, but it might have still been doing it just less so.

A few days later went to two different auto parts stores and used their code reader and at 1st store he said "its mis firing on cyl 4....and 6...and 1 and 2....and 5...and #3. It's misfiring on all cyl." I never asked him for the codes. Then I drove directly to other store and he said p0353 and p0300. Then he mentioned the OCV.

A few days later I drove to another auto parts store and they gave me printout: p0301, secondary DTC p0300, p0301, p0302, p0303, p0304, p0305, p0306, p0353, and c1201. printout listed suggested fixes: replace ignition coils, reset ECM (for c1201).

The shake was always very mild and at 1st I thought it was suspension/alignment. We got two new (used tires) installed a few days before the trip. Yes I checked the bolt torque when we got home, then again before we left. Im convinced that it was never misfiring on more then one cyl at a time. It happened at different highway speeds between 60 and 75. That's as slow and as fast as I traveled, so Im not saying it would not happen above or below those speeds.

I removed the WW motor and tray and intake manifold. I planned (and still do) to replace all 3 rear COPs. However, I don't expect to find the problem thru testing in drvway since it was intermittent, but still I wanted to check some other things. COPs for rear cyl 1 and 3 the electrical plug tabs broke off when pressed with my thumb. All three were plugged in tight. # 3 and # 5 cyl rear spark plugs the threads are glossy, like they had oil on them. #1 was wet with oil. See pics attached. Notice for cyl #1 the oil is not on the lower threads and it's stained in the middle. These were also set to 0.040" and I decided that I should gap them all to the proper spec 0.043. I gaped and replaced them. Over night I decided to swap the rear plugs with the front (and gap those too), so if she codes Ill see if it moved to front bank. When removing cyl # 1, I see it's much more wet with oil and the oil goes all the way down to the gasket. How'd it get worse over night? I didnt drive the car. So, maybe the spark plug hole was full of oil. yuck. But the plug ceramic was not oily. hmmm

Since then ive read what looks like toyota docs online saying don't adjust the plugs.

p0301 is cyl #1.

The rear middle plug (p0353) was not torqued, it was just hand tight, but seated. The rear driver side plug (#5) was not even seated. These two plug electrodes look exactly the same as the front plugs that were all tight. The only plug that's electrode looks different is cyl #1, the one with wet threads.

Plugs are ngk Dilfr6d11.

gas cap don't feel very tight, so Im going to get OEM replacement.

It looks like I should remove the valve cover and spark plug tubes and replace the thread sealant. That's a job i don't know if I'm up to.

Several things Ive read say one code might cause many or all of these other codes and that p035x should be fixed first, before looking into p030x codes. But that means putting her all back together to see if she still has this intermittent issue. Then taking her apart again...

I checked voltage between COP wire harness contact # 1 and # 4, between #1 and ground, and ohms between # 4 and gnd. All fine.

I cant find info on what to check on the injector's wire harness contacts without running the engine. I saw wire diagram showing that one of the contacts is common on all 6 plugs, Id like to test that, but dont know which contact it is. Each injector measures 13.2 ohms.

All vacuum hoses look fine.

Saw no physical issues with wire harness. I removed and cleaned the battery to chassis and chassis to engine and chassis to trans grounds.



cyl#1 plug
cyl plugs #3 and #5


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