[Part throttle hesitation]

I decided to use justanswer.com and the Subaru tech suggested I replace the front o2 sensor that sits above the point where the two exhaust manifolds come down. It was $60 at Napa and the problems are gone. Hopefully they won return but just for fun if the egr is a cheap part I can just replace that, too.

[Part throttle hesitation]

I ran a can of gm top engine clean through the IAC in case it was somehow gunked up, alas, no improvement. I also put some gm injector cleaner in the tank, filled it up, i suppose i'll have to wait but theres no improvement with that yet.

 

Damn, this is frustrating. Does anyone have any idea what i'm talking about? Am i asking the right questions? How about how do i know if this is the ignition system or the fuel system?

 

I have the same problem on my 01 Outback - I've been watching your post and similar posts at subaruoutback.org. There are a few posts that have said they replaced the TPS sensor and everything was magically fixed. I've replaced it twice with no change. I've run the stuff through the fuel tank, checked for vacuum leaks, and that's about it. I haven't checked really anything else under the assumption that if I watch the posts long enough someone will come up with an answer.

 

I posted at the other forum my experience driving to the mountains - I don't know if this will give you any other ideas - I live in Colorado Springs and go snowboarding in the mountains. I have to drive down about 1k feet to Denver (from about 6300 ft to 5280 ft) then I have to climb to 12-13k feet once I leave Denver headed west. The car did it's same behavior - bucking, hesitating, etc on the way to Denver but it wasn't any worse than "normal".

 

The minute I started the climb into the mountains (you turn a corner on the interstate and then it's just a straight climb up), the car started bucking, hesitating, losing power, etc like I turned a switch. I endured it for the next hour and a half as it repeated the behavior every few seconds. I was ready to throw it off a cliff.

 

I finally made it there.

 

When I turned for home in the evening, it drove flawlessly all the way down the mountains and back to my house. If there were any hesitations it wasn't any worse than "normal".

 

Like I said on the other forum, the problem increased greatly when climbing straight up into the mountains. That's why I don't think its something like spark plugs or fuel quality or fuel filters, or plug wires, etc - the problem would have repeated itself at the same rpm either up into the mountains or headed down.

 

I don't think we can blame it on air pressure because it went bananas within a few moments of climbing straight up. The air pressure wouldn't have changed that much in that short of time. I am not the mechanic you are - but maybe this is helpful info?