Guy's I have a 2004 XJR .When I accelerate hard the car will buck and hesitate like it's not getting gas. It has a p0171 code I have replaced the maf sensor, first with a aftermarket, and the oem. I replaced the o2sensors, fuel filter, both cats and the pcv. I smoked tested the car, and found and fixed some leaks it did get rid of a 0174 code, . My Indy mechanic said it must be the intake manifold gaskets leaking. Could it be anything else? before I start a big job like that I wanted ask the board

 

How many kilometres/miles are on the vehicle?

Is the MIL flashing when the misfire(s) occur?

What is the fuel pressure?

 

Could be various things, such as an air leak or bad coil(s). Keep any coils you change as cheap ones are worse and fail fast.

 

I had codes P0171 and P0174 on my04 XJR with 154k miles. I took a look in the throttle body and it was bad. Black gummy and crusty in there. Removed it cleaned it as well as i could. About 2 cans of TB spray. Reinstalled with a new gasket and all is great now. It was so bad and gunky on the backside and all down the opening under it. The only other things I did before that with no change in code results was cleaned MAF, smoke tested no leaks, and I bought a fuel filter but never installed it.
My car was bucking and kicking at 3000rpm but also displaying restricted performance at the same time. Basically rev limiting.