2007 Sport Trac with a rough idle.

[prsoto]

About to go crazy with this truck. 4.6L V-8 runs pretty rough. Then for a few seconds (2-3) it really gets the shakes, and it settles back down for a rough idle (not teeth rattling, but not like it should be). Then for a few seconds it runs smoothly and back to the rough idle. It does these changes at random, not in any particular order, but 90% of the time is idling rough, and the other 10% of the time it gets really shaky or it's silky smooth. ANY IDEAS?

I have replaced fuel filter, all 8 coils and spark plugs, the computer was re-flashed by the local Ford dealer, and the fuel injectors were "professionally" cleaned also by the dealer. Before the computer was re-flashed, it had no codes, and does not show any codes now after the re-flash.

Very slight improvement on the rough idle, but the shakes, smooth, roughness has not gone away.

I'm ready to read your comments and ideas. If i don't get this solved soon, i will be in a straight jacket to lala land. lol

Thanks

 

[BrooklynBay]

Welcome to this forum! I've moved your thread into the 2007+ Sport Trac section. Which brand of plugs & cables did you install?

 

[prsoto]

The spark plugs are AUTOLITE, the coils are brand "X" aftermarket. No spark plug cables required since this engine has coil on top of the spark plugs.

 

[68 GT]

replace the IAC ? (idle air controller)

clean the MAF ? did you put on any aftermarket parts ? cold air intake ???

 

[stylin99]

Does the truck drive ok? What happens when you rev it beyond idle?

Would be curious to see fuel pressure when it's doing that. Bad fuel pump could cause a lack of fuel pressure and causing it to starve itself, but that would cause problems with driveability too.

When it started doing this, was there anything particular that you changed, or might have occured just before it (i.e. cat sleeping in your engine bay, or drove your ST into a lake...)

 

[prsoto]

68 GT: have not tried any of these. i will try and let you know if any luck. All factory stuff in the motor (except the spark plugs and coils).

stylin99: The truck drives OK. When you rev up above idle it runs just fine, and driving around is no problem. It starts with no issues. I bought the truck and it had that problem. i thought it would be something simple (coils or plugs) but it has bitten me in the you know what... When i changed the fuel filter it was pretty clogged. i was surprised with such low mileage (37,000) that it would be that dirty. That makes me suspect a bad (or maybe 2) fuel injector that's possibly not closing/opening when the ECU demands it. but that's just a guess... Any ideas on how to check the injectors without having to replace all of them? Those babies are 70 bucks apiece.