'93 300e idle surging - fault code 009...advice needed
 

hello,

i just purchased a 1993 300e with 67,000 miles. an excellent driver but has a surge at idle ranging from 500-1100 rpm. i scanned the ecu and am getting a 009 hfm signal too high code.
my pockets are not deep enough to throw parts at it so am i looking for advice to further diagnose the issue. any comments appreciated!

thanks in advance,
rob

I believe that would indicate a faulty Air Mass Meter (hot film meter). You can find used ones for around 100 bucks. Dont quote me on this, it could be wiring going to it, or maybe something entirely different.

Good luck.

I show code 9 as being -- intake air temp sensor-open or short circuit-- not sure if this is the same as what amg280 describes or not. Check the sensor to make sure it is plugged in securely.

http://www.batauto.com/MB/

Good luck!

I have a 1993 300E and had a surging idle similar to what you are describing.

Common causes of this sympton usually are:

1. mass air flow meter
2. vacuum leak
3. throttle actuator

My problem in the end turned out to be a vacuum leak at the intake manifold. My crack mechanic figured this out after changing a $961 actuator and a $250 mass air meter.

One more thing - does your cruise control work?

Another symptom of a bad throttle actuator is a mal-functioning cruise control.

Our wonderful German engineers designed 3 or 4 separate functions into the actuator. If any of these go out, you're replacing a $1,000 part.

For reference in the future I would suggest, on a good running car, to disconnect a vacuum line at idle and watch how the car runs/idles. Try disconnecting a small one and a large one. Disconnecting a large one will make the engine run REAL rough whereas the small ones are not quite as bad but do show up. Also, if you want to get real adventursome disconnect the MAS meter and watch the idle.

I recently resolved a very, very slight "miss" at idle on my E320 and found that I had the plugs gapped too close together.

Do as Paul said..
The Intake Air Sensor is located on the driver side of the intake cross pipe.
They usually forget to plug them back in when sevicing the car..
If it is plugged in, then unplug it and test it w/ohm meter.

Hi Rob,

I get heated O2 sensor open circuit for code 9 HFM-SFI. The DM gives Air temp sensor for its code 9. The airtemp sensor won't cause the surging. The O2 sensor probably won't either although the code could be an indication of a vacuum leak or AMM problem (if the code 9 was on the HFM).

I'm thinkin that I drove your car yesterday and taking off I was in some rain water and your traction control took over. This would indicate that you have EA/CC/ISC instead of just CC/ISC. It would be interesting to see the codes on that module also. This would be on pin 14 of the test connector.

SB is on the right track..
I was assuming [that never works] a code 9 on DM. BUT,
You have a HHT 009 code on the HFM module, which is , as you already know, MAF sensor problem..
Might want to check the boot clamp at the intake before anything

This would also be a flash code 4 on pin 8 [HFM mod.}

Am I with you now?

thanks to all for the responses to my problem. i initially scanned the other sockets with the following results:

7) code 13-ect open circuit
8) code 009 amm signal too high
14) codes 112-can:fault in transmission from efp n4/1
182-safety fuel shut-off switch signal n3/1
224-idle speed contact switch s29/3

i have also since discovered that i have the dreaded wiring harness insulation flaking syndrome. the good news is that my local dealer agreed to do it for 2.5 hours labor and no parts cost. i hope this cures my ills but with the number of faults stored, this may not be the case. i will report back after the harness replacement later in the week. btw, thanks stevebfl for your assistance and the alignment gave the vehicle a better "feel".

best regards,
rob

follow-up report

hello all,

i had the harness replaced two days ago having to pay only labor as the dealer goodwilled the part. the engine still exhibited the intermittent rough idle, surge, and hesitation. also, i rechecked the system for faults and the 009 hfm was still present. i replaced the amm today and am amazed at the performance i was missing! having only had the car for two weeks and it being my first w124, i think i'll keep this one for awhile. thanks again to all that replied.

best regards,
rob:D

Please don't judge me harshly if i did not comepletely understand the wiring harness part.
I have a problem with fluctuating idle on 124032( e320 hfm-sfi)
Idle speed rises from 500 to 1100 intermittently in P/N. The interesting part is that no faults are detected, but disconecting the airflow meter seems to make the problem go away. I replaced the airflow meter from a car with no such problems, but after a while idle is surging again. Wiring harness?
I also monitored the signal coming out of amm: if the signal wire(disconnected) voltage is measured against ground while the other wires are connected- signal is beatyful. If the signal wire is connected- my Bosch PMS shows voltage surges when the fluctuation stars.
Or should i look for vacuum leaks, dirty isc, faulty output from transmission?
Thanks ahead - est

Disconnecting the airflow sensor will of course put you in open-loop 'limp' mode, which will probably be a pretty steady idle. Mixture will be off, but if properly adjusted, probably not a lot - but enough to fail emissions.

Anyway, I would first look for air leaks in the idle circuit, anything that will prevent the airflow meter from properly gauging that parameter.

Steve

Thanks.
I am very well aware that the leaks can cause this problem, and my first guess was that the tank ventilation valve is stuck, but replacing it did not do it. Also, one by one, i took every vacuum hose off the manifold and plugged them up- did not help either.
ISC was taken apart and checked- everything looked very well. This car does not have the 14th pin in the diagnostic socket
The idle got even worse over a week. Now the fluctuations are in every mode - driving in traffic, reversing, parking. Also the CU gives me the " airflow mass sensor signal- voltage too high" constantly. I checked for the short circuits in wiring and found none. New air flow meter is ordered so i will have to wait and see what happens. Any comments and advice are very, very welcomed.

I will be watching your thread closely, as I am dealing with the EXACT same issue on my W124.

Idle surge for the last two years, and has gotten worse. Also sometimes stalling out when starting cold and putting in gear.

Balking on ordering the part just yet, so I will see what results you achieve...

Finally the amm arrived and after installing everything started working like it suppose to. Conclusion: hfm air mass meter does not break- it wears out and with time, the measurment of this device becomes inaccurate wich leads to richer mixture, which in case leads to the clog up of Lambda sensor and catalytic converter.
The new Lambda sensor (which was installed before the aam) caused even greater fluctuation of idle speed, trying to correct the mixture.
This is my humble opinion, so please correct me if i am wrong, because i really wanna understand how the newer injection systems think.

Onthe OBDII cars, the MAS is set to trigger a CE light pretty quick, as running with a defective MAS not only causes driveability problems, but it can break other emissions bits.

Think the MB MAS is $$? Our Mazda 626 needed one, and the Mazda OEM part was $1300. We got a used one for free...

Amen to that! The price is definately not liked by customers. The thing is that european cars do not have the mil light. This amm fault can cause malfunction of lambda sensor and catalytic converter.

I am having the same surging problem on my 1993 300e with a 3.2 engine.

So far we (the mechanics that is) have replace the O2 sensor after getting a flat line reading intermittantly. No help. They cleaned the idle control valve out which was mentioned in another thread, no help.

My symptoms are, slightly rough idle when cold, about 20 minutes into my commute the idle starts to surge and the exhaust stinks like the cat is bad. A friend said that might be the car leaning out and the cat "cooking"

There are no apparent vac leaks, and the harness recall was done on the car in the past.

The mechanics had a 1994 320E at the shop that runs fine, so they swapped in the known good Mass Air meter, and there was still an intermittant surge when warmed up.

No check engine light.....

Need more suggestions?

Your engine does not have an idle control valve. M103 and M102 engines have idle control valves.

M104 engines have a throttle actuator, which electronically controls three functions: Idle speed control, electronic accelerator, and cruise control. I don't believe it can be cleaned to fix the problem.

I don't know if the problem is your throttle actuator or not, but if replacing the Mass Air Meter didn't fix the problem, and if you don't have a vacum leak, then I would point the blame at the throttle actuator.

They usually fail for two reasons:

1. they have potentiometers that wear out over time.
2. they have a wire harness that has bad insualtion which flakes off, which cause the actuator itself to malfunction.

I understand that one test for this throttle actuator is to try the cruise control. I will check it today and post results.

Would the Throttle Actuator on a 1994 E320 be the same?

If so my shop has one that they possibly swap the part onto my car for testing. Is this thing a b!+ch to R&R?

Thanks for all your help, I think I need to find someone a little more competent with MB. I am using my BMW mechanic for my Benz and he just doesn't have the technical savvy.

Did you keep the old, now known good actuator? If it turns out to be the part I need I will buy your old one.

I ended up installing the new actuator because I couldn't return it, and selling the old one.

Yes, 1993 300E (3.2)'s and 1994-1997 E320's use the same actuator.

In fact I think S320's until 1999 used the same actuator as they have the same engine.

The cruise control works, so would that totally rule out the actuator as the problem?

I am currently looking for a Benz shop to diagnose this problem in the Nassau/Suffolk border area of Long Island. Any Suggestions?

Well, your cruise control can still work fine, and the actuator could still be bad.

The point is that if any of the three functions the actuator controls fails, then you have to replace the whole part.

I agree with you in that you need a mechanic who specializes in Mercedes to diagnose the car, whether at a dealer or an independent.

Two Mercedes independent shops that tried to fix my car couldn't find the vacum leak. They suspected it, but determined that there wasn't one.

The dealer took less than an hour to determine that there was a vacum leak, and that it was coming from the intake manifold seal.

In any event, the throttle actuators are a known failure item on our car, especially because the early ones (like ours) had bad harnesses.

I guess it is off to my local stealer....um.....dealer.

Thanks for the help.