My CRD Experienced a slow decline in fuel economy over the past 20k miles. Went from calculating 0 to 1 MPG higher than VIC to calculating 1 to 2 MPG below VIC and reading was 2 MPG lower than before. Transmission has been shifting clunky and slowly getting worse. Other symptom was engine sounded like it was laboring slightly on the interstate and idle was not as smooth. There were no codes thus I was blaming it on fuel quality.
Hooked up ScanGauge about 1k miles ago and saw higher boost on highway than usual by 2 to 3 pounds?? About 700 miles ago MIL came on and I scanned Code P0069. So, I removed and cleaned the MAP sensor and cleared the code. No MIL until about 150 miles ago and noticed that nominal MAP reading at idle was 16.5 to 16.8.
I finally installed a new MAP sensor and nominal MAP reading at idle is now 14.5 to 14.8. Highway boost is back to normal, engine idles very smooth, transmission shifts like new and mileage according to VIC and fuel gauge seems to be back to normal, maybe.
I now think that I should have been watching the nominal MAP reading at idle and replaced the MAP sensor when the reading was around, say, 15.5 rather than waiting for the MIL.
Admittedly I have done a lot of idling and it has been cold here too. But if there is some easy way to test that would be great. How much is the part?