Dirty Intake Manifold

That sort of reminds me of mine. Carbon in the early inch or so of the port, but right beyond where the tip of the fuel injector pokes through, stuff is clean. The detergents in the injected fuel have been doing their job.

Should you worry about that thin carbon coating that's upstream of the injector, where the detergent never hits it?

Well, one of the ways carbon buildup causes a driveability problem is it kind of acts like a sponge for fuel. If it soaks fuel out of the mixture on its way to the cylinder, you can have hesitation and stumbling when cold.

But that's when the carbon is in the path of the fuel mixture. When the carbon is only upstream of where the fuel gets injected, it doesn't concern me much. And that isn't significantly reducing the area of the port or anything.

 

No scrubs nor solvent needed. Long as you wipe towards you, it will be fine. Careful not make any contact with the fuel injectors pointed down from above. It’s the combustion residue, if we had non ethanol fuel everywhere and be able to use it on every fill up, the slimy stuff would be less.

 

I have seen far worse that didn't cause misfires or stumbling. But I would clean given an opportunity.

 

You should be able to see the valves from there without a boroscope. That doesn't look horrible to me at all though. This was mine when I was last in there at around 98k for reference.