i have a 92 s-10 blazer 4wd vin w. i start it up one day after work and it is shaking pretty badly. once it gets up to 55 it is not as noticable, but still there. it also sounds like it misses on a cylinder. also another time driving it a loud clanking noise is heard several times around the driver front tire. shortly after this it throws a code, turns out to be est(timing) code. this has been clear since thenext time i started it. i have spark everywhere, fuel pressure is great, timing is perfect. i replaced spark plugs and it seemed better for a trip. next time it started same problem. i does not seem to accelerate as quickly, either. i do have an exhaust leak where the catalytic converter would be clamped to the exhaust, before the cat. it has gotten much louder now that this vibration has started. exhaust comes out of the muffler, but intermittently in time with the vibration it seems. it always does this in park, neutral, reverse,drive, all gears. i'm certain it is not front end related, as i have had balljoints, tie rods, and alignment done to both sides. the shop would've noticed something. funny thing is sometimes it is way worse and sometimes just barely noticable, with no correlation to temp. if anyone has any ideas about this please share, this is my only vehicle.

 

I would start by spraying the wires down with a mist of water from a spray bottle when its dark outside. If you see any sparks, replace the wires. I would guess that this is a misfire generated vibration.

You should fix the exhaust leaks, but so long as there aren't any leaks between the engine and the O2 sensor, you shouldn't have any engine problems from the leaks.