Idle problem, dips when coming to stop
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Idle problem, dips when coming to stop
Idle problem, dips when coming to stop
2000 F-150, 4.6 V-8, MT, 81K miles.
When coming to a stop my truck drops from high idle to 700rpm then it will suddenly dip down to 400rpm then come back to 700 and usually stay there. Sometimes it will dip twice but usually it dips just once, and it almost never dips so bad that it stalls. Once it settles at idle it's pretty smooth but there is a slight vibration that seems to indicate something is not quite right. I'm not having any surging problems after I get going.
When driving down the road – any speed above 10mph -- I can put in the clutch and the engine never falls below about 900-950. It is only when the speed drops below 10mph that the idle drops to 700 then does the dip to 400.
This has been a problem that started around the 40K miles mark. I replaced the spark plugs around 45K and that seemed to fix the problem for about 2-3 weeks. I replaced the plugs again around 60K and the fix only seemed to last a couple days. Around 75K I replaced the plugs and the COPs – still hasn't fixed the problem.
The truck is averaging 14mpg overall. When I do a road trip I can get close to 17mpg. When I take off from a stop the truck seems to be lacking in power (I really have to ride the clutch), which would indicate the computer might be making a mixture compensation at idle to prevent the engine from stalling. This problem first seemed to surface right after I did the ill-advised pressure wash. Clearly I good some water down in one of the spark plug wells because it was missing bad when I started it, but after a couple minutes seemed to clear up. Later I read that I may have damaged one of the COPs when the water was down in the well. I did get a rich on one bank OBD code after the pressure washing incident but that code cleared and has not come back again.
Is it my IAC, vacuum leak, something else? I'd like to keep this truck because it is pretty reliable other than this one issue but it's really starting to drive me crazy.
Thanks for taking the time to read all that!
2000 F-150, 4.6 V-8, MT, 81K miles.
When coming to a stop my truck drops from high idle to 700rpm then it will suddenly dip down to 400rpm then come back to 700 and usually stay there. Sometimes it will dip twice but usually it dips just once, and it almost never dips so bad that it stalls. Once it settles at idle it's pretty smooth but there is a slight vibration that seems to indicate something is not quite right. I'm not having any surging problems after I get going.
When driving down the road – any speed above 10mph -- I can put in the clutch and the engine never falls below about 900-950. It is only when the speed drops below 10mph that the idle drops to 700 then does the dip to 400.
This has been a problem that started around the 40K miles mark. I replaced the spark plugs around 45K and that seemed to fix the problem for about 2-3 weeks. I replaced the plugs again around 60K and the fix only seemed to last a couple days. Around 75K I replaced the plugs and the COPs – still hasn't fixed the problem.
The truck is averaging 14mpg overall. When I do a road trip I can get close to 17mpg. When I take off from a stop the truck seems to be lacking in power (I really have to ride the clutch), which would indicate the computer might be making a mixture compensation at idle to prevent the engine from stalling. This problem first seemed to surface right after I did the ill-advised pressure wash. Clearly I good some water down in one of the spark plug wells because it was missing bad when I started it, but after a couple minutes seemed to clear up. Later I read that I may have damaged one of the COPs when the water was down in the well. I did get a rich on one bank OBD code after the pressure washing incident but that code cleared and has not come back again.
Is it my IAC, vacuum leak, something else? I'd like to keep this truck because it is pretty reliable other than this one issue but it's really starting to drive me crazy.
Thanks for taking the time to read all that!
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