I have a 99 blazer, I have recently hit 115K miles. The tranny has been serviced, the fuel pump and filter were just replaced. A couple of days ago I was driving and I noticed whenever I came to a stop at a light or stop sign my car would be kind of rough. It sounds like my engine is being choked just a little and the RPM's drop about 100. It does not do this if I come to a complete stop and put it in park. I also noticed that when it does this there is a soft clicking sound and my temp gauge will not get over 155-ish. I was driving for about an hour when I noticed this and no matter what my temp stalled at 155 and would not come up. I am not to sure where to start looking for. Oh also, at low speeds it is kind of sluggish to accelerate, but that is usually just after the car was started and is still cold.

EDIT: Sorry, just noticed I accidentally clicked 1st Gen. If a mod could move this I would appreciate it.

 

*Moved to 2nd Gen Tech*

155F is way too low. The PCM will be in open loop mode where it will push more fuel into the engine than is really required in attempt to increase engine temperature. It sounds like your thermostat is stuck open not allowing the engine to come up to temperature. Too much fuel can end up fouling spark plugs and clogging catalytic converters so I would definitely get that looked at as soon as possible.

 

I was thinking it was the thermostat and was going to pull it to test it today but was wondering if anyone had any other ideas, I will definitely get that checked today, thank you.

 

I'd just plan on getting a stant replacement t-stat and be done with it. They're cheap enough. Replace the radiator cap at the same time with a stant safe-t-cap. Money well spent!