Engine miss is killing me!

[avguy]

What was the CEL code - random misfire probably? How did the plugs look - did #4 look much different from the others? Did they have the characteristics of an engine in good condition? Just a couple of things you didn't mention, that I'll ask about (which you've probably already eliminated). The rest of the mouse family living in the air filter/box? And since these critters are good enough to occupy the valve cover, maybe they're even broken through the plastic in the air filter and are moving into the TB. Speaking of which, has that been cleaned of carbon deposits recently? And there's always the TPS as a possibility. Probably none of those things though. If you're still stuck with nowhere else to go how about a vacume test, block test for combustion gas, and a leak-down test? Good luck with it!

[Steverino]

It did have a random misfire code. The plugs looked great and #4 looked no different. I did check the air box and it was clean, the hose from it to the TB had tears in it and a friend gave me a good used one from a 2009 Aveo which is just a bit different but works. I cleaned the TB very well when I changed the intake manifold gaskets and did an in the car cleaning about a year ago also. I use an actual TB cleaner spray and an old tooth brush. I looked at the intake valves through the head when the intake manifold was off and they looked very clean. I was going to put the vacuum gauge on it and do a leak-down test. I am not sure what a block test for combustion gas is?