Explaining Cold Starting Problems

By Brian Klaubert

Soon the mornings will be getting colder. With the onset of cooler weather, some vehicles will become harder to start. Many people will experience this in either of two ways. Either the engine will spin over for a longer period of time before starting, or the engine will stall immediately after starting. In advanced cases, you may need to feather the gas pedal to keep the engine running for a few minutes until it warms up.

The possible causes for this common problem vary by manufacturer. However, a common cause across all manufacturers is a dirty upper air induction, or air intake, system. On many engines, oil vapor from inside the engine is ducted directly to this upper air intake. The oil vapors plate the sides of the air system. A gummy deposit will form in a ring around the “throttle plate”. This will hamper the ability of the computer to maintain an adequate idle speed. A common corrective and preventative measure is to have an upper air induction cleaning performed. This service costs about $120.

As a corrective service, you will need to get this done at a full service repair facility or dealership. Many quick lube centers offer a less expensive variation of the upper intake cleaning. To minimize their risk of damaging expensive sensors, and to speed up the process, they usually administer the cleaner at the bottom of the intake manifold. This leaves the “cold start” problem area un-cleaned.

Another common source of problems is a computerized device that is responsible for controlling engine idle speed. The device is called an Idle Air Control valve or motor. These electronic devices can become fouled with carbon, gummy deposits, or simply fail. On many vehicles, the parts and labor cost for this device is around $150.

Carbon deposits on the top of the intake valves can cause cold starting problems. It takes very little gasoline to keep each individual cylinder running. The gas is finely atomized by the fuel injector. The carbon deposit can initially absorb a sufficient quantity of atomized gasoline to affect the idle speed of the engine. The vehicle computer is programmed to start cold at a specific fuel rate. After a short period of running, the computer and its sensors take over. They quickly compensate for the fuel/air ratio and the idle smoothes out. The Air Induction cleaning, mentioned above, also cleans these deposits from the tops of the valves.

Some vehicles are prone to developing a vacuum leak at the intake manifold to cylinder head gasket. This is very vehicle specific. The vehicles most prone to this have a plastic intake manifold and O-ring type gaskets. These vehicles will run terrible until they are warmed up, then the computer compensates for the leak. Usually the Check Engine Light will also be on.

To conclude, cold weather also takes its toll on batteries. A problem with the battery will result in the engine not spinning at all. Sometimes you will hear a clicking noise when the key is turned, other times there is only silence. Many service facilities offer a free battery check. You may ask for this at your next oil change, or just come in specifically for it. The average useful life of a battery is about 3-4 years.

Brian Klaubert owns Christian Brothers Automotive – Hamilton Mill, on Hwy 124 in Dacula, winner of Gwinnett’s Choice for Auto Repair.