Rough idle at start, shuts off in gear...

I've had this issue before, but like the first time, can't figure it out.

1992 S10 Blazer, 4.3L, 4x4, TBI "Z"

When I start the truck, it idles rough, like it's idling too low, and even feels like it's missing during idle. Sometimes when I put it in gear (reverse or drive), it shuts off. No codes are being thrown. It has no problems driving around town or on the highway. It's just that initial start and idle.

I've checked all the following with a shop manual:
Ignition Control Mod.- Orig and 2nd one from junk yard. Both tested good at store. Even the testing in the shop manual with an ohm meter and battery tested good.
Ignition coil- tested good using shop manual testing
TPS- Scan shows .2-.7 at idle.
Plugs, wires, cap, and rotor are good.
Vacuum is good.
Haven't checked IAC, EGR

I recently moved cross country, and about halfway through, I broke down. Engine would turn over, fuel relay would click, injectors would work, but no fuel. Pulled it in to a truck shop, and after all my testing and theirs, we determined it was the fuel pump. After they had to fix a pinched hose, it ran. I made it to Texas. I didn't have the idle issues prior to the trip. Just had the tranny rebuilt and everything was great.

I thought, at first, the ignition control mod was the problem because it got a bit warm pulling the trailer, and I know those things don't like too much heat. No dice.

So, what controls idle at Park and in gear but at idle? EGR, IAC?

I did a WinALDL scan. IAC at Park/Idle ranges from 18-55. The engine never runs in Open Loop. I would say the engine runs mostly rich according to the scan. I've attached a manageable version of the WinALDL data. If you can use that data, please do.

Also, I need to check the thermostat or temp sensor. Scan reads the engine never getting higher than 180.

Thanks

I've had this issue before, but like the first time, can't figure it out.

1992 S10 Blazer, 4.3L, 4x4, TBI "Z"

When I start the truck, it idles rough, like it's idling too low, and even feels like it's missing during idle. Sometimes when I put it in gear (reverse or drive), it shuts off. No codes are being thrown. It has no problems driving around town or on the highway. It's just that initial start and idle.

I've checked all the following with a shop manual:
Ignition Control Mod.- Orig and 2nd one from junk yard. Both tested good at store. Even the testing in the shop manual with an ohm meter and battery tested good.
Ignition coil- tested good using shop manual testing
TPS- Scan shows .2-.7 at idle.
Plugs, wires, cap, and rotor are good.
Vacuum is good.
Haven't checked IAC, EGR

I recently moved cross country, and about halfway through, I broke down. Engine would turn over, fuel relay would click, injectors would work, but no fuel. Pulled it in to a truck shop, and after all my testing and theirs, we determined it was the fuel pump. After they had to fix a pinched hose, it ran. I made it to Texas. I didn't have the idle issues prior to the trip. Just had the tranny rebuilt and everything was great.

I thought, at first, the ignition control mod was the problem because it got a bit warm pulling the trailer, and I know those things don't like too much heat. No dice.

So, what controls idle at Park and in gear but at idle? EGR, IAC?

I did a WinALDL scan. IAC at Park/Idle ranges from 18-55. The engine never runs in Open Loop. I would say the engine runs mostly rich according to the scan. I've attached a manageable version of the WinALDL data. If you can use that data, please do.

Also, I need to check the thermostat or temp sensor. Scan reads the engine never getting higher than 180.

Thanks

Check IAC and EGR valve and for any vacuum leaks.

What are the best ways to check those??

What are the best ways to check those??

IAC Valve control needs to be checked with a engine capable canner.
EGR valve can be checked by plugging exhaust and intake holes under egr valve.

After driving it for a while, I determined it was a computer learning problem. I had recently disconnected the battery to clear a code. I think from now on, as long as the SES light isn't on, I will leave them in the computer.