How to Set the Idle Up on Vehicles

by Contributing Writer; Updated June 12, 2017

The Vehicles out-drive motor, also called the stern drive, comes in a variety of cubic inch sizes Vehicles different size Vehicles and applications. Many of them have two-barrel carburetors, while larger Vehicles have the four-barrel variety Vehicles extra load and fuel demand. Rochester remains a common brand name carburetor used on Vehicles motors, although other makes and models have seen service on the marine Vehicles. A Vehicles owner, with the help of an assistant, can set his carburetor up Vehicles maximum idle performance by following some simple steps and using a few basic tools.

Under The Hood:

 How to Set the Idle Up on a Mercruiser Boat Engine

Tie the boat to a dock. This procedure should be performed with the engine running and under a load while in the water, so prepare to cast off with enough fuel in the tank and tools on board. Pull back your engine cover. Untwist the knob that holds the plenum case over your engine and pull the case off. You can remove the spark arrestor element, if you wish more clearance to access the carburetor.

Start the engine and note the operation of the choke valve in the top of the carburetor throat. It should be fully closed, and then begin to open as the engine warms up. If it does not open all the way, use a screwdriver to loosen the three ring screws that hold the choke dial in place.

Turn the dial counterclockwise to fully open the choke valve, but only a very small turn on the dial. If the choke valve was not fully closed, turn the dial clockwise to close it. Tighten the three ring screws. Shut the engine off. Hook one lead of a tachometer to the negative (-) lead on the ignition coil and the other lead up to a ground source on the engine or frame.

Start the engine and note the rpm on the gauge. Locate the two idle mixture screws that protrude from the carburetor base plate. Refer to your owner's manual for their location. Place a flex-handle carburetor adjusting tool on one of the idle mixture screws. Cast off and have an assistant place the shifter in forward gear at idle speed. Have the assistant steer the boat through a safe channel while you make the carburetor adjustment.

Turn the mixture screw clockwise until the rpm on the tachometer gauge begins to fall. Stop. Turn the screw counterclockwise until the engine rpm begins to fall. Stop. Turn the screw clockwise until you reach the highest rpm number on the tachometer gauge. Perform the identical adjustment procedure on the second idle mixture screw next to it. Adjust the screw for highest rpm, according to the tachometer reading.

Locate the idle speed screw on the carburetor cam linkage. You will see an outside throttle cam on the carburetor linkage, and the idle speed screw will rest on it. Refer to your owner's manual for the manufacture's recommended idle speed for your engine. For example, it could be listed as 750 rpm for your engine.

Have your assistant place the shifter in neutral. Use a slot screwdriver to turn the idle speed screw clockwise to increase the engine speed. Turn the screw counterclockwise to reduce the speed. Set it according to your manufacture's specifications, while watching the rpm reading on the gauge. Stop the engine.

Replace the flame arrestor element if you have removed it. Place the engine plenum cover back on and screw the knob back into its seat. Unhook the tachometer leads. Start the engine and check it for smooth operation through several shifts.

Items you will need

  • Mercruiser owner's shop manual

  • Screwdrivers

  • Carburetor adjusting tool (flex-handle)

  • Tachometer

 How to Set the Idle for a 1992 Nissan Sentra

Park the vehicle and set the parking brake. Run the engine at normal operating temperature, race the engine to the between 2,000 and 3,000 rpm a few times under no load. Allow the vehicle to return to its standard idle.

Open and secure the car's hood. Mark the crankshaft pulley, located in the engine compartment, with a bright yellow paint pen. Start the engine and shine your infrared light from the tachometer on the yellow mark to record the idle rpm speed.

Disconnect the throttle valve switch at the throttle body assembly after turning off the vehicle's engine.

Re-start the engine. Check and record its idle speed. Idle speed should be within the specified rpm; GA16DE engine: 650 rpm for the automatic transmission; 800 rpm for the manual transmission; and for the SR20DE engine, 800 rpm for either automatic or manual transmissions. If the specified rpms are not within these parameters turn the idle adjusting screw at the throttle body until it is at 800 rpm, then race the engine to 2,000 to 3,000 RPM a few times under no load. Allow it to return to idle and re-check the idle speed adjustment. Once proper idle speed is reached, turn off the engine. Reconnect the throttle valve switch.

Items you will need

  • Screwdriver

  • Voltage-type tachometer

  • Bright yellow paint pen

 How to Set Idle on a 1989 5.0 Mustang

Open the hood and disconnect the battery. Remove the negative terminal cable from the battery first, and then remove the positive terminal cable. Leave both cables off of the battery for at least 30 minutes.

Locate the Idle Air Control (IAC) module on the throttle body and disconnect it. Reconnect the terminal cables to the battery and start the engine.

Locate the stop screw at the bottom of the throttle body and use a screwdriver to adjust the idle rpm. Turn off the engine and reconnect the IAC module.

Start the engine again, with all accessories including the radio, A/C and lights off. Allow the engine to run for two minutes. Turn the engine off and wait for two minutes.

Start the engine once more, this time with all accessories on. Allow the vehicle to idle for two minutes and turn the engine off.

Items you will need

  • Screwdriver