My 86 Corolla developed an exhaust leak about 3 months ago. Turned out that a couple of bolts at the head were loose. Had to remove the carburetor to get access. Anyway, tightened the bolts according to the service manual and everything was fine until last night. Then I heard that familiar exhaust sound from under the hood. The factory bolts did not have any lock washers. What is the accepted practice when attaching an exhaust manifold to an aluminum head? Should I have used some thread sealant? The head gets very hot. If the bolts still don't hold very long, would using helicoils or keenserts be any better? Which is preferred? Thanks

I am having intermittant hessitation at cruise speed, in my van. When I plug in the diagnostic tool, it shows error code 1345. What can be the cause of this problem within this circuit?