After about 3-4 months of the engine swap 2years ago, there was a telltail miss at idle. Sometimes a black cloud of smoke when flooring the pedal at about 30 mph. Suffered through blackend 02 sensors, check engine lights and smelly exhaust. The intake gasket leaked, it seems the bolt for cylinder #1 had stripped. It did originally torque down. Through some heat cycles the manifold separated a little. Just in the last 5,000 miles the idle became really bad, the spark plugs would get sooty in just 1,000 miles. This engine had about 100 of the bolt holes helicoiled while it was apart, it seems this one bolt was torqued once to often.

Now it idles like a sewing maching, can't even tell it is running. After all of that, it was something so simple. Tried the propane test a number of times over the last several months and never got an inkling of a leak.

Now I'll drop in a new 02 sensor, may need a new cat too, will wait until emissions testing in Jan. to see if the cat will need to be replaced but a sensor for sure.

What a relief, it had become like a hobby, some hours to kill, open the hood and replace this wait a week and repeat the process and try that.

Just need some more tools or another car. Wife wants me to have another car.

Thanks to all for there suggestions.

DanR 94 964 287,000 miles (53,000 on the new engine)