I bought the suburban, it's a 99, 275,000 miles
It runs great when it's cold, fires right up no smoke soundsvery crisp, after it warms up to 160 deg or so, it will barely idle with clouds of blue smoke and lopes like an old alcohol digger. It will roll down the highway on cruise just perfectly. First thing i did was plug in a good fsd on a cooler, from my pkup so i knew that was good.
To drive it you have to give it a foot full, it chugs bad and clouds of smelly unburnt fuel smoke until it gets over 1500,. Then clears itself, and runs really nice. Power is good, motor is smooth, If i two foot it i can keep it firing on all 8 with no smoke, but thats pretty hard on the brakes.
I can bring the rpm up under no load and it cleans up a runs great at 2000
The codes its giving are

PO 1214
P 236
PO 1214pd (?)

So it seems like its going waay retarded, at anything less than 1500?
Some things i read point towards a stepper valve?

Any input would be greatly appreciated,.

Thankyou
Nick