2000 LR Disco II with Secondary Air - 106,300 miles

Truck will idle fine. While parked... if I rev the engine via the throttle... let off for a second while it's slowing down... then throttle up again quickly I'll get the backfire in the intake. When on the road... if I let the truck run own it's own in drive or only slightly apply gas seems to be ok. When I press the gas like I normally would... intake is loud and when I apply more gas I get the backfire. I'm not sure if I'm describing this right but it seems like the gas to air ratio is not right.

• Replaced MAF Sensor (this week)
• Replaced plugs (Champion this week)
• Wires replaced (6 months ago - from Advance Auto - not Magnecor)
• Composite Head Gaskets (6 months ago)
• Rest of the gaskets from Atlantic British Kit (6 months ago)
• Head & Valve Job done (6 months ago)

After having Advance Auto clear the codes again... took it back yesterday and got the following:

• P1300
• P0305 (twice)
• P0306
• P1590 (twice)

Where do I go from here?

 

First how were the valves adjusted??
Is it possible that the valves may not be seating due to tight clearances?? A compression test will confirm this do it when the engine it hot.

You may have a sticking valve try adding some marvel mystery oil to the oil about 1 qt should do then drive the truck
Also consider add some techron to the fuel

 

Head Shop in Atlanta did them

 

So you have a misfire on 5 and 6. I would try some new quality wires (kingsborne if on a budget) and make sure 5 and 6 wires are on the correct coil though I doubt they mess with the wires when they did your plugs.

1590 is a code for your 3 amigos.