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Truck idles rough it gets worse when its rainy and damp

At first I thought it was a vacuum that was causing all of this.I was getting a (small leak) code I replaced the vac tubes and the code still came back.
But that is not the main problem.I had two problems at the same time I just didn’t know it. A vac leak wold not make it run this bad.
I had just recently put in new plugs and found one plug loose. It was easy to take out and didn’t need to be broken free.The plug was fouled out bad (black) the other 4 were good. It must have been the loose plug all a long that was giving me problems. I drove the truck a while before I checked the plugs,I had no clue it was loose.
When the plug job was done,it ran well (because engine was warm) the next day with a cold start it ran bad,real rough. I was thinking that the loose fouled plug caused the coil pack to over load and go bad…Now when the weather is wet it makes it way worse.At least when it is dry I can drive it.
Do you think the coil packs could be the problem creating the missing and rough idle??

There is only 70k on the truck I bought it new in 2002

                                                                                                Thanks in advance for any info  Rick W

Well, the thing about these Freightliners is…
Seriously, what’s the make, model, engine, code(s), and how is the truck used?
What was the manufacturer’s recommended sparkplug change mileage?
Any other symptoms?

The black plug, was it dry or wet?
Did you “chase” the sparkplug threads before putting a new plug in?
Have you changed plugs before?
Did you use a torque wrench?

Post back. I’m not trying to give you a hard time, the answers could help solve the problem.

I’m not even a back yard maniacal man :slight_smile: I just know a tinny little bit about the subject. My Friend is the guy that knows his stuff,but he knows mostly about the (old wagons) not the new computer run ships.

The plug was dry and black
No torque Wrench
and no :Chase" the threads, what ever that means.

Its a Chevy S10 4 cylinder 5 speed 2 wheel drive

and yes I have changed plugs before im 54 years old :wink:

I have run into this problem many times and it’s usually always ignition related. I have one question: When is the last time you put a new set of spark plug wires on your S-10? Spark plug wires have a tendency to “ground out” when conditions are damp or wet as they age. This will cause a very rough idle and the engine will easily stall out if it’s real bad.

This sounds like an ignition (spark) problem to me. It is quite possible the loose plug is related, esp if it wasn’t make a good ground with the engine. Coil damage could result. Have you had the DTC (computer codes read? That’s probably the place to start. If you post them here, folks with more expertise on this kind of problem than I will offer up some guidance I expect.

BTW, a vacuum problem can often result if very poor performance, especially low speed accelerations and idling. Don’t discount that as a cause. Make sure you find and fix whatever was causing it. It might not be a vacuum hose that is leaking, it could be any of the vacuum operated devices that have sprung a leak, like the brake booster diaphram.

I just posted a long reply to your comments and it did not post

Thanks for responding guys.

To the wire question–I did have new wires when I put the plugs in but we started it after all the plugs were in and it sounded good no missing no rough idle.We decided not to put the wires in. I guess we should put them on huh?

The brake Booster diaphram.? is that also called a “grommet” a rubber piece?

There are no codes coming up as of yet. The only code I have seen since all of this started was a P code (small leak) Evap I forget the whole number .I replaced the vac line that was rotted and cracked and the code came back. But a mechanic told me that a vac leak will not make it run bad like that. So it probealy is electric,but what is the culprit?

Are coil packs in a S10 hard to put in? I know its a few bolts to take out.

These links might give you some background info to help solve the evap problem you seem to be having.

Not a grommet. If it is bad the booster gets changed.

Thanks for responding guys

To answer the question about the plug wires. I had the new wires and new plugs ready to put in. The plugs went in first. Then my buddy said lets start it and see how it runs. It ran well,so we did not put the new wires on.It was getting late and it looked like a snake pit getting to the bottom wires. So we didn’t replace them. So I guess I should put them on?

To answer the code question, The only code I got this whole time was a (small leak) a P code I for get the whole number Evap. I took off the neg termnil to reset the computer and no light has come back on.It has been 2 days.
The truck was running fine on the road yesterday, today its rough as hell sounds like crap. I’m afraid to take it on the road today. Like I said the rain makes it worse magnifies it.

The brake booster diaphram ? it that where the vacuum hose from the manifold pushes into? I just used some sea foam and poured into that vacuum hose. is that brake booster piece called a gromit?

some other things I have researched on line that may be possible causes. (or not)
ERG valve stuck
Dirty (back ) of throttle body
o2 censers
coil packs (bad)
EVAP canister purge solenoidal valve stuck or cracked

Like I said,know a little about cars but when it comes to this stuff i’m lost there is to many possibility’s.

Again thanks for the input.fellows I will try a few more things before I take it to a shop.Maybe this place will save me :slight_smile: let me know what ya think Rick

So what you are telling me George is that you think it is still a vac problem? From reading all of the info on the links you sent,there is no way I/we can do all those checks. So it looks like I am going to take it in before I F$#%^k something up and make it worse. Thanks for the INFO guys Rick

I would definitely replace the spark plug wires. Old ones will often work fine when they are warm and dry, but cold and wet and they short out. It’s just not worth discussing much; just do it.

Rick W … these drivablity problems can take some time to solve. They can be solved though, but there are often a dozen or more possible causes that result in the same or similar symptoms. An experienced mechanic can make all the difference in how long it takes to solve b/c they have the correct scan tool and have seen the problem before and so can make an educated guess what to test first. Otherwise it is a hit and miss thing. Start testing one thing at a time. You may get lucky, you may not. But if you go through all the possible causes, it is a mathematical certaintly eventually you will find what is wrong. You may be 85 years old by then, but you’ll find it … lol …

I had a drivablity problem on my Corolla recently, and the folks here on Car Talk forum offered up some good advice which minimized the time I spent. But ultimately I just had to keep on keeping on until I eventually found the problem. You might find my trials and tribulations I went through before finally arriving at the solution humorous and maybe even a little helpful.