Engine Troubles, help!

I was out with the truck last week some time and as I am want, I was tearing through some mud and snow and such things. I was attempting to get up a washout when my check engine light decided it could be on w/out asking, and try as I might I couldn't convince it that it was wrong.

The cause: When idling, the engine runs fine. When accelerating, or when the engine is under load (such as driving up a hill), the engine runs fine. Unfortunately when I'm cruising down the street, minding my own business, it does not run fine. In fact it misses quite a bit.

I've recently replaced all the spark plugs, there can't be more than 1,000 miles on this set, and I checked them all to be sure they were okay. With the plugs I replaced the wires, just because I'm that kind of guy. I checked the wires for wear and found nothing. I did not replace the cap and rotor, but an inspection revealed that they are in fact, quite okay. I had the air filter replaced with the oil change I got last week also, so I can't blame that either.

Having eliminated all of the above, I'm left with a complete lack of identifiable cause. Anyone got a direction I can start moving in for a cause to this most heinous abherration?

Thanks,
-Whir

[Gomer]

How about a little more info on the truck?

[Cyclone2]

Yeh, what model, what OS, what processor, how much ram, what kind of mudders? :/

[caddmannq]

One likely source of this problem is an EGR valve hung open by bits of carbon. This really screws up the mixture at mid-throttle (when it should be stone closed.)

However, if this started while you were thrashing over bumps & such, I'd start looking for dislodged vacuum lines, wires, & cracked vacuum/electrical connectors too.

[cracked]

the rotor and distributor might LOOK ok, but it might be wet inside. had the same problem last week and i checked EVERYTHING on the pos, including the distributor, and could not find the problem. then 2 days later, it fires right up no problem. i asked a friend who is a knowledgable mechanic and he said the only thing it could have been was that there was a little water in the distributor and it must have finally evaporated. spray some wd-40 in it if u havent already, see if that helps.

good luck, i know how it is to have a broke truck and not know why.

drew

[Brainchild]

Yeh, what model, what OS, what processor, how much ram, what kind of mudders? :/

LMAO

Check the wire connections on things like the O2 sensor,MAF/MAP sensor,something may have came loose.

Maybe this will help

LMK
Good luck

[bigblue77]

I second what Cadd said. I have seen this a few times in the shop.

Jer

I'm sure the cap and rotor are fine. Took them off and polished them up with emory cloth. Can't be moisture because I had it out today and I didn't drive through any water.

I've also checked all the vacuum lines now, and electrical connections.

I'll check the EGR valve, or at least look at the manual and see what it says about checking it.

Thanks again.

[thekingofpain]

Does it possibly have an oxygen sensor that could go awry?
(Bein in Michigan I doubt it even HAS an oxygen sensor---its a "Calfornia thing")

Yes, it has an oxygen sensor. No, it doesn't work. But it's never worked so I've ruled that out.