Let's see here the order of event's. First came of course the obvious possible cures. A new fuel filter and clean the K&N air filter. Too simple, so of course that didn't work. Than took it to a dealer brand new lift pump. Yea you can imagine the cost on that little guy. Still problem continous to get worse. Today I installed a new map sensor and thoght finally it's fixed, and I was wrong. So I need so more suggestions before I half to get a third job to keep paying for all these parts that are not the problem.

 

What is your fuel pressure at start-up, and at idle? Also, what codes is it setting? Without that basic information you will be in a parts tossing contest until you happen upon the problem.

 

I agree with RCW but will give some suggestions. You followed the same paths that I would have. Fuel filter, air filter and MAP. The only other sensors I know of that has an effect on fuel is the Intake air temperature sensor. The Cranksahft position sensor and the Camshaft position sensor should have larger symptoms. I have a 2001 and don't know if the 99's have all of those sensors. I just know that the MAP and the IAT are directly related to fuel economy and performance. The IAT can fail partly but not completely and not set codes. If memory serves me, the IAT is around 40$. The only other suggestions are more pricy and I'd do more homework prior to purchase. The injectors may need cleaning or replacement. What color is your smoke, if any, might indicate a turbo problem. Last but not least, the High pressure pump(injection pump). How hard are your starts and how does she idle. Has your sump temps gone up or are you burning any oil. Does the oil turn balck any quicker now than before. Those questions are driven by loss of compression and blow by. I know that I have went all over the map but hey I am trying and in my experience with this engine, it can be anything. I love mine and hope yours is the simple solution that solves it. Get back to us on what you find.