Idle surge, engine power loss brake tapping feeling
07-02-2012, 07:03 PM
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Idle surge, engine power loss brake tapping feeling
2000 F150 ext cab 4x4 XLT
Cold engine starts and runs great
Truck runs fine in cool outside temperatures
Hottest time of day after 20-40 min of driving truck starts giving me this tug feeling/stall/hesitation while driving. Seriously feels like someone taps the breaks then goes away and comes back. When stopped idle will drop from roughly 700 to 200 near stall then surge to 1000rpm and back to normal idle. When this happens accelerating at speed or from stop it hesitates as if truck isn't even running for about 10-15 seconds. When it catches up it returns to reg drivability and problem goes off and on until truck sits for an hour or two or outside temp drops around 84 or less. Fuel filter replaced, no miss fires, no codes ran full diag on computer, replaced throttle position sensor, air filter clean, fuel pressure check and at spec at least not during episodes. Trying to avoid paying a large amount just to get told what the issue is or might be.
Cold engine starts and runs great
Truck runs fine in cool outside temperatures
Hottest time of day after 20-40 min of driving truck starts giving me this tug feeling/stall/hesitation while driving. Seriously feels like someone taps the breaks then goes away and comes back. When stopped idle will drop from roughly 700 to 200 near stall then surge to 1000rpm and back to normal idle. When this happens accelerating at speed or from stop it hesitates as if truck isn't even running for about 10-15 seconds. When it catches up it returns to reg drivability and problem goes off and on until truck sits for an hour or two or outside temp drops around 84 or less. Fuel filter replaced, no miss fires, no codes ran full diag on computer, replaced throttle position sensor, air filter clean, fuel pressure check and at spec at least not during episodes. Trying to avoid paying a large amount just to get told what the issue is or might be.
07-03-2012, 02:56 PM
#2
I have the same issue with my '01 supercrew 4.6... The only time my truck does it is when I'm at a stop light with the A/C on, it drives fine, no CEL's or anything. With the A/C off the idle does not drop at the light or surge. Only A/C on. Weird issue, haven't found it yet... So far I've cleaned the MAF, and replaced the idle-air motor, cleaned the TB, and replaced the fuel pump and fuel filter at the end of November last year. Still surges....
07-03-2012, 03:11 PM
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My 03 just started the same. Rough idle whether A/C is on or off, hot or cold, almost stalls then surges, rough idle till quits. Have new plugs, wires, injectors, coils one year ago. I do have a bad gas cap. Could that cause a problem with fuel pressure? Smells like its flooding. No codes. No Cats!
07-03-2012, 03:43 PM
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Thought about the cats but doesnt do it all the time, only when hot. Thought about crank sensor but i can put it in nutrual at a stop light and still get an an rpm drop then surge. I have been told that majority of the time if there is a driveability issue and no codes its a fuel supply. Most the time sensors should throw a code too so im not sure where to go next. Your o2 sensors never threw a code after dropping the cats???
07-03-2012, 03:51 PM
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Bad gass cap could throw a check engine too. You looked into the coolant temp sensor? When the engine is warm or cold it sends signals to computer and the computer will controll the amount of fuel whether rich or lean pending engine temp. If it malfunctions the truck could continue to run rich even when engine is warm and cause bad gas milliage burning fuel and flooding. Ive heard vacuum leaks could cause simular symptoms.
07-03-2012, 10:05 PM
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Ok update, so i talked to some 16 year experienced tech and a few others from experience with some of the current symptoms and they claim that its the fuel pump going bad. I ran a pressure test off the fuel rail near injectors and was within the 28-40psi idle spec for the 5.4l but the truck had been sitting for a few hours and the issues in question were not occurring. I went and purchased a pressure tester with the ford adaptor for $45 and connected it. Run it up under hood to windshield so can be seen from divers seat. Next time its nice and hot out and the issues come back ill be able to narrow down at least whether or not its a fuel issue. Fuel filter already replaced so this will tell us it the pump is going bad and malfunctioning when its hot out. Will post results.
07-05-2012, 11:18 PM
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Originally Posted by scott516
My 03 just started the same. Rough idle whether A/C is on or off, hot or cold, almost stalls then surges, rough idle till quits. Have new plugs, wires, injectors, coils one year ago. I do have a bad gas cap. Could that cause a problem with fuel pressure? Smells like its flooding. No codes. No Cats!
HELP!
