Rough Idle, Erratic Speedometer
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Joined: Oct 2006
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Rough Idle, Erratic Speedometer
Took my 1999 F-150 V6, 5 spd SC to the dealer to check the Service Engine Soon light. They found 170, 174 and 1000 P codes, but could not repeat error condition.
Since then the light is on constantly. Only operating errors I notice are occassional erratic speedometer operation (indicates 100km/hr, drops to 80 then back to 100) or rough idle after a hot restart. Both problems are intermitent, not repeating every instance.
Diagnosis?
Since then the light is on constantly. Only operating errors I notice are occassional erratic speedometer operation (indicates 100km/hr, drops to 80 then back to 100) or rough idle after a hot restart. Both problems are intermitent, not repeating every instance.
Diagnosis?
Hotshot
Joined: Aug 2002
Posts: 12,679
Likes: 15
From: BC, Canada
The P0171 and 174 are probably due to a vacuum leak.
The most common place for a vacuum leak on a 4.2 is the intake manifold upper plenum, where it bolts to the lower manifold. There are O-ring type seals in there and seals on the bolts. Both of them leak.
The most common place for a vacuum leak on a 4.2 is the intake manifold upper plenum, where it bolts to the lower manifold. There are O-ring type seals in there and seals on the bolts. Both of them leak.
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