I'd be suspicious of the thermostat.
When a vehicle is idling, the engine may not produce enough heat to warm the coolant effectively, leading to cold air from the heater. In contrast, while driving, the engine works harder and generates more heat, allowing the heater to blow warm air. The engine temperature can rise while idling due to reduced airflow through the radiator and less coolant circulation, while driving increases airflow and coolant flow, helping to cool the engine.
Irratic idling condition is indication of intake/inlet manifold gasket leak. Change gasket immediately. This particularly applies to EFI engines. Newaz.
need to replace the intake manifold gasket
As the vehicle sits idling the driveshaft is not rotating.
Yes, when idling and driving.
Probably wheel bearings or wheels are unbalanced
It depends on how long you are idling, or how fast you are going. If you know you are going to be idling for a long time, it's best just to put your car in park.
Car emissions can be reduced by reducing idling time and by driving at a moderate highway speed when possible. Driving too fast and idling are both wasteful in terms of fuel, and increase the vehicle's emissions.
It's a 1997 Tahoe
I am have the same problem with my 06 Monte Carlo LT. Took to the dealer. Its a head gasket leak.
You need to check the operation of the radiator fan.
2001 sienna stall while just stop while driving. electric just cut out power, then switch can operated but idling roughling