P0305 Cylinder 5 Misfire goes away after restart

[customcruiser]

2008 LC200 with 282K miles.

I am getting a misfire on #5, replaced plug and coil and have swapped plug and coil from another cylinder hoping misfire would follow but didn't. Compression test was good.

9 times out of 10 when I cold start I have the misfire, I can feel it and shut down. If I don't I get flashing checl engine light.

Once I feel the misfire I shutdown and restart, takes 2-4 restarts and can get it to run without misfire. If engine just ran, restarts run fine with no misfire.

I read possible broken valve spring but my buddy who's owns a shop and is a big toyota guy too thinks it carbon build up not valve spring and says to run Seafoam in tank and do another round in the intake. He did compression test and said all looks good.

It' been 60 days/1,000 miles since he looked at it and it's not getting any better.

Suggestions?? Should I bore scope the cylinder and/or pull valve cover? Or keep using Seafoam?

 

[StephenChelly]

Sorry to say, but these symptoms sound like the headgasket. Specifically the misfire after cold start, as this is when coolant can weep into the cylinder. How many miles on the 08?

 

[customcruiser]

282K. Will check the cylinder with my usb bore scope this week.

I would expect to have coolent in my oil if head gasket but oil was changed after this issue started and it appeared not to be milky

 

[StephenChelly]

282K. Will check the cylinder with my usb bore scope this week.

I would expect to have coolent in my oil if head gasket but oil was changed after this issue started and it appeared not to be milky

The area where most of the failures occur is between the cylinders where there is a coolant flow / water jacket. Hard to say lucky, but I suppose it is, that typically doesn't result in coolant in the oil. Depending on what you see with the boroscope, testing the coolant for combustion gasses, and / or a coolant system pressure check are also possible ways to help narrow it down.

 

[Sandroad]

As an armchair mechanic in this case, I agree with @StephenChelly on the head gasket. Your symptoms are not typical of carbon or spring issues. Let it sit for as long as you can then check with your borescope. You’ll probably find coolant. A small HG leak into a cylinder won’t affect compression much and won’t get into the oil much. I think Blackstone Labs can run coolant tests, but I bet you won’t need to do that with #5 already cold misfiring.