93 300E M104 Idle & Stalling Problem

I have a 1993 300E 3.2 M104 engine that recently started acting up on me. When I start the car cold, it starts and idles fine but after about a minute or 2 the idle races and cycles between 5K-15K RPM
cycling in 1 or 2 second intervals then the idle becomes rough and the engine eventually stalls after 5 seconds of rough idle. Then when I restart the engine, I get a rough idle then it stalls immediately. Here is what I have done to try and correct or diagnose the problem so far:
1. checked fuel pump relay (fine) 2. fuel pump noise is audible when ignition is turned on 3. checked spark plug (strong spark detected during crank) 4. replaced OVP (did not solve the problem) 5. visually inspected vacumm hoses within engine compartment (all's fine) 6. the car is still sitting in my garage - undriveable...
If anyone can help with suggestions with my diagnosis, i'll appreciate any input. Thanks in advance.
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No codes??
I'd suggest the MAS (mass air sensor) is the prime suspect. But first check that all the air duct is tight - from the air filter to the clamp on the engine's air intake.
I had a "check engine" incident with my E320 - looked at the codes - learned nothing - took it to dealer for diagnosis. MAS - $500. Declined their generous offer and drove home. Removed the MAS and found a bit of dirt on its mesh and very very carefully cleaned it's elements with a (smoker's) pipe cleaner.
So far so good.
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sorry no codes. i have no experience in extracting or reading fault codes. can you tell me where the MAS is located? i'd like to try your solution to see if it will solve my problem. thanks for your help.
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The MAS (mass air sensor a/k/a air mass meter) is located in the intake air duct after the engine's air filter - it has a wire harness attached to it. It measures the volume of air entering the engine so the fuel injection can supply the appropriate quantity of fuel for that air volume.
Do a Google search to learn how it works generally and then be CAREFUL when doing anything with its elements. A new one costs approx. $300 - shop on line for one if it comes to that. And yours, being older, may be defective, not impeded by a bit of dirt as mine was.
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i just took it out and looked at replacement units online. thanks for walking me through it. i saw some remanufactured ones for $130.00 - $180.00 and the new bosch replacement units ranges from $300.00 - $400.00.
whew! i am so tempted to replace it immediately but considering the cost of a replacement unit and the risk wasting money, is there a simple way for me to check if my current unit is really defective? sorry, i don't mean to sound cheap or anything like that. i just don't want to get stuck with a $350.00 part that i don't really need. i hope you understand.
thanks again for being patient with me.
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You're not being cheap, just prudent not to replace an expensive part unless it's found to be defective. (You also see the reason for caution when doing anything with it.)
Some here, smarter than I am, know how to check these with an ohm meter. Suggest you create a new post titled "How can I check my Air Mass Sensor?" or similar.
Exactly specify the engine # 104.???
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Shouldn't the "check engine" light come on if the sensor was out of range? It's sort of odd that your engine is running as poorly as it is without the computer detecting a fault.
Josh

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okay, i'll take your advise and post a new topic specific to MAS testing.
i also agree with Josh regarding the computer not picking up a fault (check engine light) with the condition of the engine. that's kind of odd. perhaps my problem is in the fuel delivery system (fuel pump, fuel filter, etc.)? i already tested the fuel pump relay with jumpers and the fuel pump is very audible upon starup so i'm assuming it's okay but i could be wrong. i'm not sure how to difintively test the fuel pump in order to rule it out of the equation.
in any case, i would like to express my gratitude to both of you for your inputs and suggestions. i'll keep you posted on my progress. thank you very much.
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There are members of this forum with much greater expertise than mine, but I don't think that the MAS is the issue unless you are getting a fault code nor does it sound like fuel delivery (I wouldn't expect the engine to rev up if fuel starvation was occurring). It does sound like air starvation (hence comments about the MAS), but voltage being out of range should cause a fault code *unless* the MAS is just bad (e.g. voltage is within range but it's just giving the wrong voltage for the current airflow volume). Out of curiosity have checked to ensure that there isn't any blockage along the air intake (clean filter, no obstructions, etc.)? If it's clear, see if you can get flash codes off the computer (I think that this car has them) since you can't get it running long enough to drive it to a shop or some place like Autozone. To do so, go to the scanner port (should be near the battery) and hold the button for 2 - 3 seconds to start to read codes. Reading codes involves just counting the times the LED blinks. Then hit the button for 2 - 3 seconds to get the next code, and continue until the first one repeats. When you want to clear them, hold the push-button for more than six seconds. Once you get the codes these can be correlated to diagnostic documents.
Josh
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thanks for staying with me Josh. i checked the air intake path (from filter to throttle body) and all seems fine (no blockage found). the air filter is a bit dirty but nothing major to obstruct air flow. i also started the car this morning and it started with normal idle (i thought it fixed itself for a minute there!) but when it reached normal operating temperature (about 3 mins. of smooth idling), it started to idle rough again and eventually stalled after a minute. then it just stalls with rough idling during subsequent starting attempts.
i tried your suggestion with the scanner port LED reading. here's what happens:
ignition off: i hold the button down for 3-4 seconds but the LED does not light at all. ingnition on: i hold the button down and the LED immediately stays lit (does not blink) the whole time (2-4 secs) i'm depressing the button. no blinking of any kind even after holding the button down longer. the LED stays on when the button is depressed and off when the button is released.
any ideas why? thanks.
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I think that it's telling you that all is well as far as fault codes. Now what is interesting is that it ran fine until it warmed up. I seem to recall that the O2 sensor (which applies voltage between .5v and 1.0v) doesn't start doing anything until it is warm. Perhaps the O2 sensor is sending voltage within range but the voltage is wrong for the given conditions.
Another item to check is your fuel filter. Perhaps it is getting clogged and starving the engine. And hopefully this isn't a notorious wiring harness issue (I can't recall the years that MB used the bio-degradable insulation, but it was mid-90s). But all of this is just guessing. I suggest you see about having the car towed to a local (independent) MB shop. The cost of the tow could be less than one wrong guess. Depending on where you are some of the folks on this forum could offer a suggestion on where to take it.
Josh
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This is a multi-part message in MIME format. --------------020200030702000700000706 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit
i also started the car this morning and it started with normal idle (i thought it fixed itself for a minute there!) *but when it reached normal operating temperature (about 3 mins. of smooth idling), it started to idle rough again and eventually stalled after a minute.* then it just stalls with rough idling during subsequent starting attempts.
This suggests a temperature related fault. The engine's temperature sensor is on the thermostat - right by the oil dip stick. Check if it's properly connected.
--------------020200030702000700000706 Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <meta content="text/html;charset=ISO-8859-1" http-equiv="Content-Type"> <title></title> </head> <body bgcolor="#ffffff" text="#000000"> <pre wrap=""> i also started the car this morning and it started with normal idle (i thought it fixed itself for a minute there!) <b>but when it reached normal operating temperature (about 3 mins. of smooth idling), it started to idle rough again and eventually stalled after a minute.</b> then it just stalls with rough idling during subsequent starting attempts.
This suggests a temperature related fault. The engine's temperature sensor is on the thermostat - right by the oil dip stick. Check if it's properly connected.
</pre> </body> </html>
--------------020200030702000700000706--
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there are 2 sensors on the thermostat housing both of which are snug and properly connected T.G. thanks for the tip. but when i started the car cold again, during the 2-3 minute smooth idle, i was able to get a reading from the diagnostic port and here's what i got when i depressed the button for 2-3 seconds as Josh suggested:
1st push - 8 LED blinks 2nd push - 10 LED blinks 3rd push - 10 LED blinks 4th push - 10 LED blinks then the motor stalled
how do i make sense of this reading? any thoughts? thanks.
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Haven't a clue about those flash codes, sorry. Perhaps Josh will know.
Tom
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After I thought a bit more about the engine's behavior I'd start to zero in on the O2 sensor, especially if it's NOT in the control chain during warm up. I'd see what happens if its unplugged - or better, do an internet search, - some on line shops specialize in these sensors and may have descriptions of behavior during O2 malfunctions.
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thanks TG. after reading your suggestion, i searched the web for some info and found a very interesting article that points to the O2 sensor as the culprit here. based on the flash codes i got from Josh's tip, this article shows a DTC-5 table (94 E320 same engine as mine) that indicates 10 flashes as an O2 sensor problem so i think you're on the right track.
here's the link:
http://autorepair.about.com/bl119i.htm
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All knowledge is found on the web!
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It will be in another hundred years or so...
Don't hold your breath :~) Marty
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Martin Joseph wrote:

Unfortunately, Google says it'll take them another 300+ years to index it so you can *find* the info you want. :-/
http://www.theinquirer.net/?article &803
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Good luck - and let us know if this fixes the problem.
Josh

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