Hi Gary,

With all due respect, I think your "throttle body flap" is a mistaken conclusion. I base that on these words in your first post: "...plunger in air mass part is stuck...". There is no "plunger" in or near the throttle body, but there is one in the Fuel distributor & Airflow Meter, as I described below.

While throttle body service is probably worthwhile, I'm fairly sure it has no relationship to the problem you reported.

The early part of the K-Jet description below describes the "plunger" that I believe is stuck (as I have experienced).

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K-jet Cliff Notes

Just rambling here, hoping to pass on some info and maybe learn something if anyone spots a mistake. This is as brief as I can be, trying to outline the basics of, and interaction between, these K-jet elements:

• Fuel Distributor
• Air Flow Meter
• Control Plunger
• Air Flow Plate
• Control Pressure
• Control Pressure Regulator
• ECU
• Frequency Valve
• Oxygen Sensor

The Fuel Distributor (FD) is the heart of the K-jet system — the black lump with all the hoses, sitting on top of the Air Flow Meter (AFM). Inside the center of the FD is a Control Plunger that moves up and down. The higher the plunger moves, the more fuel is sent to the Injectors by the hydraulic action inside the FD.

What makes the Control Plunger move up? Answer: The upward movement of the Air Flow Plate below it in the AFM. As the engine turns and sucks in air, the air flow lifts the plate. The more air flow, the higher the plate lifts the plunger, and the more fuel the FD sends to the Injectors. The amount of fuel is proportional to the engine's need, based on the air flow plate's position, temperature, and O2 sensor input. If the plate doesn't rise, no fuel leaves the FD.

But there's another force acting on the Plunger: the "Control Pressure", which is a special fuel pressure derived from the basic System pressure inside the FD, and regulated by the Control Pressure Regulator (CPR). Bosch also calls this device the Warm Up Regulator (more on that later).The control pressure acts directly on the top of the plunger, opposing the air flow plate's upward movement — but only enought to damp out pulsations and keep the air flow plate stable.
The plunger's height relative to the airflow plate is adjustable (a 3mm set screw in the plate). This provides the FIRST of three types of mixture control in the K-jet/Lambda system.

The SECOND type of mixture control is the "Control" pressure itself. The amount of control pressure is controlled by the CPR. So by varying the control pressure, the the amount of plate/plunger lift can also be varied for a given air flow. For example, by lowering the control pressure on a winter morning, the plunger and air flow plate rise higher than they would otherwise (for a given airflow rate), and more fuel is injected. The amount of air to the engine, being controlled my the throttle, does not increase significantly. The result is a richer mixture for cold starts. Of course the Cold Start injector helps too, but only while cranking.

With the engine started, and in a "cold running" state, the CPR gradually raises the control pressure on the plunger over a period of 2 or 3 minutes by means of a bi-metallic switch-controlled heater (and by heat soak from the warming engine). This slow rise in control pressure gradually increases the downward pressure on the plunger, causing the rich "cold starting" mixture to lean out toward a "warm running" mixture. That's probably why Bosch calls the CPR a "Warm Up Regulator" (WUR).

Once the engine is warm enough, the Lambda ECU "fine tunes" the fuel mixture, by means of the Frequency Valve (FV) that operates directly on the Fuel Distributor to "tweak" the mixture.
At first a default (fixed) frequency is in effect. As the engine warms up, this changes to a dynamically variable frequency in response to the signal levels from the O2 or Lambda sensor (More below).

This Frequency Valve influence is the THIRD, and most precise method of mixture control. (Recall #1, the fixed airflow plate to plunger relationship, and #2, the Control Pressure pushing down on the top of the plunger, based on the temperature at the CPR/WUR.)

The FV is basically an electrically pulsed fuel injector, in a line connecting one part of the FD to another. The more fuel the FV letsflow thru that line, the more fuel comes from the injectors (not directly from the FV), thus richening the mixture for a given airflow. Less fuel passing thru the FV means a leaner mixture. This Frequency-based mixture control is separate from the temperature-based control pressure-control plunger influence mentioned above. A 50% "duty cycle" means the FV is open half of the the time, closed the other half. The higher the frequency, more the FVos open, and the richer the mixture.

While the engine is cold, the Lambda ECU pulses the FV at a fixed 60% rate to augment the rich mixture already provided by the lowered control pressure. When the engine temp gets above 59°, the ECU reduces the FV duty cycle to a fixed 50% until an O2 sensor signal is detected.

At that point, the ECU begins to rapidly tweak the FV duty cycle back and forth a few degrees, based on the Oxygen sensor (O2) signal. This signal should vary around a mid-point of 0.5v, ideally between 0.2v and 0.7v. Signals dropping below 0.5v (lean indication) cause the ECU to increase the FV duty cycle. Higher (rich) signals cause the FV duty cycle to be reduced. A Duty Cycle (or Dwell) meter at the red wire CO test socket in th engine compartments will show the frequency bouncing above and below the nominal 50% rate, and is easier to read (narrower range) than the digital voltmeter.

Summary:

• For cold starts, the CPR lowers the control pressure on the control plunger in the FD, which provides a rich starting mixture. (The Cold Start injector also helps while the starter is engaged.)The CPR heater and increasing engine heat cause the CPR to slowly raise the control pressure, to lean out the mixture for warm running.

• For cold running, the ECU also contributes to mixture richness by pulsing the FV at a fixed 60% duty cycle until the engine temp gets above 59°F. Then the fixed FV duty cycle drops to 50% until an O2 sensor signal is detected.

• For warm running, the ECU rapidly switches the FV duty cycle a few degrees either side of 50% as it tracks the O2 sensor signal level. The FV duty cycle can be read with as "Duty Cycle" on red wire test point in the engine compartment. It can also be read as degrees on a Dwell Meter, using the 4-cylinder scale where 50% of 90° equals 45°, the ideal mid-range duration.

Extra Credit: That 60° duty cycle for cool running richness may also invoked for acceleration on some cars, by sensing a drop in manifold pressure, or by a throttle micro switch.
(Fun-seekers can also control it with a toggle switch. But with these gas prices....?) 


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P.S. I haven't reviewed the above in some time, so there may be "imperfections";-)

--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.