This has happened since I've owned the truck and it has never caused any major issues I'm just curious what is causing it, when I idle it feels like the truck is just kind bouncing and then when I am in drive I let off the brake and it kind of jerks back and forth until I get above 3-5 mph then it goes away, as does the weird idle. Also when I am rolling forward and it is jerking and I shift to neutral the jerking stops but I'm still moving slowly.
Jerking when rolling forward in gear
- Thread starter blackout51
- Start date
RayVoy said:
It's sits pretty steady around 525-550, I'll check with my scan tool next chance i get to know for sure
Seems a bit low for idle speed. I run close to or at 600RPM. Have you cleaned the throttle body lately?? If you are that low and the A/C compressor cycles it will give you a noticable change in rpm and therefor speed.
mrphoenix80 said:
Yeah I cleaned it a couple weeks ago, and it happens when the ac is on or off. As soon as I get above 600 rpm it goes away completely
Removed and cleaned??? If so it may be your throttle body has something wrong with it. However 99.99999% of the time a good cleaning does the trick. The throttle body controls the idle. Your idle seems low to me. The fact the issue goes away over 600 confirms low idle speed.
mrphoenix80 said:
So you think my throttle body may be bad? I always thought it seemed not open when I looked at it running without the intake parts attached. Also I don't know if its related but when I push the gas pedal all the way down it almost feels like the motor is struggling.
Any codes? You may be getting deeper, but hard to tell over the net. If it is struggling, maybe it can't breath? And maybe we are looking at the wrong end of the engine. It gets very hard to tell without data in front of me. I can look to common problems, but when those don't seem to be the issue all I have left is guess work. I hate to guess because if I guess wrong here it costs real $ there. Throwing parts at a problem is not the answer. By the time you replace 1 or2 wrong parts you could pay for hands on diag and have the right answer.
So if your scan tool does data and codes. You could post some of the info from that, and it may point in the right direction.
So if your scan tool does data and codes. You could post some of the info from that, and it may point in the right direction.
mrphoenix80 said:Any codes? You may be getting deeper, but hard to tell over the net. If it is struggling, maybe it can't breath? And maybe we are looking at the wrong end of the engine. It gets very hard to tell without data in front of me. I can look to common problems, but when those don't seem to be the issue all I have left is guess work. I hate to guess because if I guess wrong here it costs real $ there. Throwing parts at a problem is not the answer. By the time you replace 1 or2 wrong parts you could pay for hands on diag and have the right answer.
So if your scan tool does data and codes. You could post some of the info from that, and it may point in the right direction.
Well my fuel gauge sending unit went out so since I'm at 140k I'm getting a whole new ac delco pump installed tomorrow, and just in the last few days my cel came on with a bad cat code which my lower o2 sensor is brand new so I'm thinking the cat went bad.
CaptainXL said:
I'm not entirely sure, it's a red duralast that came in the truck when I bought it, that was going to be the next thing I looked into until the fuel pump and cat became issues.
CaptainXL said:
They both look fine, a little old, but I do know they can go bad inside and show no signs of damage
blackout51 said:
I just reread this from your original post. Are you saying that your moving while the engine is still in neutral? I am wondering if you got sticking shift solenoids. A transmission service might fix this.
The shift in neutral and still moving forward and the shaking stops kinda makes me think motor mounts. Also I wonder if its a misfire. I had the same symptoms as the first post described with out a cel. I swapped a new coil pack in all cylinders with no change then swapped a spark plug in all until I got to five. No visual damage or sings of wear on the plug. Gap was good... But the shaking stopped 
CaptainXL said:
I'll try and put you in the situation I was in, my driveway is a 100ft hill, so I can sit on it and slowly roll forward holding the brake in drive and the car will shake, but when I am rolling and it is shaking I can shift it into neutral and the shaking stops while still rolling at the same speed. And if by transmission service you mean drop the pan and new filter, I had that done back in November I believe, I mean I got a pan with a drain plug so I can drain the pan and add 4-5 new quarts (however many I take out), but I checked the fluid last night and it still looked good, when I changed it, it was really dirty.
dave_stumph said:The shift in neutral and still moving forward and the shaking stops kinda makes me think motor mounts. Also I wonder if its a misfire. I had the same symptoms as the first post described with out a cel. I swapped a new coil pack in all cylinders with no change then swapped a spark plug in all until I got to five. No visual damage or sings of wear on the plug. Gap was good... But the shaking stopped
Well see, I keep reading about if your sitting still with a rough idle and shift to neutral and it goes away then it's the motor mounts and when I am idling in drive and shift into neutral the idle stays the same, it's only when I'm rolling does the shaking/bouncy idle go away. I replaced two of my coils back in October (the two I replaced had a lot of corrosion on them), and that didn't do anything, and I put all new delco plugs in as well, I can go back in and recheck the gap, but I thought I gapped them right when I installed them. As for a misfire I don't think that's it because it really doesn't feel like one, especially since as soon as I touch the gas pedal it completely smoothed out, wouldn't it get worse if it were a misfire and I push the gas?
blackout51 said:
Ok. That makes more sense. Aside from the shaking you might want to bring it in to the dealer to flush it out completely. They use solvents to cleanup sticking solenoids and stuff. You used dexron 6 right?
What happens if you brake torque it?
Mine did the exact same thing as ur describing above.... Also from what I understand your not suppose to re-gap the plugs from new at least I never have?blackout51 said:
dave_stumph said:
Yep. Fine wire plugs like iridium come pregapped from the factory. You just want to check the gap and not try to regap it. They ship with a protective cone around the tip. If the gap is wrong it needs to be returned.
CaptainXL said:
I'll have to look into that, and I believe it has dexron 6 in it, I used valvolines high mileage dexron, by brake torque what do you mean? Hold brake and push gas?
CaptainXL said:
Oh ok I had read about others gapping to a certain size so I regapped the plugs, ill have to check them when I get a chance.
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dave_stumph said:
Ok well hopefully it'll fix it, what gap are yours at now, do you know?
blackout51 said:
If you regapped the plugs they are probably ruined. But check anyway. You might be able to get them back to spec. The iridium patch on both transfer surfaces is very small and very brittle so never touch it. Just hold the feeler qauges next to the gap and see if it looks similar. Dont drag the feeler gauges between the surfaces like old style plugs. As impossible as it seems to do this with any accuracy, that's why they come pregapped from the factory.
blackout51 said:
Factory gapped
. I would buy a new spark and swap it while you check the gaps. Start the truck and if it still shakes, put the new spark in #2 and so on. It will at least eliminate the plugs as the culprit.CaptainXL said:
Well that's not good...I did gap them like old style plugs and could have ruined them by putting to much pressure on them...those are expensive plugs too
blackout51 said:
Its not a big deal unless you wanted the iridium wear characteristics, mainly longer life. Without the iridium tip they will function like any other old style plug. Just replace them again in 30,000 miles. Any damage done to the iridium layer will not affect how the plug works. If your still having problems after installing the plugs don't blame them.
CaptainXL said:
So even with the bigger gap I gave them it will still be ok? Also just as a side note, I got the fuel pump changed today and it made my problems about half as bad as they were before, there still there, but just less noticeable. Also would my plugs have anything to do with my cat going bad?
blackout51 said:
41-103 plugs should be set from the factory at .043. Make sure they are set to that. Larger gaps can damage a coil over time and result in misfires or bad gas mileage. Misfires can damage a cat no doubt.
Are you even sure the plugs were damaged? Got a closeup pic of the end of a couple? You are looking to see if there still is a very small circular patch on the end of the L shaped ground electrode.
CaptainXL said:
Well a while back I did have a pretty bad misfire, that's when I changed to the iridium plugs, ill pull the plugs tomorrow night and take some pictures and measure the gap
dave_stumph said:
We got hit with that big storm yesterday so I didn't get a chance to do anything, hopefully ill get a chance to check things this weekend. On the plus side I am extremely impressed by gm's 4wd, the truck was unbelievable in this snow/sleet/ice
dave_stumph said:
Ok I swapped out the plugs for new ones and it's doing the same exact thing as before, gas mileage got better but idle and shaking are still there
dave_stumph said:
Nope, I rechecked all of my coils and they are working, rechecked all intake manifold bolts, has a new catalytic converter, I just have no idea. I'm about to give up and just go get a dealer look through. The weirdest thing about it is that it is a completely smooth, just bouncy, idle. Also I notice that when I start it up the " bouncy" feeling speeds up and you can feel it in the higher rpms but not when driving.