Idle fluctuate s

The computer enriches the fuel mixture and then leans it out to see fluctuation and changes at the oxygen sensor readings, these changes forth and back can often be noticed, also AC pumps cycle from time to time for short bursts just to keep them freed up i think. when the AC clutch kicks in the idle will also fluctuate, again it is normal to some degree. As for air pockets fill the cooling system there should be no air pockets at all nothing but coolant. Air does a poor job of drawing heat from the engine from the inside of a cooling system however it works well outside the cooling system.

Temp gauge fluctuates? From around 200 degrees and up, then back down? This is an air pocket. First check the reservoir for leaks, then check the hose from the reservoir to the radiator for leaks and if it is kinked. No kinks in this hose is important. When I purge these systems, I drive it till hot, then turn sharp circles both ways. In a parking lot. This seems to help purge the heater core. Then refill as necessary. I do this with any car that has the 3.4 or 3.1 engine.

Sounds like there is still air pockets in the coolant system, let idle to full temp with the cap off and the car on an upword angle to alow air to move then while engine running and coolant if needed to hot mark on the coolant tank.

could be a air pockets in the coolant system that have top bled out
it is a simple exercise to have a compression test done to check for head gasket or cracked head

I had a similar problem. Replaced head gasket, but low coolant light stayed on. My problem was air in the system. A flush and fill kit may work, however, I had a local shop do a "flush and fill" and the problem remained. What I did... With vehicle running, and radiator cap off, bring engine to operating temperature. Increase rpms slightly above idle until coolant can be seen moving in radiator (thermostat open). Add small amounts of coolant, keeping the radiator level just below overflow hole in cap area. In my case, after about 15 minutes at slightly above idle rpms, a large pocket of air escaped. I topped off radiator, installed cap, and let engine cool. Problem has not returned in last six months. *Note coolant is VERY HOT, and if rpms fluctuate, coolant will expel quickly from radiator. Also, when the air pocket escaped, coolant also sprays out. Use caution to avoid being burned.

Chevy made some weak intake gaskets on 3.1 and 3.4. My guess is that the intake gasket is weak and/or leaking and it is letting pressure out somewhere. At idle maybe the system pressure is to little to push hot coolant into the heater core.

Many cars have a bleeder valve to let out air pocket from the cooling system. Fill the radiator, with the cap off, let it idle at about 1500-2000 rpm's until it reaches normal operating temp. on the gauge, then the thermostat will open allowing the coolant to circulate throughout the engine and radiator. any air will then be gone after about 10 minutes at a fast idle. Top off the coolant, replace cap and recheck the level after a short drive of a few miles and has time to cool.
If there is enough trapped air in the system, you will have no heat. The heater box loves to trap a lot of air in it as its like a tiny radiator itself.

Loose Radiator or coolant cap in cold and have the car idle for five minutes with out the cap, or have the car idle for 10 minutes, wile running remove cap, let air pressure out and put cap back, do it 3 or 4 times till all air is out...

If this car is remote start GM has a service bulletin out to do a computer flash to correct this problem, it will probably blow hot air in the summer if it remote started if you don't have the computer flash done. Hope this helps

You most likely have an air pocket in the cooling system. The heater core on these vans is much higher than the engine and they can be tough to get all the air out of them.

Make sure the coolant in the radiator is full when engine is cold- also fill the overflow bottle to the top. Chock the rear wheels. Jack up the front of the van as far as you can and support with jack stands. Run the engine until it's warm and then hold the RPMS at 2000 for about 5 minutes while checking for heat inside the cabin. You may hear some funny noises like something is trying to come through the firewall forcefully! That's the air pocket moving... you might not hear this also. Once you have good heat inside, let the engine idle- if the air coming form the vents cools off after a couple minutes, the air is still there- keep doing this until the air is hot coming from the vents at idle for more than a couple minutes. Once you have good heat, turn the engine off and let the engine cool completely- at least a couple hours... you will most likely see the level in the overflow drop dramatically. Lower vehicle and make sure overflow is at COLD FULL mark.

Newer Altimas also had a similar situation in which heat would go away at idle- usually not a problem with an air pocket, but Nissan has a bulletin out on putting the correct concentration of coolant/water in the system- these cars are very sensitive to changes in coolant mixture concentration.

Nissan Scope Technician- 10 years with Nissan