Since a car engine is complex, start identifying the cause of trouble by checking for strange sounds or smells. Examples of strange sounds are high-pitched squeals, a whistling noise from under the hood and clunks from under the vehicle. Check for smells in the engine and the passenger compartment.
If you hear high-pitched squeals that stop when you turn off the engine, check whether the belt is cracked, frayed or glazed. If it's in good condition, readjust it. If there is a whistling noise from under the hood, check the hoses for signs of vacuum leaks. If the whistling noise is from inside the car, look for leaks in the weatherstripping. If you hear clunking sounds from under the car, inspect the car's hydraulic system and shock absorbers and check for loose parts.
If you detect an odor smelling like burning rubber when you open the hood, check whether one of the hoses is loose and in contact with a hot part of the engine. If you smell something while the hood is still closed, check which of your wheels is hot; its brake shoe or brake pad may be dragging. If you smell exhaust fumes in the passenger compartment, check whether the exhaust pipe is faulty.