Here’s a real doozy. My 99 Blazer is running extremely rough, especially in the morning or in damp conditions. There are absolutely no check engine lights and all gauges read good. So far on top of dry gas and injector cleaners, I have changed all filters, including fuel and air, the sparkplugs, wires, pcv valve, distributer cap and rotor. Does anyone have any suggestions. It really amazes me that for as rough as this thing rides, it makes no indication on my gauges. Just to see if maybe the check engine light was blown out, I still had it hooked up to the computer and there were no codes. On a side note, in the past I had heard a girgling sound on the passenger side of my engine, but I figured that was just my A/C that I haven’t had in 3 years.
The EGR valves on these engines were problematic,check yours out. Don’t let the absence of a EGR code keep you from looking at it.