Misfire

What you need then is a scanner with recording capabilities. When the problem occurs, you press the "record" button to record a few seconds of data, then you can play it back slowly later to see what changed. Since the data goes through the scanner's memory, the recording actually starts a few seconds before you pressed the button.

As a general rule, at least on older vehicles, the fuel supply system is not monitored, so with no fault codes, that's a good system to suspect. Spark / ignition problems are usually detected and will set fault codes. Valve timing problems are not intermittent. Sensor problems will be detected if they go out of a specific range, and that won't be limited to coming to a stop.

Another good suspect if your engine uses an EGR valve is a chip of carbon getting stuck in the valve. That will hold the valve open enough for exhaust gas to sneak in. There must never be any exhaust gas getting in at idle speed.

I had another Colorado that was doing that and it ended up needing a new electronic throttle body. It wasn't real expensive, a couple hundred bucks.

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