Help ID sputter/rough idle

[WestcliffeLX470]

Hi guys,
1999 LX 470 with 128k. Did the timing belt, water pump, TB clean, MAF clean, new air filter, and spark plugs about 500 miles ago and it ran fine for several weeks. Was up in the mountains this weekend and noticed the engine was missing/sputtering at all speeds but over 55mph or so and generally running rough. Sputters at idle but doesn't die. Seemed like a classic case of a coil pack gone wrong but doesn't have a check engine light or throw any codes. I figured if I had screwed up the plugs that I would be getting a code...

Any ideas? Should I wait a couple days to see if a code develops? I was wondering if it could be linked to a fuel issue. Its on its 2nd tank of fuel since the problem surfaced so I don't think it was bad gas (I always use premium). Will it take a while for the ECU to throw a code? Am I experiencing "limp home" mode?

I am wracking my brain to think if any of my recent diy preventative maintenance could have caused this but it ran like a champ for several weeks before this randomly started happening.

Help kind sirs!

 

[WestcliffeLX470]

I just opened up the most accessible timing belt cover (passenger side) and the belt is dry and seems nice and tight with plenty of tension - no oil or coolant which would make it skip teeth and throw off the timing. Anybody had the belt jump teeth and screw up the timing? I don't have the heart to tear it all down just yet to check the timing. Any way to cheat and check the timing with a light?