1997 Ford F-150 97 F-150 Idles Rough / Misses, Sometimes Star

JEFFCEO

MEMBER
1997 FORD F-150
6 CYL
4WD
AUTOMATIC
90,200 MILES

Hello,

Everyone has been stumped with this problem, I hope you can help. This is the 4.2L V6. Lower and upper intake gaskets have been replaced.

The truck idles rough or possibly misses at idle. Enough to feel the seemingly random miss in the steering wheel and seat. The engine also jerks due to the issue. No check engine light. Sometimes when started truck will shake and stall but restart fine.

I have done plugs (champion) and wires, idle air control valve, cleaned the egr ports and checked fuel injectors, replaced driver side upstream O2 and swapped in a new passenger side O2, swapped in a new coil pack, fuel filter, checked all vacuum lines and PCV, cleaned MAF and tried a brand new one, vacuum at manifold 18.5-19.5 in., fuel pressure good, seems to be getting poor gas mileage.

Spark plugs seemed dirty to me, here is a picture: http://picasaweb.google.com/jeffceo24/Truck/photo#5116765817055358610

Please help, I am making a donation!

Thank You

1 Reply

MERLIN2021

MECHANIC
17,250 POSTS

Get a can of spray gumout, start the car and spray around, pay attention to vacuum lines and manifold, if the idle changes, you found a leak. You want the engine running and spray on the outside but do direct the stream onto the hoses, if it is a vacuum leak, the engine idle will change speed, then you have detected a leak, repair the vacuum leak and see how it runs!

Poor mileage and these symtoms, I suspect a vacuum leak and or the need for a tune up!
Pay particular attention to the new intake!
Have you checked the fuel pressure yet? These plugs tell a tale of a rich running motor. Have a look at the fuel pressure regulator, unplug the vacuum line see if there is any gas in the vacuum hose, if there is, replace it.