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The throttle bodies are adjusted for a certain flow at the factory and secured with a drop of paint. They are a never touch item, following the manual.
To get it right again when the butterfly stop has been disturbed or other cams are fitted(!), there is a procedure that was released as a service fix for other cars with the same injection system and components.
Be sure there are no leaks behind the butterfly. Check all connectors and hoses for cracks and fallen of parts. It is a good idea to renew them as they are very aged now and all have gotten very brittle, sometimes only at one end. Often they only stick to there position, letting false air in.
Basically with the engine at working temperature (cooling fan has started for 2 times) you disable the idle solenoid (or IAC valve =idle air control valve) electric connector and completely turn in the idle adjustment screw. Disconnect the O2 sensor signal cable.
Then you open the throttle stop until the car has a basic, low idle at about 650 rpm, but does not stall. The butterfly must be lifting a tiny in any case, to prevent it from sticking and wearing. If you need not to open it at all, there is a false air problem to fix!
If done, secure the throttle stop with paint.
Then adjust the idle to 750-800 rpm with the idle screw. It should react very spontaneous.
Last, connect the electrical connector to the IAC. The idle should be rising a few rpm (about 50) and be very stable at 850. Reconnect the O2 sensor.
It can be unnecessary to disconnect the O2 sensor for the procedure, if no stable idle can be achieved this way.
A bit of oscillation of idle rpm can not be avoided with most engines, because the O2 sensor makes for a permanent change from rich to lean, which is right if anything is OK.
If there is still no satisfying idle, independent of engine temperature, the CO may need some adjusting too. If you follow the manual, you have to use a CO tester connected in front of the catalytic converter and set it to about 1.0-2.5 % CO without Sensor connected to the ECU. But usually this setting is OK. All together a job for experienced mechanics that have a feeling for engines.
There may be other procedures for this task, but they all have the same aim: Get the adjusting devices, to operate at their best basic setting. Because the O2 sensor and IAC are disconnected, there is no active correction and you are automatically going for the best setting if you follow the instruction. Only if this setting is right, the IAC can perfectly control the idle , because it follows a map and works the better the least correction it has to make to the preset duty cycle. A basic workload has to be seen, that is why the idle set by the idle screw has to be a bit lower than the programed target rpm in the ECU. It can be neccesary to find the IACīs sweet spot with the help of the idle screw. But IAC connected and not connected have to make a difference in idle RPM.
The numbers given may vary a bit, depending on the instrument that measures RPM. If your cars manual shows other values, use them.
All basics like valve lash, cam timing, ignition parts, air filter, compression, etc. have to be in good working order prior to doing this adjustment, please!
With performance cams there may be no idle at all until you adjust the throttle stop, as these can affect the AFM because of strong pulsations!
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