hey there, new to to community hoping to find some help. I have a 93 suburban that recently started running a little rough at idle. did a tune up on it and noticed when i pulled the park plugs, all except number 4 looked good. plug 4 was pretty rusty, and after the new set, about 500 miles in on the new plugs i pulled them and same thing all good except for #4. so i got to thinking head gasket of cracked head. Did a block test (several times) and results were fine. i pulled my valve covers off today to take a look and, rust. the front half looks about normal but the back half have a nice rust layer to them, not terrible but defiantly rusty. im not showing any signs of coolant in my oil, change that religiously at 3000 miles, and like i stated earlier passed the block test. anybody have any ideas?

 

Do a compression check.

 

Ever change the intake manifold gaskets?

 

i plan on doing a compression tomorrow, gotta take the block tester i rented back so i can rent the compression gauge. yes i actually changed the intake about 6 months ago