Just recently when we start up the diesel it high idles anywhere between 1200~1400 rpm. The temperature gauge stopped working as well.
Any ideas on where to start looking for the problem ????????
Also, this is a stock cummins

Also just noticed the low fuel indicator light isn't working as well.
Interesting that the check engine light hasn't come on yet...........

it won't..... we called that "1/8th tank syndrome". They used to love to fail and hang at about 1/8 tank.... when it was actually empty. Saw lots of tow ins over the years for that one. Reason I always set my trip odometer when I fill. No long term trust in that gauge.

This gets more and more interesting. The "wait to start" light hasn't worked since all of this started also..............

Sounds like a ECM issue, Check for error code P0606. It will effect the WTS light and other gauge stuff too.

Thanks for the reply, The coolant temp. sensor is on the list.

UPDATE
Replaced the coolant temp. sensor, no change.

The temp. gauge does move from dead cold position up to 140 Degrees, but never any higher. Pretty sure it was doing that anyway prior to changing the temp. sensor....
Also at the same time replaced both batteries for different reason.
What's even more interesting is that even with new batteries and after driving around for a couple of days there's still a second or two delay from crank to firing up.
When the truck was bought months ago none of these problems existed.
Still hoping to find out what causing the high idle.

also the wait to start light decided to start working again.........

Since the temp. sending unit has been replaced, as well as both both batteries, the normal start and idle occurs after the truck has been sitting for hours, overnite etc. every time after that, once it's warmed up the idle goes back to 1200~1400. go fiqure......

You need to have it scanned at the dealer with a DRBIII. The generic ones aren't as reliable and don't provide as much information as you can get off the DRB. Off hand I would be looking at the throttle position sensor and all temp sensors for any abnormal readings. Might not be the sensors themselves but the wiring. The low voltage signals can be easily manipulated by adjacent wiring.