Dont think this is anything serious... My buds chevy does the same thing. Just curious why it is.

I have a 99 5.4 and in drive it idles and runs pretty dang smooth. If I put it in neutral or park while sitting at an idle, the truck kind of stutters and lightly shakes every couple seconds. Nothing like a misfire I dont think, just a quiver. Why would that be?

Has all new plugs, boots/springs, fuel filter.

 

I have it too, I think it's a bad cop.

 

I honestly did not really notice it until I had a COP fail. Massive misfire, then once fixed I am of course super sensitive to any little feel, and thats when I notice it now. Could be another cop maybe... I have no codes and it is fine in drive and all through the entire RPM range. Usually a cop will show bad with a load though.

 

Try this:

Accelerate lightly and get it to go into overdrive and lockup as soon as you can - then accelerate very lightly, not enough to cause a downshift or unlock. If you have any weak cops it will probably stutter.

 

Will do! Can check it in about 30 mins at lunch.

 

Since I did not ever notice it (as far as I know) until I had the COP fail, could that cop be bad out of the box but only slightly bad to cause this idle shudder? Its the easiest one to get to so that is good. Not even sure what brand it is. Its an all grey cop with no markings or any numbers on it, nothing. It was the used car lot I bought it from that replaced it for me under their 30 day warranty.

 

It's possible. However, if you don't get a low grade misfire doing what I suggested, it's probably okay.

 

Mine didn't stutter when I tried it. When I had a bad cop last year the dealer changed it and my plugs. Never noticed it until after that. It started a little while after if I remember correctly. The other 7 are stock 74k on the clock

 

I also just tested it and no studder/shutter/quiver at all through any rpm... Just when sitting idle in neutral or park. And even then it is not that noticeable. Just a slight shake out of the normal rhythm. I'll swing by the auto parts store and see if there is a hidden code, but im thinking its just normal and I am just sensitive since the original COP failure/misfire since I never noticed it until the dealer changed my COP and plug, just like Truckguy did. I have 94k on mine. I did replace the autolite plug that he put in last weekend when I did all new plugs and boots/springs. Did not change anything though. I'll keep an eye on it and see if it gets worse I guess.

 

This has had me stumped for a year! I do not think it is normal though, it never happened before. I'm going to replace all the cops and boots this spring and hopefully it takes care of it.

 

Mine does what Matt's does but way more calmer... rhythmic shake every few seconds at idle. His fix was new cops.

Link

 

Yeah, just every few seconds a little bump you can feel in the seat. Its the same feel as when my COP went completely dead but extremely lighter. When my cop was bad it had no power, could not drive the truck at all, felt like the engine was going to fall out. This is at idle only and not really noticeable in gear, just park/neutral. If it is anything though, it seems like a COP could be the most likely culprit. Wish I had a code to know which one to replace though. I dont want to pay for all of them and I not sure I trust the ebay branded ones. I just had them all out this last weekend too... pain in the butt. Just doing 1 though wont be so bad if thats all I have to do.

 

Yup, I plan on doing oem here. Let me know if you get it fixed

 

Alright, swapped out boots and cops and it's still there.