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i own a 95 f-150 and it has an intermitten problem with the idle.it will idle high around 1000 to 1200 .i have a standard transmission and i monitor the rpms and my shift pionts with my tach.when it acts up my truck tachs up in every gear faster.at 60 mph in 5 gear i'm doing 3000-3200 rpms.i have replaced the map sensor,throtle air bypass valve,coolant temp sensor,o2 sensor,and the air temp sensor.it seems to be running rich by the residue in the tail pipe.i need some help my milage sucks 10-12 mpg?what is average mpg for a302 with 136000 miles on it?
sounds like a vaccum leak to me, start by checking vaccum lines, if you don't find anything there, it could be a plenum or intake gasket, not knowing what engine, I can't get too specific.
it is a 302 with 5 speed standard tanny. I have spray 3 cans of carb cleaner on and around engine with no idle change?its been in the shop 3 days now and they are stumped.
If you've got black soot in your tailpipe and its really eating gas, have the fuel pressure regulator checked...costs about $20. It that ain't it, maybe the throttle position sensor could cause the idle surging.
It probably is a vacuum problem. When I bought my first truck ('88 F150 std cab long bed with a 351), it idled fine, but I got only about 6 mpg. It was because the map sensor wire had been pulled off the connector, it idle normally after that and the mileage more than tripled.
Blow into the vacuum line from the MAP sensor. If there is any blockage at all it will affect how the MAP sensor reads atmospheric and manifold pressure. Check all the other hoses at the central vacuum T for contamination and ensure they pull vacuum when disconnected. Cheers.
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