Q: Rough Idle After Engine has Heated up.

asked by on December 27, 2016

Been having this issue with a 2007 F-150 (5.4L 3v) I bought back in July of 2016. When I start the truck cold, it will idle fine, can drive it, start, stop, and it will operate smoothly. Once it warms up though (after maybe 10 minutes of driving (and the temperature gauge is at the middle point), when slowing down or at a stop, the engine will idle down and shake the whole truck, and an audible knocking can be heard (until RPM > 1500) (at this point the timing is jumping all over the place, though is generally far too advanced for the rpm). At this point, if you turn the truck off and back on again, it will idle fine UNTIL you rev the engine at all, at which point the truck will start shaking again, and idling really rough.

I noticed that when I unplug the pigtail connector from the VCT Solenoid in the valve cover (as it's rough idling), the engine starts running fine after a restart (this is because the PCM detects a fault, and puts the timing in a default position I think).

My car has 128000 miles.
My car has an automatic transmission.

Hi there. Check the engine oil pressure. When the oil is cold, it is thick and when its warm its thinned out. If the oil pressure drops lower than 25 psi, then the variable valve timing solenoids will not work. If the oil pressure is low, then change out the engine oil and add a thicker engine oil and new filter. If the problem still continues, then check the engine oil when the engine is first started and then check it again as the engine is running rough. If the oil pressure is low and then increases as the throttle is pushed down, then the bearings on the crankshaft are worn out and need replaced. If the oil pressure is low all the time, then either the oil pump is failing or there is a blockage in the engine. I recommend replacing the variable valve timing solenoids if they are still not working. If you need further assistance with your engine running rough after 10 minutes of driving, then seek out a professional, such as one from Your Mechanic, to help you.

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