Huh... The plate is moving - I am not exactly sure how the idle control valve modulates the air in the intake (some one else can help) BUT I would think that it would not involve changing the plate's position, more likely to bypass the whole throttle assembly.

I thought the plate would only move via the throttle body or equivalently the throttle cable OR perhaps cruise control (could there be a problem here?).

Saumil

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Saumil S. Patel

If the throttle plate is sitting too high, it simply could be struggling to get enough air so the ICV keeps opening+closing to stabilize the idle. When it is unplugged the system is in open loop so the throttle is pushed open further. Or at least as far as I understand. So I would make sure that the throttle plate is both centered, and the HEIGHT is correct. The height is adjusted via the two small "pins" to the right of the fuel distributor. They are 2 circle button-looking items. Unless you are sure though leave them alone as the only way to push the plate back "up" is to remove the assembly and push the pin from the inside.

Here is the FSM PDF on plate adjustment:


If you don't have a feeler gauge, I just used a piece of paper as it is roughly .5mm

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Saumil, ps2cho, thank you for your input.

I may be missing a point here but I think Idle Air Control Valve takes air in after the sensor plate but before the throttle, then to intake plenum (after throttle plate), so its opening should have the same effect as throttle opening, and to allow for more fuel for higher rpm via metering plate opening.

What puzzles me is that engine idles absolutely perfectly when Idle Air Control Valve is unplugged. And when plugged in, RPM oscillates rapidly. So, metering plate mis-adjustment is somewhat unlikely. I actually pushed in metering plate a bit at one point and doing so did not stop RPM oscillation as Idle Air Control Valve kept opening/closing. I will double check this this weekend though. Maybe I need to push metering plate harder.

I owned a number of cars with K and L Jetros in the past (not KE though) and this issue was always due to sticking Idle Air Control Valve. Just cleaning it with a heavy dose of carb. cleaner fixed it - of course those valves were simple opening plate with bimetal strip and heating coil attached to it - not a servo motor like this KE system's). This time, I have a brand new valve that actually is doing exactly what CPU is commanding. So, I keep thinking that either CPU is getting a wrong info (frail wire, corroded connection, fried unit, etc.) or proper signal is not reaching the valve (frail wire, short, etc.).

What do you think?

By the way, when motor does not do this oscillation, it runs oh so sweet. Smooth, perfect idle to nice even delivery of power to higher rpm. It is quite quiet, not a miss of any sort. Just perfect...

Then, out of blue, it may start oscillating.

Well, my car did not misbehave even for a second all this weekend. It ran perfectly, so I could not test anything. O2 warning light came up fine, went to fast idle, came down to 800-ish rpm range and pretty much stayed there for 2 days (except for occasional trips to 1,000 rpm right after I disengaged gear into P or N).

I wonder if my problem had anything with a bad gas as car still had some of 2-year old gas in it (mixed with fresh gas). I also plan to replace fuel filter next change I get.

I plan to tackle this problem again as soon as it comes back. Since I am in Chicago area, it is getting close to a winter storage time. If I cannot report back to you guys for a while, I apologize in advance. I will close this thread one way or another - though it may take little longer than I planned. Meanwhile, thank you all.

hey i could not help but try to help coz for the past 6 months i have been having the same problem with my MB w124 260e 1987, it can be a real bore coz it goes n comes back and i mine the same way like yours mine has also been asleep for almost 2 years. i think you should change your 02 sensor to a new one and your problem will go away. if you have checked the idel sensor and it seems to be ok then am sure it is the 02 sensor sending a bad reading when i changed mine the problem went away.

Thank you for your input. As I did not have O2 sensor warning light on, I never suspected it. During a warm-up, does this system run open loop?

In any event, it's worth a try.

Interestingly, it has been running like a champ since I filled it with premium and 2 ounces of Sta-Bil Marine formula a week ago. Car sat for a long time and I wonder it had a bad gas in the tank.