Jerking when under 1000 RPM | Ford Explorer - Ford Ranger Forums - Serious Explorations

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Steven K

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Whenever I slow down and the rpm is under 1000, no pedals being pressed, the RPMs start to go up and down and at sometimes can hit close to 0 and the car feels like its jittering. At higher speed, the RPMs are normal and have no problem driving. I have a 2015 PIU with 120k miles. Do any of these seem to be the culprit? (Spark plugs, throttle body, vacuum leak, PCV valve?). I have a feeling it may be a vacuum leak because there's a weird sound when accelerating like the car is almost gasping for air. Anywhere to check for a leak?

Thanks
 
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KayGee

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If you want to confirm a vacuum leak, you'd want to watch the movement of your ST and LT fuel trims on a scan tool at idle and then while you increase RPMs to 2-3K. Some people also like to use various sprays, just be careful that they aren't harmful to any surfaces they may come into contact with. Some use smoke or propane to find vacuum leaks. YMMV.

Depending on the maintenance history, there are a host of things that should have been done at 100K and are probably due at 120K - spark plugs, coolant, trans fluid, visual check of hoses/wiring, and so on.
 
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Steven K

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Thank you for that information. I already ordered new spark plugs, a PCV valve and new gasket for the intake. On my way home today, the engine completely stopped and went down to zero RPMs. I had to turn the car off and restart it. Does this point to something specifically?
 
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peterk9

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Fuel starvation??
 
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KayGee

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Does this point to something specifically?
It may, but you'd have to troubleshoot further with the vehicle to confirm.

If it doesn't stall in P or N, but does in D when slowing down, it could be trans related - i.e. TC, solenoid, low/dirty fluid.
Could also be air/fuel issue at idle - too much air/too little fuel - vacuum leak/fuel supply - if fuel supply though, one would think it would present at other than idle also, but maybe not.
Could be idle control, air flow, EGR, other bad sensors or wiring - decommissioned police vehicles can be a crapshoot depending on how they were maintained and decommissioned.
 
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