MIke pull the potentiometer and look at the slides let see if they are worn. Mark it and take out the 4 torq screws. then we can see if it is indeed worn out.

m

It seems unlikely to me the pot would be the culprit if everything functions perfectly, then starts screwing up. Particularly if not accompanied by a hunting idle. If you unplug the pot and the symptoms persist, then look elsewhere.

Steve

This is a tough one, I would expect a fluctuating idle or high idle when duty cycle is 10% (engine idling @ normal operating temp)

Sbourg has a point.
BUT why then the diagnostics port would give a 10% fixed duty cycle? (potentiometer malfunction)

Ok, did some testing today:

This morning: Started her up- everything working normal.
KOEO: EHA 20mA
DC 69.9%

Idle: Fluctuation around 50%, but on occasion going down to 30 or up to ~65. Idles at correct speeds and is pretty steady- no real hunting.

Decided to try driving with EHA unplugged- no good. Car has no power, and struggles to accelerate. Fuel Econ guage usually in the red.

Plug EHA back in. Drive car around and stop my local MB shop (indy). He says airflow meter may be getting stuck once car is hot, and these can stick in either lean or rich posistions. Tell him ill keep this in mind on my search.

Start to head home and while the car gets up to speed fine if I take it easy, If i try and accelerate from 50-80, she struggles if given any gas. If i put her in third, the car just sort of bucks and the engine struggles to "catch."

Put'er in the garage and pop the hood while she is still running.

DC 10%, mostly stuck on this number.
EHA 2.05

Let idle for 5 minutes and turn motor off, leaving car KOEO.
Reading at pin 3 is 9.9%. Checked it twice to make sure.

``````````````````````````````````````````````
Let the car sit for ~2 hours. Check things again:
KOEO- 69.9%
EHA 0.0

Starting car now is difficult. Will not hold idle without giving it some gas for about 30 seconds. Runs a little rough.
<<Second time this has occured. If I wait until morning, it starts instantly with perfect cold idle>>

I check numbers while its idling:
10%, 0.0 for the EHA.

Diagnosis: Car possessed:eek: :confused:

Won't be able to mess with it anymore until tomorrow night. Martin, I will check out the potent.meter.

Sbourg-When you say "unplug the pot," do you mean the EHA connection?

Thanks everyone. Mike.

No, the pot is on the airflow meter body, as in the pic. The EHA is on the other side of the fuel distributor.

Steve

Ahh. Of course. Had my terms mixed up. Pot= Potentiometer. Got it.

haven't had time to pop the hood these last few days. Hopefully this weekend.

Thanks, Mike

WHAT DOES MEAN DUTY CYCLE 90%
 

Excuse me Sirs. This interesting threadid sounds like relative to

my problem.

In my 190 E, 2.6L, 1988, I have instaled and calibrated the new

POT, new O2 sensor, new OVP, New Breathing hose for ICV, new

Injectors, new plugs, new hex key repair kit, new vaccum hose,

cleaned the air flow meter and plate, cleaned de IDLE C. Valve,

new EHA, new throtle switch, however I get 90% when contact

the DMVM positive lead to the Pin 3 and Black to Pin 2.

But only contact the positive lead to PIN 3, without contact to

ground the DMVM Black lead, I get only Duty Cycle 36% to 42%

but never 50% adjusting the hex key 3mm.


Please, what is wrong?. Also the RPM is 800 at 80ºC at the

begining and fall till 400 one hour later.


Thanks.

Mario Farias
laprefar@cantv.net

Where would I find those pictures, please?

Thanks

Where would I find those pictures, please?

Thanks

Well, this is amazing. My '91 300E is displaying the EXACT same numbers. It's had an intermittent problem for years but now has failed entirely.

One thing that used to work for me...after the engine was running a few minutes I would push the gas pedal to the floor for just an instant and all would work normally after that. The pedal had to go ALL THE WAY to the floor or it had no effect. The car would run normally after that until the next day, when I had to do it again. This maneuver worked for over two years but quit working about a week ago.

My numbers are:

koeo Cold: DC 69.9 EHA 0

Running warm DC 9.9 and EHA exactly 2.0ma - stuck there but EHA will actually enrich to about 5ma when it should do decel shutoff and it will enrich a bit at WOT.

koeo Warm DC 9.9 and EHA 2.0

After it cools off it goes back to normal...69.9 and 0 koeo.

Mostly I can tell if things are working right by watching for decel shutoff on the tach. When I don't see it I know I again have 9.9/2. I do get "proper" numbers briefly from time to time...but very rarely.

Hurry up and fix yours and tell me what it was! Try the "floor-it" maneuver and see if it has any effect.

Michael Brewer :confused:

Well, this is amazing. My '91 300E is displaying the EXACT same numbers. It's had an intermittent problem for years but now has failed entirely.

One thing that used to work for me...after the engine was running a few minutes I would push the gas pedal to the floor for just an instant and all would work normally after that. The pedal had to go ALL THE WAY to the floor or it had no effect. The car would run normally after that until the next day, when I had to do it again. This maneuver worked for over two years but quit working about a week ago.

My numbers are:

koeo Cold: DC 69.9 EHA 0

Running warm DC 9.9 and EHA exactly 2.0ma - stuck there but EHA will actually enrich to about 5ma when it should do decel shutoff and it will enrich a bit at WOT.

koeo Warm DC 9.9 and EHA 2.0

After it cools off it goes back to normal...69.9 and 0 koeo.

Mostly I can tell if things are working right by watching for decel shutoff on the tach. When I don't see it I know I again have 9.9/2. I do get "proper" numbers briefly from time to time...but very rarely.

Hurry up and fix yours and tell me what it was! Try the "floor-it" maneuver and see if it has any effect.

Michael Brewer :confused:

Brew- Looks like we are in this together!

I'm sure you have read through the thread entitled "duty cycle sticks at 10%." Some good info there.

I will finally have some time the next few days to get serious about fixing this problem. I plan to follow the advice given here and pull the potentiometer. I will post pictues here as soon as I do and maybe we can continue to compare notes. By the way- what type of cold starting symptons so you have, if any?

I will try your "floor it" method and see if I get similar results.

Can one unplug the potentiometer and still run the car? What should happen if it is unplugged?

When the potentiometer is taken off the AFM, what type of precautions must be taken as far as marking positions and so on?

merry christmas guys!

Mike

The pot can turn ever so slightly and mess up the alignment. Beast thing to do s to use an exacto knife and mark the top edge. So just outline the top of it into the air flow meter. Make sure you to that before loosening those t-15 torx that hold the pot on.
Merry Christmas
David

Thanks for the reply David. I will try and document with photos.

Mike