cold idle slump until warm

oldchevy · #1 12-05-2005, 03:33 AM

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?

oldchevy · #2 12-09-2005, 03:46 AM

no ideas from anyone about this?

horse482 · #3 12-12-2005, 05:28 PM

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.

roadrunner_70 · #4 12-12-2005, 05:55 PM

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

oldchevy · #5 12-12-2005, 07:01 PM

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

roadrunner_70 · #6 12-13-2005, 03:19 AM

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.

oldchevy · #7 12-14-2005, 03:27 AM

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".

2000CAYukon · #8 12-14-2005, 02:03 PM

Quote:

Originally Posted by oldchevy

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

klt · #9 12-14-2005, 10:08 PM

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.

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