Runs Real Bad....

Lets start at the beginning. Is the check engine light on ?
You have an idle air control valve which could be sticking open or shorted to ground. You should be able to unplug it to test. There also could be a gasket or hose that is opening up and causing a huge vac leak.

gas or diesel ???

there is a very real possibility that you may have a flat lobe on the camshaft. Last time I heard one like this, it almost sounded like a popcorn machine in the intake. sound you don't forget. Also, check for a stretch timing chain. Pull plugs, rotate engine to TDC. Pull dist cap off. Put finger on rotor and have someone rotate engine in opposite direction untill you feel rotor move. Look at how far it goes on the timing tab untill you feel the rotor move. Half of that number is the amount of stretch. 4 or more degrees, change chain.

Hello

I know this is going to sound way to simple, but I would look for a air leak on the intake side. The reason I say this is that your engine runs because the computer feels it knows EVERYTHING about EVERYTHING.. Kind of like *********** N law. Well, when you get a vaccum leak, the computer doesnt know its stupid and raising the idle or POOR idle is one of the effects.

Now I am not at all saying this couldnt me something much more difficult, however VAC leaks are also pretty easy to check. Get yourself a can of SPRAY CARB CLEANER from your local parts store, some times gas stations have it too, wal-marts and places like that have it. Start your truck and SPRAY the CARB CLEANER around places that could have a VAC leak. Like hoses, the intake manifold gaskets and those kinds of things. If your engine suddenly runs REALLY ROUGH or even DIES when you spray a certian spot you know thats where your leak is.

I hope this helps you as much as it helped me

From your description, most likely there is a problem with the Idle Air Control (IAC) valve. Its job is to open at idle to let air in when the throttle is closed. Either it is clogged, or it has gone bad. You will need to remove it and clean it, or replace it. It is bolted to the rear of the intake manifold. When you remove it, try starting the engine with the valve removed so air can get in the intake. If the engine idles ok, you'll know that the IAC was causing the problem.

Another possibility is a leak in the vacuum system. With the engine running, listen closely for any tell-tale hissing sound. Inspect all the vacuum hoses and the air intake duct, and repair as needed.

sounds real easy either a bad idle air control solenoid or more likley a blown throttle body gasket. to test fro a blown gasket, with engine running and cool spray carb cleaner or brake cleaner around base of tb were it bolts to intake. when it hits the bad area, should idle down and be normal for a second or 2. iac is possible,try this first since its so common and let me know

Try replacing the coolant temperature sensor for the injection system.

hey common problem w/the 2000 galant. you may need a mirror to see this, look and or feel where your throttle body mates up to your intake manifold. it has a problem of cracking, when you have an air leak there it will run like **** and usually shut off depending on the severity. this will cause you to get the throttle position malfunction code. if that is the case instead of buying a new or used intake manifold. take the old one off, and you can actually cut it flush and weld about a 2 inch in length tube to repair the crack. well let me know how it goes.

it seem our idle air control is dirty when compressor kick in idle air race up get stuck and all of a sudden come off and and on again that why you fell the idle goes up and down remove plastic cover on top of throttle body buy a can off air intake cleaner start the engine and stray the air intake cleaner inside the throttle body give gas at the same time because engine will whant to stall spra inside untill very clean try it out if engine stall dont worry go inside floor the gas pedal and it will start again it gonna shake its normal hope it5 help you fixya our post thanks pierre if any question dont hesitate

Most likely you have a bad Idle motor which is a small motor mounted on the intake manifold. If the motor can run better with your foot on the gas but dies if removed then it is probably this. This motor is controlled by the OBDII computer which gets it's control signal from the temp sensor which is located either on the radiator or engine block (which could also be bad), if the electric fan (if equipped) turns on then this is not the problem part, but the idle motor is. Another possibility is that you have some bad /cracked vacuum hoses which should be checked for first, before replacing the idle motor.