Hi, Looking for a bit of advice.

I changed the engine in my 2005 Animal last year, it was bought with a knackered engine (bottom crank bolt sheared & timing jumped) so I don't know how it was running before this happened. I replaced the 4D56 with a 4D56T (what's the difference?) all ancillaries were swapped over to the replacement engine fuel pump, oil pump, turbo etc etc. Since having it back up and running the cold idle is 1500rpm, after a few miles the revs will drop very very slowly to idle, and it does then always settle to about 850rpm after it has run for 1/2 hour or more. Timing has been checked twice, vacuum lines all checked EGR deleted.

Nothing flashes up on the dash and the truck is quick and responsive no smoke. I'm thinking it must be a sensor but which one and does the fact it's a 4D56T make any difference? Cant see how it could be timing as it does eventually run right.

Another issue which I cant see being related but worth mentioning, now we have the short days, I'm using the lights a lot more and they dim & brighten with revs, new battery fitted a few months ago, so probably just the alternator on it's way out or the belts need tightening a bit. Charges at 14v fine though?

If it's a sensor, you'd probably get the engine management light on - I guess you don't? For a start is the engine management light working? If it is, I'd be suspecting the injector pump is on the way out - do you get black smoke when you floor the throttle? After the idle settles down, when you blip the throttle, does it go straight back to 850rpm, or does it still sit at the 1500rpm mark for a few seconds?

Yes the engine management light is working (comes on with ign) No more black smoke when flooring it than my Mazda B2500 usual older diesel engines give, When I blip the throttle when it has properly warmed up it's fine, (i.e) run for more than about 1/2 hour, anything less it takes a few seconds to settle.