99 Disco, feels like a misfire when driving, pulled codes PO174B & PO171B (bank 1 & 2 system lean). Anybody ever run into this.

 

You are one code away from needing a new MAF.
How is the truck running, what octane gas are you running, what sort of tune related work has been done on it over the last year or so and how does the transmission shift?
Mike

 

The truck shakes alot during acceleration but at idleit is still noticeable. Just recently had new plugs and wires. 93 octane is used regularly and the tranny shifts fine.

 

what is a normal MAF value

 

I don't have that information.
My old rull of thumb has always been when you get a 174 and a 171 lean code along with a 3rd. or 4th. gear shifting code the MAF is gone.
What is the mileage on the 99 D2, have you changed out your O2's yet?
What plugs and gap did you use when you tuned the engine, have you checked for major vaccum leaks like on the PCV and hoses, have you tried to de-carbon the engine?
Mike

 

I cleared the 171 and 174 codes the day I noticed the misfire, and have driven it several times and the misfire is still present but the codes have yat to return. It had Bosch Platinum +4 in it and I took those out and put in some NGKs BPR5ES plugs gapped at .035. No vacuum leaks that I can tell, and I haven't messed with the o2s ( how could I check those).. and how do you decarbon the engine.

 

It is not the Bosch plugs. When you pulled them out, did you check each one for color or fouling? Don't throw out the plugs, they do have a full refund warranty.
Send me your tele number and I'll call you .
Mike
mikeljacobs@comcast.net

 

I borrowed a MAF from a buddies discovery and took it for a long spin and the problem seems to have gone... Thanks so much for all your help..