Hey guys...even though this is my first post as a new member, I have been reading your threads and posts for several months and using them to diagnose and or repair my baby. THANK YOU FOR ALL YOUR HELP! THIS PLACE IS AWESOME! However, I've taken all suggestions I could find on this problem and now...I have to ask for more help.

About six months ago my truck started to vibrate, in gear, at a stop light. At times, the vibration was so bad that I thought the rear window was going to crack. I searched for fixes and found many threads here to refer to and performed the following 'fixes' with little or no progress.

Over the past several months, I've done the following:

-Replaced the air filter (it was a disaster)
-Used A LOT of injector cleaner
-Replaced the plugs
-Cleaned the Mass Air Flow Sensor
-Cleaned the throttle body
-Replaced the PCV valve
-Tried a new IAC (it wasnt the prob so I returned it)
-Tried a new Throttle Position Sensor (it wasnt the prob so I returned it)

WHAT ELSE CAN BE CAUSING THIS?

I am very mechanically inclined and can perform most repairs on my own, IF, I know what to repair. But as of now, I am at a loss.

Please help.
Thank you!

 

Sounds like you could have a vacuum leak. Check all the hoses and elbows. I had a very similar problem, and it was a tiny rubber elbow. I'll see if I can find the thread/pictures I posted.

 

Check this out... https://www.f150forum.com/f6/97-roug...x2/#post443622

 

Thanks JT...I have read about a vacuum leak being a possibility and I have checked a few elbows, which looked ok, but I don't recall there being an elbow in the same position as indicated in your photos, but I TOTALLY could be wrong. I might have overlooked it. I will check it in the morning. What year is your F150?

In addition to the list of 'fixes' I tried, I thought I'd mention I also had a mechanic friend check to see if there were any manifold/intake leaks. He also scoped it with a camera...said it was dirty, but no leaks.

I'll get back to you on the elbow check.

Thanks man

 

JT,

I have a 4.2L V6 - it's not the same as the pics you showed, but I searched for similar 'elbows' and could not find any except on the PCV valve at the valve cover...which was ok - (I replaced the PCV valve about a month or so ago with no improvement)

I also attached three pics of my engine for you to look at. Please let me know where I should focus my attention, because I am still totally at a loss as to where to go from here.

Thanks man.

 

ok so iv noticed your problem several times before while working on cars ect. how many miles does your truck have i have a 98 f150 4.2 and what iv heard from my instructors is that on these 4.2 when u get up into the high miles is that the ignition coil gets weak. now dont hold me to that this is the first ford i have owened and i work on mostly chevys but it could be worth giving it a shot

 

mine did that when i had a bad/weak coil pack on #3, i would suggest trying the coil, it may be weak/bad
hope this helps

 

If you think it is a coil pack dont go buy one and try it. Instead pull one plug wire and start it if it is worse then you know that one is working. do this to all of them. when you think you have found the bad one that when you pull there is no difference at idle, then pull the spark plug and compare to another one. If there is a difference you found the problem.

 

My truck's Odometer says 72K, but given the rust underneath I suspect the instrument cluster might have been replaced, but that could be my conspiracy theorist side coming through. Other than this idle problem the truck runs nicely! Remember it's ten years old too.

Perskem...I think I'll try that. When pulling the wires...if I pull one and there is no change, then that one wasn't functioning right all along. Therefore I should pull the plug and compare it to a plug from a cylinder which was working correctly? If I ID the bad wire/part of coil by doing this, what would be the purpose of comparing the plugs?

 

that would work, or if you can get your hands on a osiloscope (dont know how to spell it) you could read each cylinder to see if its firing correctly, even if the fire is weaker/stronger than the others.. but i doubt you can get one of those unless you have friends in a high end shop, or you work in one.. thats how i figured out my coil was trashed on my '96. those things are sweet!