I recently bought an '03 Suburban LT, 5.3L V8, with about 180k miles. I initially had an issue with sluggish acceleration that seems to have been fixed when I cleaned the ground connections under the driver door. But yesterday and today when I sat idling for a while it started to idle rough. Then today when I got driving again it had almost no power and had intermittent popping/thumping sound from the engine. The engine light came on so I immediately stopped and turned off the engine. After a few minutes I started it again and there was no engine light but a low coolant level alert, even though coolant level looks okay (about 2" in the reservoir) and oil temp was fine, center of the gauge. I had it towed 6 miles home to be safe and when I threw the OBD2 scanner on it, it didn't read any codes.

Additional things to consider: today and yesterday are the first really hot days we've had since I bought the truck. Also I can't imagine it's related but before this happened I had the issue where the driver's vents are blowing hot while everything else is blowing cold ac air. I was trying to cycle the damper by cranking cabin temp high and low when I started noticing the rough idle.

My initial guess for the popping/rough idle is bad connection on one of the spark plugs (bad wire or connection) but I'm totally new to this so I'm totally open to ideas.

As for the codes, I thought they were supposed to be stored for a while, so why didn't my reader see anything? Is that just newer trucks that do that?

Sorry for the long post. I appreciate any advice!