Mechanics

ERRATIC IDLE SPEED

1996 Mercury Sable

Engine Performance problem
1996 Mercury Sable 6 cyl Two Wheel Drive Automatic 75000 miles

My 1996 Sable frequently idles at 900+ RPM in Drive, jumps to 2000 in Neutral. This happens on a cold start, or frequently after 1/2 hour of driving following a warm start. Frequently, turning the engine off and immediately re-starting it will fix the problem temporarily.
I have replaced the Idle Air Bypass valve, and cleaned the Mass Air Sensor. I have had the car back to the dealer's twice, but it always behaves fine at the dealer's. When I get the car back it runs perfectly for about two weeks and then starts to act up again. The mechanic says he has done nothing except to connect the computer and run the car at idle for a while. Apart from charging $98 for not diagnosing the problem, the dealer has done nothing to help me.
Any help would be welcome.
Would it make sense to buy a cheap engine code scanner and leave it connected while I drive?

Thanks,
Walt
Avatar
Walts
October 20, 2008.



Recheck the idle air control valve and test the TPS

Here's how to clean the IAC valve:

Disconnect the air intake ductwork from the throttle body.

Start the engine, then increase and hold the idle speed to 1,000 to 1,500 rpm.

Spray the throttle cleaner or engine cleaner into the throat of the throttle body, aiming for the idle air bypass port (usually located on the side or top of the throttle body opening). Give this area a good dose of cleaner (about 10 second's worth).

Turn the engine off to allow the cleaner to soak into the IAC passageway.

Wait about three minutes.

Restart the engine, rev and hold at 1,000 to 1,500 rpm, and repeat the cleaning process again.

Turn the engine off again, and reattach the air intake ductwork to the throttle body.

Start the engine and rev and hold to 1,500 to 2,000 rpm until no white smoke is coming out of the exhaust pipe.

If this fails to make any difference, you can remove the IAC valve from the throttle body and spray cleaner directly on the tip of the valve and/or into the ports in the throttle body. Let the cleaner soak awhile, repeat as needed, then reinstall the IAC valve, start the engine and run it at 1,500 to 2,000 rpm as before until no white smoke is seen in the exahust.

If the idle speed still surges after this, the IAC valve is defective and needs to be replaced.


http://www.2carpros.com/forum/automotive_pictures/12900_iac_valve_ford_3.jpg


Rasmataz
Oct 20, 2008.
You said to clean the IAC valve, and I will do it, although the valve is new about 3000 miles ago.

You also said to test the TPS - how do I do that?

You didn't answer my question about an engine code scanner.

Thanks,
Walt

Tiny
Walts
Oct 20, 2008.
Do you have a check engine light?

You didn't answer my question about an engine code scanner. The only thing a scanner does-it gives the OBD2 codes-Now to view live data you need a scantool. You can go to Autozone and get read free-

The TPS ( Throttle Position Sensor ) measure its voltages-see below


http://www.2carpros.com/forum/automotive_pictures/12900_tps1_6.jpg


Rasmataz
Oct 20, 2008.