My truck has started something new. At about 150-170F it idles up and down (rarum-rarum-rarum) about 30 rpm's. You can see it in the tack as well.

Its never done this before.

Is this something I should have looked at by the dealer? Any ideas what it might be?

Mine does this the worst once the cold weather sets in especially in the "mid warm" condition you describe.
I get blue smoke for awhile till fully warm and then most of the lope goes away.
I write it off as a characteristic of my truck and live with it for now.
Blake

Oh I dont think blue smoke is a good thing.

Bad rail pressure sensor.

Yeah I should call it the "Mac Idle" or something but I just can't stand the thought of being away from it while its being serviced.
I always get a small loaner car and I hate little metal.
Blake

I had a fluctuation in my idle at that same temp zone, when I would stop at a light in drive. Never did it when the temp got above 180 ( by the dash gauge). My fluctuation varied and sometimes was so bad I would put it in neutral...anyway the dealership replaced my fuel pressure regulator and the problem has pretty much gone away. It use to do it pratically every time only the amount of fluctation would change. Since the replacement it will still do it once it a great while but never like it use to. If it does it at all its just a slight fluctuation. There is a proceedure in the manual for testing the reg/idle with a tech 2 - you put it in gear, turn on/off the air condition etc. and there is suppose to be X amount of fluctuation......I copied this and took it to the dealer, said they hadn't heard of it before. Whatever, I got my reg replaced and it fixed it.

mighty

I sent you a pm about that procedure.

Man am I glad I dont have an LLY, those boys have a terrible idle problem.

mighty

I sent you a pm about that procedure.

Man am I glad I dont have an LLY, those boys have a terrible idle problem.
My LLY idles just fine, always has :confused:

DmaxTim, just wait......

Pretty much every tsb has come to fruition on my truck.

Ive had 21 problems repaired and I have 3 more that have cropped up.

Anything you see here in your year will eventually pop its ugly head......

JMO

Actually, the "lope" is usually caused by a faulty FRPCV, located on the back of the injection pump.Bad rail pressure sensor.

Info - 6.6L LB7 Duramax Diesel Fuel Pressure Regulator Replacement #03-06-04-010 - (Jan 17, 2003)

6.6L LB7 Duramax™ Diesel Fuel Pressure Regulator Replacement

2001-2003 Chevrolet Silverado 2500/3500 Series Models

2003 Chevrolet Kodiak C4500/C5500 Series Models

2001-2003 GMC Sierra 2500/3500 Series Models

2003 GMC Topkick C4500/C5500 Series Models

with 6.6L Duramax™ Diesel Engine (VIN 1 -- RPO LB7)

The fuel pressure regulator, P/N 97728979, is now serviceable separate from the fuel injection pump.


http://service.gm.com/engif/000/000/952/952814.gif
http://service.gm.com/tif.gif (http://service.gm.com/servlets/RetrieveTif?pic=952814)


If the Service Manual diagnostics lead to the replacement of the fuel pressure regulator, inspect the inner tip of the regulator (see illustration) for corrosion upon its removal. The inner tip of a fuel pressure regulator from an uncontaminated fuel system will be smooth with tan colored fuel deposits, but it will not be blackened with heavy scaling or pitting.

If blackened corrosion and pitting is found on the inner tip of the regulator, the integrity of the fuel injection pump has been compromised and the pump must be replaced. Replace the fuel filter element and clean the fuel system using Service Manual procedures. Injector replacement is not necessary, as the fuel injection pump is the most susceptible component to corrosion damage. After repairs are completed, re-evaluate the vehicle's performance to ensure no additional concerns are present. Some fuel additives emulsify water into the fuel and allow the water to get past the fuel filter/water separator. Fuel additives can be introduced by the customer or by the fuel retailer. Advise the customer of possible fuel source issues and recommend against the use of aftermarket fuel additives.

<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1227270&psdid=297&evc=sm#ss1-1227270">Parts Information

<TABLE width="100%" border=1><TBODY><TR><TH vAlign=bottom align=middle>Part Number

</TH><TH vAlign=bottom align=middle>Description

</TH></TR><TR><TD vAlign=center align=middle>97728979

</TD><TD vAlign=center align=middle>Fuel Pressure Regulator

</TD></TR></TBODY></TABLE>

Parts are currently available from GMSPO.