How do i change the intake manifold gasket

Does the engine cooling fan work as designed?

Coolant leaks,When the intake manifold gasket cracks or blows out, coolant will leak out of the intake manifold. You may see puddles underneath your car or notice smoke or steam coming off of the engine and exhaust from the coolant dripping onto it and then burning.Overheating, If the intake manifold gasket fails and allows coolant to leak out into the engine, your car will begin to overheat. If your car frequently runs low on coolant or begins to overheat, check the intake manifold gasket.Running poorly, When the intake manifold gasket falters, it affects the way the motor handles its emission gases. The change in pressure can affect the vacuum in the intake as well as how smoothly your car runs. Mainly, it will idle roughly and may hesitate, cough or sputter.

Have you replaced the intake manifold gaskets? These engines have a history of leaking intake manifold gaskets. Water leaks into the intake and is burned off in the cylinders. If the engine overheats enough times, you will eventually blow the head gaskets.

Start by performing a compression check to make sure you haven't blown the head gaskets. Then make sure the car is really overheating (i.e. check the temperature of the engine with a infrared thermometer (they are cheap at Harbor Freight).

If it is really overheating, and you've really changed everything else, you need to change the intake manifold gaskets. Be sure to get the improved gaskets from the parts store (they have a metal core with rubber coating).

swap the injector with another cylinder and see if the misfire follows the injector or start with a compression test

Is it losing it out on the ground? Could be head gaskets or intake manifold gaskets have failed.

it is 100% intake gasket,if you check the coolant reservoir,and there is oil in it,if it was head gasket you had white smoke out of tail pipe and loss of power
you can run run the cylinder compression test,

gm used crappy plastic intake manifold gasket,
unfortunately, it is about 1000$ or so fix

From what your describing it sounds like a blown intake gasket, the gasket itself costs under $30 if you are doing this yourself. Be sure to get the manifold gasket and not the plenum gasket too

A lot of GM V-6's had problems with poor intake manifold gaskets. Any moisture around the oil cap? Or anti freeze in the oil?

This is basicly a very time consuming job rather than a physically hard one to complete. In order to replace the gasket you must remove the intake plenum,throttle body, and misc. vacuum hoses. The wiring harness connections must also be disconnected. Finally the intake manifold is exposed. The bolts holding the manifold to the block are removed exposing the leaking gasket. After removing the push rods and placing them in the correct order to be replaced the gasket and sealants can be removed. Finally replace everything in reverse order. Be sure to consult a GM manual for correct bolt torch specs. The correct specs for the manifold bolts usually come with the gasket. Make sure to change your oil a few times after this job in case any coolant entered the block. Also,change the thermostat and the oil seal on the distributor half shaft cap while you have everything off. Good Luck

Obviously your engine overheats and damages the cylinder head gasket , When mixing engine oil with the coolant, it looks like chocolate.