Join Date: Nov 2007
Location: Parker Colorado, USA, directly above the center of the earth
How many miles? Have you pulled the plugs and looked at the intake for carbon buildup? That is known to restrict flow and power.
Have you taken a look at the HPFP? They have been known to "fail" and still function. they can leak fuel into the oil or just not put out as much as they are rated for. Reduced fuel delivery will result in the ECM detuning the car. While you are at it, consider putting a gauge on the fuel hose from the tank. Make sure the in tank fuel pump is working to specs.
Have you looked at the throttle body? They can accumulate dirt over time and that can restrict the function.
Have you checked the PCV nipple on the hose to the air filter? Sometimes these break, then leak and affect the tune.
Check the connectors to the intake sensors. Never know.
Cleaned the MAF lately or ever?