Motor is stuttering when coasting uphill

[dylanborns]

2001 Escape, V6, 122k miles. I've been having an issue with the rear, downstream O2 sensor for the past few weeks. I would get the check engine light and the code "P0136" and "Cylinder 4 misfire". Along with the Chk engine light being on, I also had a pretty rough "stuttering" at different times while driving. With my very basic knowledge on how to work on cars, I thought maybe the misfire that the code was reading was also the stuttering I was feeling, and that it maybe all caused by the bad O2 sensor readings.
I replaced the sensor, and decided at that time that I really needed to do a tune up since it was 22K miles overdue.
I replaced all 6 spark plugs, and decided that since I have the top of the motor off, I should replace the back 3 coil packs so I don't have to do it in the near future. I did that and will replace the front 3 coil packs soon. I also plan on changing the other 3 O2 sensors.
Driving it the last few days, I've noticed that stuttering is still there. I really paid attention to when it was happening, and it seems to be only when I'm coasting, not giving it gas, and I come upon an incline. It then stutters pretty bad until I give it some gas. It then powers past it and drives smooth.
Anytime I feel it happening, I just give a little gas and its fine.
Any ideas on what the problem could be?
-If I was having a misfire on cylinder 4 like the code was reading in my initial problem with the O2 sensor, wouldn't that still be showing up with a check engine light blinking? There's no light coming on anymore.
-Would I even be able to feel a misfire like a stuttering if it was happening?
Thanks for any suggestions!

[65comet]

I had similar symptoms in my 02' V6. Same code except on number 2. The exhaust manifolds have a small catalytic converter built into them. They like to go bad and send their guts back into the main large cat, plugging it up. Some "wise" engineer thought it would be helpful to have these extra cats to warm up faster than the main and reduce emissions faster. I just replaced the main and left the manifolds alone. Codes went away, Escape ran great and it has passed every emissions test since then. There are threads on how to test if your catalytic converter is clogged, so I'd suggest giving them a search. The real indicator was the super high back pressure feeding up into the EGR valve.
Here are a couple of threads.
http://www.automotiveforums.com/vbul...ight=catalytic
http://www.automotiveforums.com/vbul...ight=catalytic
http://www.automotiveforums.com/vbul...ight=catalytic

[dylanborns]

Thanks for the info and links. I checked them out, and it seems like most people with cat problems are saying they are loosing power on incline; I'm not loosing power, it just "stutters" a few times until I give it a little gas. I'm probably not explaining it very good, but its like its fine until it gets to a certain rpm, then will jerk until you put some gas to it. I don't feel like I'm losing any power though.
I like the idea of testing with a vacuum gauge, it gives me a chance to buy a new tool. I'll have to google how to do that though.
Thanks

[dylanborns]

Update: I replaced coils #4,5,6 today and took it for the 10 mile drive to reset the PCM. It didn't have any stuttering issues, and didn't sound like it was going to die at red lights. I'm thinking that it was a problem with cylinder #4, like my initial code was showing "cylinder 4 misfire" with the O2 sensor code. I'll drive it some more tomorrow and hopefully the problem is solved.