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So I changed the Spark Plugs on my wife's '03 Rav4 yesterday, and found oil in the spark plug wells.
She was at 140k on the original Denso plugs (I know, I know) so needless to say, it ran a little rough.
I cleaned the MAF with MAF cleaner as well while the intake plenum was off.
Going to start catching up on a lot of maintenance on this thing. I've kept the oil and air filter up to date, and I've flushed the radiator, at least. I'd like to get the TB off to clean it too, but it's a bit more in depth than the time I had allotted right then.

When I pulled the boots on the plugs, there was a lot of old oil in the wells. I stuffed shop rags down with a long screwdriver to sop it all up and then changed the plugs. Plugs were definitely worn, and were pretty white (which I know means it's running lean). New plugs in, buttoned it back up, reattached the battery, and after a few minutes of some pretty rough idling (which I attributed to the ECU relearning) it ran smoother than before.

There was no oil on the firing end of the plugs, just in the wells; all 4 of them. Honestly at least a half inch deep each. While I'm not 'new' to this engine, as we've had it for a few years, I'm not fully versed in the workings of it. (I'm more of a 3.4 V6 4Runner guy.) Oil in all 4 wells seems to me like a head gasket issue. Am I off the mark here? The coolant levels are fine and the temp gauge stays a bit below the middle.
 

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Could be that the valve cover gasket is allowing oil to leak down the spark plug hole. Try replacing the valve cover gasket.
 

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That's definitely easier. Cheaper too.
Any brand to go with? Felpro/OEM, etc?

Sent from my SM-G900V using Tapatalk
I bought the Victor Reinz valve cover gasket and it looks like good quality but never did install it so I sold the part after I traded my 05.
 

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There are round spark plug seals which prevent oil from the valve cover spark plug openings from getting onto the spark plugs - shouldn't be necessary to replace the valve cover gasket, but after doing a bit more research it appears that the gasket and seals are sold as a set: http://www.autozone.com/external-engine/valve-cover-gasket
 

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Oil in all 4 wells seems to me like a head gasket issue. Am I off the mark here?.
The oil is probably just leaking in around the round seals at the top of the spark plug tubes. Without spending a lot of time, I couldn't find a video specifically for your engine, but this video will at least give you an idea of what the problem is.
 

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I found the same problem when I changed my plugs, but it seemed only in #4 . I had a mechanic change the valve cover gasket since it was leaking just a little, but enough that he knocked me back for the registration renewal inspection.
I thought a little oil might have dripped off the valve cover when he removed it and fallen into the tube, but now (about two weeks later) when I changed my plug leads I had a look and there is a little bit in there again, but at least not half an inch – maybe just a couple of drops at the most.
When I did change the plugs I looked carefully at the plug connector and could not see any oil at all on it and I figured that it had not come down from the top. Are there seals at the bottom, where the tube is fitted into the head, or is it a tight press fit during manufacture?
My initial problem – why I changed the plugs and leads – is because when I picked up the car after the valve cover gasket was replaced it had a "machine gun" misfire under load when I moved off in 1st gear (up to about 1500 RPM and after that it was fine, unless I gave it some gas at speed or climbing a hill with extra throttle) and also the occasional hiccup when idling – typical of a bad plug or plug lead. At first, when I was changing the plugs, I thought the oil might have caused the misfire, but as I said, there was no oil at all on the plug connector, and I also hoped that a bad plug was the cause of the misfire. Although it was a very big coincidence indeed that it was running fine until the mechanic removed the valve cover.
So I then suspected a crook lead since #4 plug lead is quite short, and getting the connector out of the tube can strain the lead and tug on the connector at the coil pack end – much better I think to remove the #4 connector from the coil pack if the lead has to come out for a plug change. The other three are not a problem and Toyota could have made #4 lead even just one inch longer! Anyway, I figured that the mechanic had done just that – strained and broken the #4 lead enough to cause the problem. So I changed the leads this afternoon but I didn't try it on the road. It seems to run OK up to neighbor tolerance RPM, but did I detect a very slight rough idle or was it just my imagination? I will know tomorrow when I drive to work and I hope the misfire problem is fixed because other than plugs and leads I can't think what else it could be.
 
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