I have a 2002 Bonneville and my heaT blows luke warm air not hot .. it will heat up if driving and go on thruway but not when just sitting and running any suggestions????
Check the coolant level. If it's low, not enough coolant can circulate to the heater core. You can also check the heater hoses when the engine is running and up to temperature, squeeze them and see if they are hot and feel pressurized. If not coolant is not flowing to the core, which indicates either low coolant levels, a bad thermostat not opening, or a failing water pump. Based on your description though, my bet is on a bad water pump.
Search Pontiac Bonneville Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Pontiac Bonneville Experts