What would be a highly probable cause for the engine to be idling at about 950 rpm, in park? In drive its about 800 or more. The book I have says there is no base idle adjustment and computer takes care of that. If there is no base idle adjustment then why would there be an adjustment screw and lock nut by the carburetor throttle? This screw is backed off the throttle lever and the idle is still running high. Could it be timing, of which I cannot rotate the will not turn distributor? I have tried checking hoses and cannot find any leaks. Any ideas, anyone?

Thanks you

 

800 RPM is acceptable speed in D, why do you want it to be less?

 

your throttle body may be a bit gummed up so its not closing all the way, so you're never really getting to the regulated idle mode.

 

Robert Bently 240 manual states 775 +/- 20 rpm which I assume to be in neutral. 900 rpm with A/C on.

 

Well, I don't know about Bentley but many RPMs are to be measured when in D, parking brake ON. Even at 900 I wouldn't worry about it...

Are you using the car's tach or a separate gauge? That in itself may be OFF, easy to misread a +/-100RPM. Then you are talking about a 20 yr old car: perfection is not easily reached.

If you must, you can manipulate the screw at the throttle but I don't see why you'd even want to try unless you were getting a big CLUNK shifting between the gears...

 

The idle circuit on these is pretty straightforward. It is a simple feedback mechanism controlled by the ECU and should give you an idle speed around 700 RPM regardless of in gear or not (when the air is on though, the ECU compensates to give a higher RPM).

When the throttle body is completely closed, the throttle position switch should turn on engaging the idle air controller. Basically, the idle air controller controls the amount of air entering the intake. The ECU signals the idle air controller to let the right amount of air in to keep the RPMs at 700. The idle air controller sits under the intake manifold and has an approximately 1 in tube that connects to the accordian air intake tube and another 1 in tube that runs to the top of the intake manifold.

As Pierce said in his post, many times the throttle body on these engines get gummed up resulting in the throttle not closing completely. This keeps the idle circuit from engaging causing all kinds of idle issues. With the key in the II position and the engine not running, turn open the throttle a bit and then release. When released, you should hear a click in the throttle position switch (the black think on the rear of the throttle body that has some wires connected). If you hear the click, then the sensor is operating properly.

Also check the inside of the throttle body. Is the butterfly valve closed all the way when the throttle is released? If not and the throttle body is clean, then you can back off the adjusting screw until the butterfly valve closes completely.

Hope this is helpful