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Ron, ASE Certified Technician
Category: Ford
Satisfied Customers: 23001
Experience:  23 years with Ford specializing in drivability and electrical and AC. Ford certs and ASE Certs
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My 97 f150 all of a sudden started idling rough when I

Customer Question

my 97 f150 all of a sudden started idling rough when I started it today. It is doing a continuous rev up and down while it is idling. Also noticed the smell of gasoline after running the engine for a little bit
JA: Is the rough idle intermittent or consistent?
Customer: its consistant rough idle. Like it is trying to stay at correct RPMs but not able to hold correct idle speeds
JA: What is the model of your '97 Ford?
Customer: 5.4 litre v8 ford F-150
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: yes I plan to. I checked fuses and searched for vacuum leaks and thinking of possible IAC or TPS sensor fail
JA: Anything else you think the mechanic should know?
Customer: when I give it gas, it will rev up and run okay but I do get the smell of gasoline while it is idling rough so I am also thinking it may be something to do with spark plug failure causing misfires or possibly a fuel filter or fuel pump going out?
Submitted: 2 months ago.
Category: Ford
Expert:  EricFromCT replied 2 months ago.

Hi. The two common causes are the IAC valve and a vacuum leak. Commonly the pcv hose on the passenger side valve cover gets a sucked in elbow connector on the back of the engine. But if you have checked for vacuum leaks the IAC would need to be replaced next.

Customer: replied 2 months ago.
but would IAC cause the smell of gasoline to happen when it is idling rough?
Expert:  EricFromCT replied 2 months ago.

if the idle is going real low its possible the fuel is not being burned correctly.

Expert:  EricFromCT replied 2 months ago.

if you have a fuel pressure gage you can check that

Customer: replied 2 months ago.
yeah I dont have a fuel pressure gage but I was thinking of checking the fuel pressure regulator now and seeing if there is a problem with that. sounds like its not getting a ssteady fuel supply to the engine. one thing i have read on was the fuel regulator diaphram could be bad causing fuel to run up into the vacuum line attached to the regulator and causing the vacuum to be flooded with fuel. let me know If you think that sounds like a legit cause for my symtoms. im going to step outside and look at it
Expert:  EricFromCT replied 2 months ago.

the diaphram can be bad. usually does not cause a fluctuating idle. to check it just remove the vacuum hose and see if it is fuel soaked.

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