My car runs-on. I need a solenoid

The MYTH is: If your car runs-on, you need an idle solenoid. This is jumping the gun; too soon a presumption. First, a look at what and why engines run-on: WHAT IS IT:

Engine “run-on” is where you turn the key off and the engine still combusts or would run and cough a little more. Some extreme examples have the engine roughly continuously idling until you release the clutch in gear to force the engine to stall. As the run-on is uncontrolled, some may reverse the engine rotation and violently force the intake charge back out through the carburettor.

WHY IS THIS HAPPENING: The cause of engine run-on is NOT the carburettor: As you turn your key off, you are cutting off the electric current to the spark plugs. If there is something glowing hot enough in the cylinder chambers, it will ignite the fuel. Also, if the compression is so high, it may detonate the air-fuel charge (dieseling). Or a combination of both. Common issues being carbon build up in the chambers and valves edges wearing thin to glow red hot. A couple of instances found the spark plugs too hot and changing to a colder plug fixed it.

SOLUTIONS: In our workshop, most run-on is resolved with fine tuning: Run the car until fully warmed up and choke is off. Check the ignition timing is set 4 to 5 degrees above the factory setting (with the vac hose dis-connected), reconnect the vac hose.

Set idle speed screw to a low but stable speed (typical 4cyl = 700 to 800RPM) turn the idle mixture screw slowly in or out to archive the highest idle(indicating the strongest mixture), reset the idle speed screw.

Now slowly turn the idle mixture screw in until you hear ANY change in speed or quality (indicating just too lean), back-out the mixture screw a little. You now have the idle set at best-lean position.

(Note- setting idle mixture, and all general tune-up procedures are best done after oil change. Idle mixture should be reset after each oil change.

Test drive the car and switch off to check for run-on. If there is still run-on, you may need a new idle solenoid.