Uneven Engine RPM at Low Speed

[TC]

My 2001 Duramax has just over 34,000 miles and I am making a short list of items for a dealer look before it goes past 36,000 miles.

One thing I noticed that I haven't seen posted here is a slight fluctuation in the engine rpm's at low speed. I first noticed it on the beach when I was cruising along trying to keep it below 15 mph. The engine has a noticable, but slight, change up and down in rpm's. It really isn't enough to see on the tach, but you can certainly hear it. The same thing happens cruising down country roads at less than 25 mph.

Has anyone else experienced this symptom? I had the idle surge software installed a year ago along with the first version of the cruise control fix. Also, I have a very low air flow in the driver side AC vent. Otherwise, I am a very happy camper. I get around 16.5 mpg running a mix of maybe 60% highway and town and 40% low speed around the ranch and on gravel roads.

[mackin]

TC

Since you were on the beach, was it the air conditioner compressor cycling on and off... Maybe? Mine will fluctuate the idle like you describing.......Check the filter on the airflow I'll be doing mine for other reasons........

MAC

[ 07-08-2002: Message edited by: mackin ]</p>

[matt-max]

or it could be like my early '01 and need a new injector pump because the rail pressure control valve has gone wacky.

[TC]

My truck is a very early model, built during the first week of production in October 2000. I do not believe the rpm fluctuation is caused by the AC compressor. In fact when I first noticed it, I was running along the beach with the windows down and AC off. Otherwise, I have had no problems or issues with the engine. Only the idle surge that almost all of the early trucks had and the software upgrade fixed that.

My fuel filter was changed recently as well as the air filter.

[Dave_WB3FYV]

Mine was surging like that before I got the PCM update last month. I don't know if there is a NEW version of the software, but it's worth asking, the repair bill says Updated Calibration J6355 OJ-6C 1.1, whatever that means... Definately fixed the surge, along with the cruise surge, 1-2 downshift, 4-5 hunting in cruise, etc. The technician (notice I didn't call him a 'mechanic') said he uploaded 2 fixes to my truck, but didn't have the number of the other one handy. One can assume that since they developed an early fix for the idle surge that they have continued to refine it and probably have a new version out there now.
For what it's worth. It'll still be a warranty claim.