High Idle speed on 1989 Merc Sable, 3.0L V-6. Approx 2000 RPM

.5 half way to 1 mark on ur rpm gauge

I think should be around 750.

All the above is normal , except 2000rpm is a little high at idle . can be adjusted down to 1500rpm. the computer adjusts the engine speed . in drive the transmission loads up the engine idle drops to 1000rpm . in park engine unloaded rpm increase all normal.

I will try to explain new electronic injection. There is an adjustment but you have another problem if the idle speed is too high.

When the RPM goes higher, it means you have an air leak, intake runner problem or higher fuel pressure than the stock setting. Or ISC (idle speed control solenoid) Think of it like opening the throttle slightly and letting more air into the motor or gas into the engine.

You can use a pump spray bottle of water with the engine running and mist the seams and vacuum lines and switches. A change in RPM indicates a leak.

Intake runner. These are like shutters inside the intake manifold. Modern intakes can have 2 levels of airflow separated by the intake runners. Sticking runners can let more air into the engine at the wrong time and affect idle.

ISC solenoid Is a valve that regulates airflow for the idle. Soot can cause it to stick in the wrong position. Removing and cleaning the port with WD40 can help.

High fuel pressure. If the fuel regulator sends more gas to the engine, the RPM will increase.

There is a set screw at the base of the airhorn to stop the throttle cable. It is called a throttle stop. There is a hex hole for an allen wrench and it has been coated with threadlock in some instances. Really it is not meant to be turned once the factory sets it. But you can do it. If anything fixes the defects I mentioned, the idle may be too low. I do not have the Specs or know if you have any optional engine. Generally the engines idle between 525-and 600 rpm.

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check all vacuum lines very closely for a vacuum leak. might be a small hairline crack that is hard to see.

A vacume line fell off or leaking.

P1506 - Idle Air Control (IAC) Overspeed Error This DTC is set when the PCM detects engine idle speed that is greater than the desired rpm.

• IAC circuit short to GND
• Damaged IAC valve

Disconnect IAC valve and look for little or no change in engine rpm as an indication of a stuck or damaged valve.

Yeah it sounds kinda high. There is no adj except for the idle screw on the throttle, the computer does the rest, if it has one. If not, then you can adjust it some how. If carbureted, check for 2 little screws in the front, and check the choke, If throttle body, then just the idle screw, the idle should be around 1000. Hope this helps.

there is a screw at the end of the throttle cable. get someone to rev the engine an your see it move.turn the screw anticlockwise and the idle should slow. clockwise will raise the idle speed.

Check your vacuum hoses (They are 3/8" Rubber hosing on the right side of the engine, you will need to remove the air intake piping (Also remove the throttle body to make accessing them easier) This is the #1 cause of high idling in the 3.0 OHV and 3.0 DOHC sable engines.