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Discussion Starter #1 (Edited)
Hello forum,

I'm trying to figure out why this 1997 C230 4 door Sedan with 160,000 miles will start then immediately "hunt" for a good idle spot. The rpm's just bounce up and down from 1000 to 1500 rpm's. I can let the car warm up to midrange temperature then turn off the ignition, start it and the rpm's will hold steady until I touch the gas pedal... just the slightest touch will set it off and then it's "hunting" for an idle. There is absolutely no other gas pedal response. If I put it in Drive or Reverse the rpm's drop to about 800 and will either hold steady or bounce and lurch. If the rpm's are steady and I hit the gas pedal it instantly starts hunting and no longer cares about the gas pedal.


When idling the car is not blowing any blue/white/black smoke. It smells just like noxious carbon dioxide. The engine mechanically sounds pretty quiet.

I'm wondering if:

a) I need to change the MAF sensor, it did receive unfiltered air for a period of time. There is traces of dirt and sand in the intake piping between the filter and throttle body plate. But no check engine light/code when plugged in.... ?
b) The absence of the TPS sensor should trip a code... right?
c) Does the TPS sensor need to be replaced? Maybe the wiring harness is providing enough of a short to tell the computer it's got the voltage it needs, if it does not trip a code.
d) Why would a computer off ebay pass ODBII scan but will not let the engine turn over? Does it require to be reprogrammed? Can I desolder the firmware chip from one circuit board and solder it to the other?
e) Why am I not receiving misfire codes, rich/lean codes, etc. when it's running and bouncing the rpms all over the place.
f) Is it in some kind of limp mode that requires a fancier computer to clear?
g) Why would a mechanic start with the crankshaft position sensor, throttle body actuator, when the fuel filter was completely clogged and the air filter had a large section caved in causing unfiltered air to be sucked in?
h) Is there a calibration necessary when replacing the battery or any components on a 1997 W202 C230?
i) Why the milage odometer will not illuminate. I can barely make out the numbers in the right light.

As soon as it warms up a couple of degrees outside I'm going to:

a) Unplug the wiring harness at the computer, unplug the TPS 5-6 pin connector and see if I can get any resistance between the wires by ohming them out.

b) Purchase some CRC cleaner and spray down the MAF sensor.


As of right now it's got no check engine light illuminated and no trouble codes
 

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1998 c230 170K
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Hi, I will try to answer some Q's. Wondering if your loosing any oil or coolant? anyway...



A) Yes, it does sound like a another MAF madness issue. If not you have a large vacuum leak somewhere, inspect all the hoses for cracks or loose fits. Not all sensors will post a code.
H) Replacing the battery does not require calibrating anything other than having your radio code handy and perhaps a window resync. done.
I) Your cluster may just need some new bulbs, would not be suprised at 160k. kinda least of your worries now.
G) Find another mechanic or DIY
D) As far as I know the other computer would have to be matched/mapped to the car and reprogrammed, I really don't know how the firmware chip could easily be pulled off the other one and I would not recommend doing so.
F) I doubt it unless you keep swapping ECU's out :p
"While changing the camshaft position sensor the clear and brown vacumn lines crumbled in my hands. I replaced the broken/missing areas with black rubber vacumn tubing" I think that should be hard tubing not the soft kind.
B
 

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Discussion Starter #3
Thanks for answering some of my questions. I put the original computer back in.

Tonight I put my voltimeter to the pins going into the ECU from the MAF sensor. I had 5, 5, and 12 volts. When running and doing the bouncing idle I had around 2 volts coming from the signal wire and into the computer. Is that enough volts? The range is 1.5 to 5 volts but what should idle be at?

I still can't trip a code by unplugging the TPS. I did not find any resistance between the wires at the ECU harness connector.

I'm wondering if the engine loom needs to be sliced open and inspected....

Everytime I start it the rpms bounce immediately. Once it's hot its more likely to hold a steady high rpm until I bump the gas pedal.
 

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Wow you have a lot of the same symptoms of my car it is such a pain when i start in mourning it dies sometimes but always runs rough idle jumps around similar to yours and it drives me crazy ive changed plugs maf with cheap aftermarket one cps egr valve fuel filter o2 sensors plug wires and other things with no help after the battery is disconnected and plugged back in it runs fine till the next day when i start car. also when gets to operating temp it runs fine but mileage is not good i'm thinking i need another maf but i've went through 3 now i'm so confused also will backfire once in mourning at startup but is mild backfire so please let me know if you figure anything out!
 

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Discussion Starter #5
Testing maf

Well....

Here are the voltage readings from the MAF sensor I found by measuring from the signal pin and ground pin going into the ECU box. I took the plastic housing off the harness connector at the ECU and was able to probe the sides of the pins.

Cold. Key on, engine off. 1.002 volts. 0 rpm

Start it up and the tach immediately bounces between 1200 and 1500 rpm. 2.10 volts
I drop it into Drive and the tach settles at 900 rpm (if I bump the gas pedal the engine will start hunting rpms up and down) At 900 rpm in Drive I had 2.05 volts.

I took the air box off after the MAF sensor junction and record 1200 rpm Park 2.04 volts. I put it in Drive and record 2.04 volts at 900 rpm.

I put my hand in front of the plastic screen on the MAF and the RPMS slow down to about 1000 rpm and the voltage drops to about 1.7 to 1.9 volts.

Now I take the MAF sensor out and douse it with CRC Electronics cleaner (no residue cleaner) Spray it for a good 30 seconds to a minute then applied a light breeze from an air compressor to dry it out.

So I took readings after the cleaning.... 2.1 volts in Neutral at 1200 rpm. solid idle not bouncing (if I touch the gas pedal it will start bouncing 1200 to 1500) It seems to hold a steady idle once it's warmed up. But the gas pedal bouncing will break the steady idle just by pressing it even the slightest.

Basically I've got 1.0 volts with engine off, key on. Then with Engine on I have 2.0 volts, regardless of the bouncing rpms, solid rpms, or the rpms.

I'm going to order a MAF sensor from AutoHauzAZ and see if that resolves my issue...
 

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Discussion Starter #6
Ready to crush this car...

Well, I replaced the MAF sensor and the car's symptoms have not changed.

Any suggestions welcome...
 

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c36, 1970 LeMans Sport, a truck
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So, you are pretty certain you don't have a vacuum leak screwing with you? Unmetered air isn't getting around anything as the car sits at idle?

MAF didn't do anything,. It smells pig rich while running-

Perhaps a cooked o2 sensor. If you are original that could very well do it. If it's slow or about dead it will keep screwing up AFR due to errors.

Could also be a temp sensor preventing car from going closed loop as well- would explain the stench.

rjp
 

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Discussion Starter #8
So, you are pretty certain you don't have a vacuum leak screwing with you? Unmetered air isn't getting around anything as the car sits at idle?


I disconnected and plugged all 4 vacuum lines coming off the intake manifold. No change. I applied vacuum to the EGR valve and it dropped the rpms by 200 rpms... In gear or out of gear. I disconnected the large purge valve vacuum line coming off the base of the throttle body, with more air coming in through that brass opening it dropped the idle about 200 rpms but it still won't change any of the main symptoms.

MAF didn't do anything,. It smells pig rich while running-


The exhaust smells like it's running a bit rich, but my garage fills up with exhaust pretty quick so it's hard to tell.

Perhaps a cooked o2 sensor. If you are original that could very well do it. If it's slow or about dead it will keep screwing up AFR due to errors.
Could also be a temp sensor preventing car from going closed loop as well- would explain the stench.


If this car needs $500 worth of sensors I'm going to start selling tickets to the bonfire.... The person before me spent way too much money trying to figure it out, gave up when mechanic said "computer problem". If I could get $500 for it at this point I'd be happy. But you are right... it could be o2 or temp sensor. What should their voltages be?
 

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c36, 1970 LeMans Sport, a truck
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Sorry, I don't have the 1st clue on their voltage ranges- I don't have the specs on either one, and frankly the O2 sensor you'll have one hell of a time checking since it mates to the main harness underneath the car, not inside like some.

Star Diagnostic can monitor O2 output voltages....Hate to say it but you might be dollars ahead taking to someone who has STAR- I suspect the last guy didn't use it.

The sensors don't actually cost that much, fortunately.

My car had drivability issues recently and no CEL- that is, until I took it out and kicked the ever living crap out of it as it tried to sputter and die- I forced it to keep running by pumping the gas.

Eventually it spit a MAF code and sure enough, it told the truth.


rjp
 

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exactly the same. no throttle response!!

my 1997 Mercedes E does the same thing touch the gas and the engine speed starts going up and down about 2 times a second 1200, 1000 over and over. i ran out of gas 4 days ago and and it did it a little then started running normal within a few seconds. then i ran out again night before last. then the battery died.. the battery died several weeks ago .. the break lights were stuck on for a week every morning i had to jump start it.. the battery capacity is shot now. but that problem with the break lights went away.. i was thinking about a new battery.. but anyway. it ran out of gas night before last and the weakened battery died before i could get it restarted... when it finally started,, the accelerator was non fictional .. you tap it and the engine starts revving 1200-1000-1200-1000 over and over.. some times it does it about variating from 2 times per second to 1 time per second. i disconnected the battery and shorted the leads with jumper cables for 30 minutes.. .. nothing i did affected it. still broken. i love my car and i know it would never do anything to hurt my feelings. but its so bad right now. i don't know if i may have to get another used one. poor poor Blacky. pray for it. i learned this morning my friends fish "Jupiter" died. i feel weakened emotionally. her cat struck out at a vagrant woman living with her who is manipulative and a paranoid delusionalist..but what homeless person is not like that. you have to understand... but my friend she is staying with is afraid they will kill her cat. but i wish luck to all the kind unfortunate people. and the other kind of unfortunate people.
can anyone tell me what part to change?
it did back-fire a few times as it was retuning out of gas.. could it have effected the throttle body? or the flapper doohicky on a hinge thingie that senses how much air it coming in?
 
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