I think this is fairly common.... mine does it. You should be safe as long as it stays above 1.5 at idle and goes all the way up when you step on the accelerator pedal.

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1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k