Hey guys,
I have a 1998 4.6L F150 that recently has developed a rough idle when the truck is in gear. It runs fine when it is in park. I noticed today at a stop light the truck was even shaking a bit from the rough idle and when i went to take off my CEL flashed a few times then went away as I gained speed. I have heard everything such as bad coil packs, bad plugs, bad wires, and now after looking around on the site i am seeing info about a dirty IAC. Does anyone have any idea what this problem might be from? Any info would be greatly appreciated.

Thank you

 

Start with the fuel filter and pump diagnostics. From there, head to ignition. Pull the DTC from the KAM. Auto zone will do it free.

 

How many miles on the truck? How many miles on the plugs, wires, and coil packs? Sounds like it's probably time for a good old-fashioned "tuneup".

A dirty IAC shouldn't trip the CEL - it's most likely ignition-related - but it's time to go through everything.

 

Truck has around 157K on it, plug wires and packs have never been changed to my knowledge, plugs have been changed I believe, I seem to remember when i was deployed my ex having an issue with the truck and having some clown change the plugs which later caused one to blow out while driving down the road, that was around 5years ago so unable to say mileage when that happened.

 

Anyhow heading up to AZ to see what codes are being thrown will be back with the results.

 

OK back from autozone here are the codes that have been thrown:
P0300
P0136
P1131
P0174
P0171
sadly I think I am in the could be this could be that zone! Anyone suggest where to start replacing things?

 

Change the plugs, and use only Motorcraft. Do not use antiseize, and torque them to 28 ft/lb to prevent blowout. Clear the codes and see which ones come back, you probably have more issues than just the plugs.

 

ok heres the latest. I decided to take my truck into the dealer for them to fix the rough idle problem since i am kinda screwed on free time. After they did their tests I received a call from them stating that the think my engine had jumped timing, 4 cylinders were down, the bearings were shot, and said it was not worth fixing and i would probably have to get a new engine at a cost of around 5k. Is this possible? I mean the truck runs great other than at idle at a stop light. With all that supposedly wrong wouldnt it run like total crap all the time?

 

Iduno, that doesn't sound right. Did you take it to Ford?

 

Take it to another dealer. Your being screwed.

 

Was it knocking? If not, how in the world did they come to the conclusion that the
bearings were shot? If you had four cylinders down, I seriously doubt you could even drive it.

 

Maybe they meant 4 cylinders were down on compression ? Hard to say, but that's how it would stay running. If that's the case and the compression test was done right, -I would conclude the same.

But yea, get a second opinion. See if you can get the compression numbers so that you can compare the second opinion with the first. You know? That would more less confirm.