cold idle slump until warm

I'm sure this has been covered a dozen times before, but now that it's cold again...

My 1991 C1500 4.3L cold idles (when started for the first time in the morning or after sitting a long time) high and fine, but when I put it into drive or reverse, it drops to almost a point of killing if i don't give it any gas. It does not kill, but takes a moment or two to get back up to proper idle. Once it's warm, everything is fine with no issues.

any ideas?

no ideas from anyone about this?

Sounds like the Idle Air Control Valve is sticking, try cleaning or just replace it. Should be able to pick one up and any parts store.

The fact that it runs fine warm might indicate a coolant temperature sensor problem.

do you have to drain the entire coolant system to replace the coolant temp sensor since its in the side of the block?

There are several ways to check it first, rather than just replace it. If you don't have a scan tool, you can check the resistance with a multimeter. I don't have the numbers in front of me, but can get them. Basically, what you're looking for is a change in resistance between a cold engine and a warm engine. Take the plug off when the engine's cold, and take a reading. Then, when the engine is warmed up, take the connector off again, and take another reading. Post the readings on here. If I don't have the numbers by then, someone else may have them. From what I recall, with the scan tool, the sensor reads -40 when cold.

i was going to test it the other day with my meter before i saw your post, but did not have time. I was noticing though that the only "switch" I see on mine is the a single lead "switch" coming out of the block on the driver side just above the exhaust manifold. Isn't there a difference between a temperature "sensor" and a temperature "switch"?

I thought the "temp sensor" was the one with two leads (signal and ground) and the "temp switch" is the single lead mounted by my manifold. I do not see the traditional "sensor" mounted near the thermostat area, only the single lead "switch" on the side of the block. How do I deal with that if I only have the single lead "switch" and no dual lead "sensor".

i was going to test it the other day with my meter before i saw your post, but did not have time. I was noticing though that the only "switch" I see on mine is the a single lead "switch" coming out of the block on the driver side just above the exhaust manifold. Isn't there a difference between a temperature "sensor" and a temperature "switch"?

I thought the "temp sensor" was the one with two leads (signal and ground) and the "temp switch" is the single lead mounted by my manifold. I do not see the traditional "sensor" mounted near the thermostat area, only the single lead "switch" on the side of the block. How do I deal with that if I only have the single lead "switch" and no dual lead "sensor".

The single wire "switch" in the cylinder head is for the guage. You should have a 2 wire sensor somewhere on the intake manifold which tells the ECM the engine temp.

//2000CAYukon

I have a 4.3 Vortec in my Astro. I also have the temperature sensor mounted between the plugs on the drivers side. Manual indicates this sensor is used for the gage and the ECM. If you have a gage that indicates normal operating temperature, approx 195 degrees, the sensor is probably good. I have seen the 2 wire sensors mounted by the thermostat in the 5.0 and 5.7 V8 emgines.