I don't know what the "heat" has to do with it, but a faulty cruise control is the sign of a bad throttle actuator, which could be putting your car in limp mode.
The throttle actuators have potentiometers that wear out over time, but more likely in your case, the insulation on the wiring harness on the throttle actuator itself suffers from the same degradation problem as that of your engine wiring harness.
This is a systemic problem on all M104 engined cars from 1993-1995.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".