Crappy running engine - What to do next?

[kcackler]

We've got an 86 3/4 ton GMC sierra truck. Since we've hooked up the proper vacuum lines and the choke, the truck is running better, but still not great. We've got a really really rough idle, and that is the main problem.

So, if you had just bought a truck and it was running like crap, what troubleshooting steps would you take, in order? I don't want to go spend money on a tune-up right off the bat if there are other steps that should come first in the troubleshooting process.

Thanks,
Kevin

[chappys4life]

How long has it been sitting? What the motor? Does it have a carb? How many miles? Does it smoke? Is it running like crap at idle then when you hit the gas does smooth out? We need more details.

[kcackler]

Sorry - New to the whole engine scene.

It's been sitting for a year, I'd say. It's got a 350 with a carb, around 150K miles on the truck, and we THINK 150K on the engine too (We think it's the original). No smoke from the engine, but we do have some from the exhaust pipe. I just remembered also that yesterday when we started her to test drive after doing some work, she shot out a nasty mess of old oil all over our driveway from the exhaust pipe. Not sure what that was.

She runs fantastic when we're driving and are using the gas. But as soon as the gas is let go, it gets rough again. Usually the idle isn't bad enough to kill the truck, but a couple of times it has been.

[trenchwarfare]

Swap out all the usuals, you'd be surprised. plugs, wires, oil filter, fuel filter.

[chappys4life]

yeah I would do plugs (bosch), wires, cap/rotor (msd if you can like $30 from napa), do a oil change (rotella is great for testing - walmart), new fuel & air filter. Also put new gas with high octane and a can of sea foam. Also check the timing to.

After that run it and see what happens. Also try going down the street and gunning it. Sea foam is great for cleaning out carbs.

[kcackler]

OK - We'll start working on the general changes today.

Any other advice, please let me know.

What's the best way to check the timing? With a timing light?

[Malo83]

Also check around the base of the Carb for air leaks if it;s a Qjet, also double check the rubber vacuum lines as they get brittle and get breaks in them which will cause leaks

[menace121978]

spray carb cleaner around the base of the carb and vaccum lines and intake. if the idle changes (smooths out) you have a vaccum leak. cheapest easiest way i know of.

[73chevyman]

i do a tune up and make sure the wires are on correctly i had the same problem and i took the aircleaner off and looked at it for 10 mins and figured out what i did i crossed 6 and 8 it was getting dark and i grabbed the wrong one lol just something to think about

[kcackler]

I've got to extend a big huge thanks to all of you guys. We did new plugs and plug wires, new distributor cap and rotor, new belts, new fuel and air filter, and an oil change, and she starts and idles and runs and stops and is all-around performing very well.

She's still got some issues (Electrical, mainly), but I'm VERY happy with how much less than a hundred bucks and a few days of work helped.

Thanks again.

[chappys4life]

glad to hear its running better, those pieces make a huge difference. Sine its been sitting a while I would get the $15 oil change specials from places like advanced and do a few oil changes at like 2,000 miles then get better oil like mobil 1 and run it from then on. Also seafoam is good to help clean out fuel systems. Just one can for a full tank of gas.