Hey guys, Ive got a real stumper of a problem that I need some help with. First off I'll start with saying that I'm not new to the automotive world, Ive sold parts for quite a few years and am now an auto teacher. However this misfire has got me stumped on where to go next. The vehicle is a 1992 Chevrolet K1500 with a 350 cid. The truck has 247k miles but the engine only has 110k.. The plugs and wires are new (2 sets actually, thought that was the cause), new TBI base gaskets, New cap and rotor, compression test good.. newer fuel filter.. Fuel pump and ignition module are less than a year old.. Okay so the issue arises when coming to a stop at a light when the vehicle sits for a few seconds and the rpms drop to the in-gear idle speed.. It is not consistent, just kind of a random "bump" but a definite miss.. No miss under load (accelerating) which is common for wires.. I was thinking maybe injector, pressure regulator, intake manifold gasket or distributor but I dont want to start replacing parts just because.

Also I noticed when towing my camper it will chug/jerk at around 40-45 mph (fairly low rpms), but go away when over or under that speed.. I was thinking maybe torque converter but once again, I dont want to just replace it because it might be bad..

If anyone can help it will be greatly appreciated! Like I said, I know my way around a car but this is just weird! Maybe someone has seen this before.. Thanks!

Intake gasket/air leak.

Have you checked the injectors ? You might try a can of seafoam through 3-4 tanks of gas .

But first pull the air cleaner and make sure your getting a good even pattern out of your throttle body injector . If they are carboned up , gas can build up and at higher idle vacuum a drop or two of gas will drip off , causing your problem .

How do the plugs look ? Plugs can tell you a lot about whats going on inside .

Are they black and sooty ? That would indicate a possible fuel problem .

If they are white , you may have a vacuum leak . If one plug looks different than the rest , start your search with everything associated with that cylinder .

If one is really clean , look for a antifreeze leak , probably your intake gasket .

I had a 95 chevy blazer with a 4.3 that had similar random misfires but would run fine most of the time. Every once in awhile I would smell gas but could never locate a leak...

It ended up being a plastic gas line leading to the injectors inside the intake that had cracked. It was dumping gas into the intake. It was very obvious what was wrong once we took the intake off

Sparkplugs tell a lot, as you already know. I'd want to see the plugs, but if all else is ok with the ign system & engine mechanical, I'd have to say air/fuel ratio for some reason. I also am leaning to an internal vac leak. (20 yrs GM experience)

And the winner is........ Intake!!! Grabbed a can of brake clean and sprayed around the edges. Apparently its worse than I thought as there is about 3 different ports that are sucking air... When I changed the plugs a few weeks ago they looked pretty good but a little on the whitish side, proving the lean burn theory.. Thanks for all your input guys!