Why are the rpms very erratic when the engine gets hot?

Answer by  ong1057 (47)

The fuel/air mixture is different at different engine temperature. This is usually adjusted by the ecu. The engine temperature sensor could be defective. The idling air valve IAC could also be defective.

Answer by  midhun (16)

Maximum RPMs of an engine is generally a function of two things: piston stroke and how much you've spent on things like conrods and crankshafts. A long piston stroke makes for small size and easy cooling, but will have a far lower redline (and, hence, specific output) than an engine of similar displacement with a shorter stroke and larger bore.

Answer by  mturk11 (140)

RPMS depend on what gear you are in and how hard the gas pedal is pushed. A hot engine responds faster to the gas pedal making the RPMS erratic.

Answer by  Amber40 (24961)

If your car runs rough when hot then you failing component. Typically heat causes the biggest problems with electrical components.

Answer by  Expert19283 (173)

When the engine has the opportunity to heat up, this causes the rpms to being erratic due to timing being off on the engine. Due to the incorrect timing, the engine doesn't know exactly where to put the rpm's to keep the car running smooth.