Diesel Idle Fluctuation When Slowing Down


I just had the injectors and fuel pump housing replaced on my truck. It’s a 2001 GMC 3500 Duramax with 70k miles on it. The dealer did the work for free since GMC has had problems with injectors on these models.

I picked up my truck Friday and it works well, except for one thing: when coming to a stop, foot off the accelerator, no braking, there is a definite fluctuation in the idle (the rpm indicator doesn’t show it, but you can definitely hear it). It did not do this last week before the work was done. I did not notice any loss in power, or anything elso out of the ordinary. It only does it when slowing down and only from 30 to 20 mph. At 20 mph the transmission downshifts and the rpm’s stabilize again. I just took it back and went for a drive with the diesel mechanic who worked on it. He heard it and said it was strange, never ran into something like it. He looked on his computer for an explanation but couldn’t find anything related to it. I ended up leaving it for him to do more diagnostics.

If anyone has any advice for me as to what might be at fault here I would greatly appreciate it.

Thanks again!!