Running lean on both banks AND now running hot

[JD]

I have a '99 X EB (4.0 L SOHC) that ran rough when starting on cold mornings for a couple of months. Finally the check engine light tripped with the codes P0171 and P0174 (lean on both sides). There seems to be a lot of discussion on this board about those symtpoms, but it's also running hot as of this weekend. I haven't seen that in reference to anyone else's problem. The temp moves up to max pretty quick if I'm on a hill or doing over 60mph. It cools to almost normal while coasting down hills. I haven't checked the thermostat yet (maybe tonight) or anything else.

Does this sound like a seperate issue? Or could they be related?

 

[TPLYNCH]

Seperate issues. If you haven't already had it done, get the intake manifold o-rings replaced. That's 99.9% the problem with your cold start and lean running conditions. There is an extended warranty program on the parts. Search for 00M12. You may also want to read up on the camshaft tensioners and timing chain cassette problems with the SOHC. One is also covered by 00M12. The other is covered by program 01M01.

Your Temp problems is most likely the thermostat. They seem to last only ~ 60K. I've replaced mine twice in 140K miles.