Yes, you are right. This graph has the lower duty cycle on the side that states rich. I think it is a mistake from its creator (whether the graph is right or wrong I am not to be credited, I just borrowed from one of the forum's member's website). According to the manual a low duty cycle means a rich mixture. The article from Stevebfl in the DIY section "Evaluating Electronic Engine Controls" mentions a duty cycle of 35% as rich.
Quote: "The value of 38% indicates a rich reading".
The fact that your duty cycle drops when turning CCW is waaaaay over my head.
Experts, please take me out of my ignorance, explain this matter.

__________________
1999 Porsche 996 Carrera Convertible
1994 420E - SOLD
1986 300E - SOLD, what a car
609 Certified

Pesuazo,

If you have a volt meter that reads duty cycle, we could settle this discussion. Maybe Pat or Dave could chime in here. Guys where is your duty cycle set? Would you mind terribly leaning it slightly to see which way the duty cycle readings go? You gents might discover why your cars are running so poorly. A fixed reading indicates a problem. Have you guys pulled the resistor (R16?) out of the wire harness to advance the timing???? It makes does make a slight difference on these 16V motors.

BTW wifes 87 16V auto usaully runs right around 20mpg. With a 5 speed I would expect a bit more.

Tinker

Thats why I am so confused, I do own a meter with duty cycle. I have the CD manual with the codes and all the diagnostic testing. I have become somewhat profficient at diagnosing my lambda control.
When I go CCW, I see my duty cycle go up, CW it goes down, just like the manual states.
For what I understand the Duty Cycle (in an ideal system) should oscillate between 45-55%, at idle and at 2500 RPM.
There is an acceptable 10% difference. ie. 40-50% idle and 50-60% 2000 RPM is OK
Mine normally oscillates at 41-48% idle and 49-57% at 2500 RPM. And those values were achieved "tinkering", just like your name.
Obviously all the inputs are OK, since I have no fixed duty cycles.
Except when cold, I get 50%, when it warms up it oscillates (which only makes sense, since closed loop happens only in a warm engine)

__________________
1999 Porsche 996 Carrera Convertible
1994 420E - SOLD
1986 300E - SOLD, what a car
609 Certified

Pesuazo,

I don`t doubt you. I wish the other 16V owners would chime in.
Although it would be a bit strange, perhaps the 16V`s CIS program was designed differently??? I doubt it. Bad computer?

Scratching my head.

Tinker

Calibrating the air flow meter is not that hard at all, it just seems this way

all you need is a good multimeter and LOTS of patience.

Mine was glued on and I decided to rip it off and put it back the way it should be, why it was done this way I dont' know but it's fixed now

What I did is set it to it's lowest possible reading, this takes micrometer precision so make sure you got a steady hand.

also don't let it be too lose when you are adjusting it because the slightest movement will set it to some catastrophic value.

that's all there is to it really, worked for me at least.

stupid guy told me I would need the entire air flow meter asembly which is $800 or more

took me an hour to fix the problem.

xp

Hi xp:

Did you purchase a new pot or just cleaned the old one?

Did you take pictures by any chance?

I read somewhere (stevebfl?) that a pencil eraser can be used to clean "something" inside. I am dying of curiosity. I don't want to open mine up for fear of getting stranded. I only have one car, this one, and the word catastrophic does not help either.
I certainly don't have micrometer accuracy with my hands.
I searched and searched the net, but could not find a seller of the pot by itself.

__________________
1999 Porsche 996 Carrera Convertible
1994 420E - SOLD
1986 300E - SOLD, what a car
609 Certified

I have been struggling with my cars drivability for the last 8 months after replacing my car's potentiometer to fix a stumble on acceleration. The stumble ended up being a defective distributer cap so I reinstalled the original pot after cleaning it with alcohol.

When reinstalling it the only procedure check that I have was to get the unit to increase continuously to approx 5 volts when the sensor plate is deflected, per my MB manual. Is this critical? If so why does my CD rom manual so vague?

Since this time I have been unable to get the car to idle reliably. Sometimes it idles fairly good with just a slight dither between 950-1100. Other times it will stall repeatidly at idle. Still other times it hangs at 2000-3000rpm. I am very suspect of the CIS control unit being bad from my tinkering, but based on some of the other posts I am not alone in my problems. So maybe the Control Unit is OK, just the system is out of adjustment.

I took the car into a shop to fix and they simply drilled out the mixture adjustment plug and tampered with that and then concluded that they could not fix it either. Now I have no idea what is right anymore.

I do have the MB manual and have checked a number of the devices and have found everything to be within spec in terms of resistance values and the EHA when checked seemed to be at the proper duty cycle at idle.

The car is currently running rich based on fuel mileage 17mpg and black soot coming from the tailpipe. but when I adjust the mixture screw the idle has a tendancy to oscilate violently and stall repeatidly.

Currently I have my multimeter hooked up to the O2 sensor and am curious about the signal from that. Once the car warms up the signal is around .8-.9 volts most of the time, but then occasionally it will oscilate from .1 to .9 as I think it should but then a few minutes later it again hangs at .8 or .9.

Any suggestions would be appreciated.

Zeilekd,

What kind of car? 16V? You checked the duty cycle at the X11 plug? And what was the duty cycle? What is the ma at the EHA? That will give you an idea if your mixture is close and if the O2 is functioning.

Tinker

Tinker,

86 2.3-16 190e

Since the shop adjusted my mixture and my potentiometer is out of adjustment I have to ask which one to adjust first and what the procedures are. Is it wrong to assume that the O2 sensor either works or it does not? My biggest frustration with the car is that nothing seems consistent. I do not understand how a Potentiometer or Mixture being out of calibration would cause different operational problems when all other operational conditions (outside temp, engine warm up time etc.) are the same. This is why I question the CIS control unit. Something is arbitrarily causing the ECU to send bogus signals to the rotory idle air valve. Can this be the potentiometer? Also what about my O2 sensor hanging at .9 volts then a minute later adopting the oscilating voltage with an average at .5?

Kurt,

I don`t think the shop you took your car to was very knowledgeable. Did you mention to them that you reset/cleaned the potentiometer or did they come to the conclusion that the air meter was out of adjustment on their own? I know some other posts indicate you can set these by yourself. From what I have read, the concensus seems to be that you can not.

Also, from what I have read/been told, the CIS computers almost NEVER go bad.

The voltage from your O2 sensor should fluctuate. They can get fouled or burned out. If you are seeing mv in the 0.1 to 1.0 range from the O2 WITH the heater wire hooked up, it more than likely is alright. If it is stuck at 1.0 mv, I believe that is a rich condition. Where did the shop set your mixture? Did they say it was lean or rich? If the air flow meter/piotentiometer is messed up, the voltage signal it sends to the ECU will be off causing the computer to make attempts to correct. Have you monitored the voltage coming out of the air flow meter?? You can disassemble the connector on the #4 runner so you can monitor the voltage while your driving. I did this for a weekend and could not find any spikes or open curcuits in mine.

Do you own a volt meter with a duty cycle function? As Stevebfl writes about, you can check the system by monitoring the EHA amperage and the duty cycle readings. You will get a much better idea as to what is going on. If you get fixed duty cycle, the number provides you a hint where the problem lies.

Let us know.

Tinker

today I took of the air mass potentiometer and the part number
is 3-430-591-017 , this part is wasted worn down to silver metal
I can not find this number any where on the web to buy a new one
the numbers you guy's gave me is 3-437-224-035
is this the new number?? I can find this one everywhere
any thoughts on this??
thanks
Dave

Dave, if your part# is different, the part may not be the same. However, if it looks identical to the ones I pictured, then chances are good it is the same. The resistance measured between the outside circuit board solder tabs is about 4000 Ohms. The 'low' end of the board has a trimpot wired in series from the solder tab to the connector pin. The other two solder tabs connect directly to the other two pins.

Steve

This is such a classic problem to all of us the 16V owners. Since the calibration procedure to this air mass sensor assembly is so intend and not so sucessfull.
I have the same problem with my car too and nothing seems to have fixed, so one day I adjusted the hex key about an eight of a revolution clockwise and the car seems to love it. It becomes very responsive thru out the whole RPM spectrum and no more getting stuck at high idle.
I have to admit that this is all luck.

Alex

I think, though, that a mixture adjustment cannot substitute well for a worn-out pot. Since that adjustment is a calibration for the mechanical action of the airflow meter on the fuel distributor, it should need to be made if the airflow meter body (i.e. the MB part) is replaced, or it there has been enough mechanical wear. The procedures described on this site involve measuring the EHA current to determine how much it is compensating for an incorrect mixture.

I was surprised by how easy replacing the worn pot was. I was careful, and pre-adjusted the new one to be as close as identical as my DVM could resolve. That done, it was plug-and-play. No mixture adjustment should be needed.

I don't know why the bad pot was causing the idle speed fluctuation and decel surging, but I have a theory:

[WAG] At steady throttle, and demand of the engine is essentially constant, the pot sensor return to the ECU is a fluctuating voltage where the wiper hits the worn spot. The ECU interprets this as 'leadfoot' and tells the EHA to go rich. Since this wasn't actual demand, the Lambda sensor tells the ECU 'very rich', and since we are signalling 'throttle closed' too, it compensates by opening the idle control valve more. [end WAG]

I stress - I really have no source that tells me this is what happens, but it seems reasonable for the symptoms.

Steve

ya I'm only getting 1400 ohm on the outside pins, plus it 's much more worn out than yours in the pictures, but it is exactly the same .(not the #'s though).

Ordered a 3-437-224-035 from Phil with new injectors,seals housings, see if this does the fix?, If not new governer then?