Pontiac 6000le V-6 heat troubles

[automan63]

I have 1990 pontiac 6000le.Has the 3.1 v-6 engine.Have checked the radiator and coolant level is full.Replaced the thermostat recently also.Doesnt have any leaks in the coolant system.Wondering if I have a bad heater core and the symptoms would be?Also where is it?If not the heater core what else may be causing the problem?Is somekind of sensor causing this problem?

Also car has a very low idle speed after the cold stepdown idle mode.I have replace a sensor I thought controls this.Is there a setting or something that I can change?Also is there timing belt on this engine and a way to check the timing?Car just doesnt have the power it use to have and runs very rough after it has heated up.Engine has 155.550 miles on it.

Help Please Aaron

[Roger]

There are many possibilities some you can check but if you have a vacuum control problem you may be in for a trip to the shop. To test your heater core locate the inlet hose and the outlet hose where they enter the firewall. While your car is at operating temperature and heater on max heat feel these hoses both should be hot to the touch. If inlet hose is cold then problem exists before the heater core. If outlet hose is cold then problem could be heater core blockage, bad control valve,or a vacuum problem causing mixing blender to be inop. The control valve is vacuum actuated and when heat is asked for, vacuum opens this valve allowing water flow to the heater core. Remove the vacuum line from the back of this valve and put your finger over the line and see if vacuum is present. The valve is located just before inlet hose enters the firewall. If Both hoses are hot then you have a problem with vacuum control at the selector switch, this is generally a troubleshooting chore for a qualified mechanic as vacuum pump and other test equipment is needed.