Rough Idle and hesitation at around 50mph.

[Rob_E]

Ok, so I've scoured this forum and I just can't figure it out.

I'm a very amateur diy mechanic, but I tend to be able to figure things out pretty easily (i.e. I've never had to get anything towed after trying to fix it).

After my 02 4.6 mounty warms up, it idles roughly when stopping at a light around 600rpm, and I'm getting some hesitation intermittently around 50mph.

I've done the following in the last week with a few days between each:

Plugs - Autolite platinum
Fuel Filter (well overdue) - Purolator
Air Filter - STP and cleaned MAF sensor. That was this afternoon.

I disconnected the battery to reset the code today. Ran it about 5 miles at low and high speed, but still the same problem. It hasn't thrown a code after the reset, but I assume it will. Autozone read it but it was just generic (1151... I think. I can't remember).

None have these have improved anything very much, besides the normal improvements of changing each of these things out. I'm still also only showing around 13mpg and she's still running rough.

Oh, and it's not dry rotted vacuum hose problem. I fixed that (for $8 thanks to this awesome forum) about 6 months ago.

I suppose the PCV would be the next step, although I'm not sure where it's located. I can't find much about it on this site.

Any ideas would be greatly appreciated. She has about 117k miles on her. I've also been running Techron for 2 tanks, and I put a treatment of Lucas through on the last one.

 

[GottaBigBlock]

having the same issues. please let me know If you find anything....I also checked for vacumn leaks(none) in addition to everything you've done. This is exactly what my Mountaineer is doing. Going to the dealer after the pcv monday. the pcv is a dealer only item, they screw in under air intake on passenger valve cover, not sure is fitting on drivers side is valve or just a fitting( I assume it's just a fitting).

 

[Rob_E]

My issue just ended up being the O2 sensor. Took it to my mechanic and when they put it on the computer the left bank was working intermittently. Replaced it and all has been well for a few months. I'm kinda glad I tried everything else first since all that stuff needed replacing anyway according to the mileage.


I think it cost me around $200 with labor. Good luck to ya!

EDIT: The PCV took me all of 30 seconds. Beware though. Autozone had the wrong part listed for mine. And the wrong part actually does fit. I can't exactly recall, but there are two valves around the same area. Only one is the PCV valve. The other doesn't have anything clicking around in it. It's just a piece of plastic, which is what they sold me originally. If they try to sell you something that's like $2, chances are it's the wrong part. The correct PCV was around $10 and change. Sorry for being vague. It was a few months ago. Search on here though -- it guided me to the right part.

 

[pipewelder74]

You mentioned the fuel filter was "well overdue"...possibly dirty injectors?
Just a thought.