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Hey guys, I like many on this part of the forum, own one of these trucks, mine is a 98 with a vortec 350, but I have been curious about a little quirk the truck has. In actuality, it is actually two trucks, my dad also owns one of these trucks, mine has about 186 k on it, his about 190 something, and we have both noticed this quirk. On both trucks, it seems when they are warmed up, especially on a hot day in Utah, at stops, the trucks have a light stumble. The stumble is present in both park and in gear, but is more prevalent in gear, at stops, we can both slide the truck into neutral and the stumble gets a bit better, but not gone. It is enough that it makes a noticeable quiver in something like a beverage in the cup holder, it might even be enough to make jello quiver! I would be surprised if it where a misfire or something like that. I also should note that the engine is dead smooth once you start driving again, and other than the little quiver, the trucks drive completely normal. I just wanted to know if anyone else had this sort of "issue" or if these trucks just do that. Personally I wonder if it has something to do with the slow idle, in gear I think both trucks are running at about 500 - 600 RPM. I have never really noticed the problem when the truck is cold. I hope you guys can give me some good input, thank you and I hope to see some new posts soon!
Stumble like the engine starts running rough? When is the last time the spark plugs, wires, distributor cap and rotor were inspected and/or replaced? It could also be a dirty throttle body or vacuum leak.
If it's more of a vibration, it could be worn out engine mounts. You can pop the hood, give it some throttle and look for noticeable engine movement.
Last edited by Chris94; September 22nd, 2020 at 11:55 AM.
I do not know the last time it had a tune up, like plugs and wires, but what gets me is it only does it when it is warm, and it gets more noticeable the hotter it is outside, on both trucks. I don't think it is a stumble though, the engines don't struggle to run, and it seems to be a fairly rhythmic vibration I guess, I have not checked for things like motor mounts, could they have lost their vibration dampening abilities?
Motor mounts will deteriorate over time, and a lot quicker if covered in oils. They're basically a rubber square with two bars and a tube inside. The transmission mount is also a rubber square with a stud. Replacing the motor mounts is kind of a pain on the V8s.
Edited: It's worth checking out your spark plugs if you're not sure when they were last replaced. They can give you an idea of your engine's health. Check for proper gap, carbon deposits, electrode and ceramic condition, oil residue, etc.
Some components get worse as they heat up because gaps increase, resistance changes, etc and these changes might be out of spec just enough to cause running issues when hot.
Last edited by Chris94; September 22nd, 2020 at 12:48 PM.
I made an edit to my previous post, but probably should have just replied with a new one with my thoughts on why the issue could be worse when the truck is hot. My '98 Tahoe is doing possibly the same thing. If I am in drive and stopped at a long red light, a small vibration will start, and progressively get worse. Enough to vibrate my cracked dash and center console. I haven't looked into the cause as I have been diagnosing other issues with two of my other vehicles. I'm way past due on a lot of maintenance though. (The joy of owning a bunch of old cars)
Thank you, I did not see the edit you made until you just mentioned it. I didn't think much of the plugs, maybe I will take one out since they are easy to get to, and take a picture and post it hear, I am not good at reading plugs. And on your tahoe, that sounds kind of similar to the issue I am having, enough to shake a cracked dash (mine is somehow not cracked), but not super sever.
Here are some pictures. I think this is from cylander #3 i think. Same plug, different angle. .052" gap, I am not sure what it supposed to be. Idle after a few minutes, as you can see this is in park. Looks like 600 -700 RPM. Same story, but now it is in drive. 500 - 600 RPM.
September 21st, 2020, 9:10 PM
Slight stumble
