Q: my car is rumbling at idle

It depends on the origin of the noise and/or problem. If the rumbling is due, say, to an exhaust leak and the leak is, say, in the exhaust manifold you risk carbon monoxide poisoning by driving the car. If the rumbling is accompanied by solid (NOT blinding) illumination of the check engine light and at, say 1,200 RPM on up the engine is running reasonably smoothly, typically it will be OK to drive. The "rougher" the operation of the engine, the more likely you have a misfiring condition which could damage the catalytic converter. But, there are so many possibilities: a worrisome one would be, for example, if the timing belt has slipped. If you are in a locale served by YourMechanic’s network of certified mechanics, you can get a quick answer by just setting up a mobile diagnostic and the mechanic will come right to your location. The bottom line is health first, so if the noise is not due to an exhaust leak, is only in evidence at idle, the vehicle has sufficient oil and coolant, air in the tires, is NOT overheating, typically you can still drive the car for a "while", how long just depends on exactly what is causing the fault which leads me to the final bit of advice which is, plan your route, that is make your decision assuming that the car "could" break down and leave you stranded. So, don’t drive through a hot desert in the middle of the day. Once you arrive safely home, you should request a rough engine idle diagnostic and a certified Mechanic will get this resolved for you promptly. Let us know if you have any other questions or concerns.