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i have a 1999 mercury villager w/ 160k and had a rough idle for the last 30k, i’ve replace spark plugs and wires, whole distributor, fuel filter, pcv valve, air filter, intake manifold gaskets, knock sensor and valve cover gaskets. excellerates very good, but misses in final gear around 70mph intermittently. i still get 20 mpg fuel presure is good i’v cleaned throttile body, iac and mass air flow
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p0300 random misfire- have you checked fuel pressure
with a gauge or checked spark with a spark tester?yes to both. this van doesn’t have a fuel pressure port so i used a tee adapter w/ fuel gauge, it runs about 40 psi and the spark has a good spark.
I have had experiences of “new plug wires” that were much better sitting on store shelf then on my vehicle.
If you have no way to scan to see what pcm is doing for you, it gets to be a bunch of parts being changed with no results. I do know a person that I worked with was having similar issues with the rough idle (similar vehicle) in which he was told they were notorius for idle air control ports plugging up. Turned out to be a vac line to back side of motor causing trouble. A scanner plugged in may help to see what fuel trims are doing to see if that may stir you in right direction. High percentage would show you a possible leak.
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