When im sitting at a stop light or stopped for some reason with my truck in drive, it sounds like the truck is idling up and down constantly, but no RPM movement. When sitting in park it does it slightly but not nearly as bad. Not sure if this is anything major, at least hoping not, but if anyone has any input on this situation it would be great to hear about it.

By the way, 03 with 55k on it.

Thanks in advance..

Go to the top right side of the page, there is a search tab, and type in Fuel Pressure Regulator Valve (FPRV) and there will be plenty to read and get you aquainted with the malfunction!

Good luck!

My truck has always done that.

it also happens when you have a lift pump set at more than 12 psi or have a modded cp3 at least in my experiences. does it do it more when cold or hot?

just started about 2 weeks ago when it was fairly hot, i'd say around the 90's, i threw some fuel additive in and hoping that cleans out some possible bad fuel... and i will check on that search from above, thanks guys... anything else anyone thinks of... welcome to hear...