HELP! Rough Idle

Ok, so i'm in alberta now with my truck! Just drove across Canada with it. Before I left i Did a tuneup on it, changed plugs, wires, oil, tranny oil, fuel filter, airfilter. She ran great for the whole trip. But now that I'm in calgary she's idleing really rough. I have a bit of an exaust leak, and It really becomes apparent by sound, ... how do i describe this? Every so often it has a "hiccup"? Its hard though, makes the shifter shake, and the whole truck knock a bit... it's rough, but I only feel and hear it happening at idle. If I rev it up a little, it doesn't do it, and at cruising speed it is fine.

Now I have only very basic knowledge of the internal combustion engine, and i'm hopeing someone out there may know whats wrong.

Would the change in altitude make it run differently? (i'm nearly 3000 feet higher above sea level than i was at home). Maybe one of the new parts i put in was bad?... Cause it was running fine before.

any input would help alot! Thanks

carb or fuel injection?

it's a fuel injected 1993

hey iam in alberta too and my truck is fuel injected and sometimes it goes into a rough idle, my truck has been have fuel injection problems for the last while if u figure it out let me know

During tune up did u change o2 sensor?If working properly it should compensate some for difference in O2 at higher altitude.Change rotor button as well?During trip did u shake a wire loose,like a plug wire-recheck those to see if still seated.Sometimes a bad valve will suck in some air and cause a hard miss on idle,especially exhaust valve.bj

Ok, midnightmike suggested checking my plugs, so last night i pulled all my plugs out. On the plug that was in cylander 4, there was like no gap in the plug, it was bent down, and just almost touching the other side. So i grabbed a good ol' flathead and gave it a gap... and now my truck is running like a champ again

h-m-m.If u drove cross country ok with no misses and then truck starts missing and u have a plug with no gap,I think I would try and find out what caused the no gap.Something had to hit that plug pretty hard inside the cylinder to collapse the electrode. BJ

hmm, true, i could have not nocticed it either, because i didn't notice it misfireing as long as i wasn't idleing... and i literally changed the plugs and then jumped on the highway, hotels were off the highway, i never idle'd the whole trip, i wonder if i just didnt notice it...

if not... what could bend the elctrode? ... what do i look for?

or maybe a wire wasn't on tight, and when i pulled all the plugs, i put a wire back on correctly... in any case, it is running good now

U may be right if u were not idling much u would not have noticed a loose wire and if there was a very small gap in the plug it may have been firing enough to get by.