Okay, so I thought I had it solved before, but that only lasted 2 days. I know there's a lot folks out there with hesitation/stumbling problems, so maybe this will help someone.

You know the drill, low RPM stumbling under 2K, and then it just takes off. In my case, not temp related...happens in morning and nights. It all started after installing the Random Tech y-pipe.

So first changed wires to OTVC to avoid headers...had 90K on the stock ones, good thing to do regardless. Didn't fix it.

Next changed fuel filter...ran a little better, but stumbling still there.

Scanned it and cylinder #3 was misfiring consistently. Checked the plug..looked fine. Since just cylinder #3 and saw some leaking from the waterpump, so changed the opti. Ran great for 2 days...thought I had solved the stumbling issue. Woo hoo...and then it came back. I didn't mind changing the opti though, since it did have 90K on the stock one.

Checked EGR valve and leaks, didn't see any issues. The engine shook like crazy at idle and then smoothed out and then shook again.

Okay, so that's enough $$ and parts thrown at it. Went to scan it again, and now showed slow switching bank1 front O2....and about 1000 misfires at cylinder 5 and 7. Also the voltage from bank1 and bank2 were way off from each other. I couldn't believe it was the O2s, because they only had 3K miles on them. But that's the only code that showed up.

This time checked for leaks again and WOW....my front header bolt on the cylinder 1 port was about 1/2" out. I didn't know header bolts could back out..but trust me they can. So I guess all that shaking at idle and stumbling shook the bolt out and problem got worse because the leak was getting bigger. Good thing the SLPs have 3/8" flanges.

Changed the bank1 front O2 last week and it's been running with no problems. Scanned it again today, NO misfires and both front O2 are active...flopping from 100mv to 900mv, as expected. I guess somewhere in the process of installing the y-pipe I must have damaged the O2.

After a week of driving and no codes or misfires, I'm going to claim success.

So, lesson of the day: SCAN YOUR CAR. Forget throwing parts at it, grab a buddy with a scanner and sit down and SCAN YOUR CAR. It will definitely help save time and frustration.