94 S500 Asr?? Idle Problem When Cold - PeachParts Mercedes-Benz Forum

My94S500 · #1 10-20-2007, 04:55 PM

Hi everyone! I hope this doesn't offend anyone as this is my first post and I haven't had the chance to contribute anything yet to the group (I was referred here from Benzworld). I am the very proud owner of a 94 S500 that has had the following idle issue since I picked it up about two months ago:

When cold, the car will respond to the throttle to approx. 1000RPMs and then will act as if the fuel is being cut off or it is hitting a rev limiter. It bounces between 1000 to 1600 if I keep the throttle floored. Occasionally it will "catch" and run up to 3 or 4k RPMs but only for a second or two.

When the car is acting like this, there is a different tone to the motor, almost like it is wheezing, there is a higher pitch quality to it and it sounds anemic. When the motor catches and when it is running properly, it has a much deeper sound quality to it. (I don't know if this is helpful but I'm giving all of the info I have.)

Up until last week when I started playing with various components on the car the ASR light was NOT on regardless of operating condition nor the check engine light.

The above symptoms would only occur until the vehicle reached normal operating temperature and then all would be fine. But the temp needle has to be on the next mark above "80" (I'm at work and the car isn't here so I don't recall the numerical value on the gauge) otherwise the symptoms persist.

My 94 still has the LED diagnostic code box in the motor compartment and nothing comes up when pressing the button. I am at a loss since there are no codes and I am not sure where to go from here. I am afraid to take it to the dealer as I assume they are going to assume the EA is bad and recommend replacement. If it truly is the problem then I will replace it but I am not convinced since I have read every thread I could find in regards to this and none have quite the symptoms I am describing. Also, once the car is warm it runs beautifully.

Any advice will be greatly appreciated. A solution would be great but I am really just hoping to get pointed in the right direction. Maybe someone with more experience than I have can shed some light on this?? Thanks for any and all replies!

deanyel · #2 10-20-2007, 05:05 PM

No codes on the LED doesn't mean no codes, just no codes on the DM / diagnostic module (aka pin 19). You need to build the 38 pin fault code reader and read the codes on the other pins, especially 7, but also 4, 6, 8 and 17. Try a search.

My94S500 · #3 10-21-2007, 02:54 AM

Thanks Deanyel, I don't know what I was thinking but I didn't realize each module can post its own codes. Anyways, I took your advice and built my own code-reader tonight. (I had seen this previously on K6JRF's page but like I said, I thought my built-in LED did it all.)

So anyways, I matched up the part numbers listed on his site for Radio Shack, found which store had them via Radio Shack's website and swung by after work. I went in thinking it was going to be a nightmare locating everything but I handed the clerk my paper with the part numbers and I was walking back out the door less than 5 minutes later.

Not including wire (which I already had) the grand total with tax was $16.30!! I put it together based on the schematic on K6JRF's page and it took me not quite 20 minutes to assemble the box. I can't wait to try it in the morning. I'll post whatever codes I find.

Thanks again for any and all help.

deanyel · #4 10-21-2007, 12:48 PM

You're on the right track. Since your car has ASR you should have the fault code lists as Jim's car.

Larry Delor · #5 10-21-2007, 05:04 PM

I thought I would mention, that when my ETA was bad, it would blow two fuses - one in the base module, one in the fuse box - while testing with the reader.

My94S500 · #6 10-22-2007, 01:21 AM

Well, I'm quite pleased with myself. My code-reader works just fine! (Small steps.) Here is where I am at now:

Before I had found this site I had left the battery disconnected from the last time I had "worked" on the car. I had also (not so smart, I know) fiddled with the linkage for the throttle in the engine compartment and had managed to make the ASR light illuminate at all times. Well, before I put my new reader to work I put the linkage back to where it was when I got the car and then hooked the battery back up. (I'm relaying this info not to embarrass myself but to make sure everyone has a clear picture of what is going on.)

Well, I started out using the built-in LED and this time I got code 6 which to my knowledge is "Idle speed control faulty."

This code was cleared and so far has not returned.

The most relevant code is #11 for the EA/CC/ISC module. (Pin 7.) This code is described as the following: "Closed throttle recognition signal to engine control module/ Fuel safety shut off to engine control module."

The above description makes sense based on my symptoms. The question I have now is where to go from here??

I don't know if this means I have a bad engine control module, or if there is a sensor involved somewhere or if this is just an odd symptom of the dreaded EA issue these cars seem to be known for??

Once again any advice will be greatly appreciated! (And thanks again Deanyel for the priceless advice on having more than one place to pull codes from.)

JimF · #7 10-22-2007, 10:55 AM

Have you replaced the 'wiring-harness' (w/h) on that car?? You can inspect it to see if the wires are cracked and brittle. A good place is where it ties into the MAF sensor. Loosen the connector (quarter turn) and remove it. Use a 'xacto' knife (or eq) to open the 'sheath' so you check the wires in the bundle. If OK, tape it up.

If the w/h hasn't been replaced, I suspect it's in bad shape and needs to be relpaced before you go further. A bad W/H will cause all kinds of problems.

My94S500 · #8 10-22-2007, 12:56 PM

Thanks for the reply Jim. And thanks for the wealth of information on your web site. I have not checked to see if the wiring harness has been replaced as for some reason I was under the impression that the harness issue only involved the first two years' production. (Probably wishful thinking on my part.)

I will look when I get back home this evening and let you know what I find. (By the way, if it is the harness, any thoughts on why the problem seems to go away once the engine warms up?)

Thanks again for everyones help so far.

pcmaher · #9 10-22-2007, 01:20 PM

In case you need it...

http://v12uberalles.com/throttle_actuator_rewire.htm
http://v12uberalles.com/MAF_rewire.htm

deanyel · #10 10-22-2007, 05:29 PM

I'd just clear the codes and see what comes back. Some codes could be old. Check it regularly even before any warning lights come on. Could be something with the throttle linkage - it needs a little play in it so it can return to the closed position. May well be two problems. Eratic codes would point to the wiring harness.

My94S500 · #11 10-22-2007, 06:24 PM

Deanyel, when you mentioned there should be play in the linkage to allow the throttle to return to the closed position you reminded me of something.

When looking down into the throttle body the butterfly valve never closes fully, regardless of if the vehicle is running or not. I would roughly estimate when it comes to a rest (or closed position) the valve is sitting so the leading edge (the edge facing the front of the vehicle) is cocked upwards showing a gap of no more than a millimeter or two. Is this normal operation?

Also, in terms of the linkage, I have read somewhere (not sure where as I have been going through a bunch of posts on several boards) that the cable should be tight with just a little bit of give. Mine was not and I used the black thumb wheel on the linkage to tighten the cable. However when I started the car the idle jumped up to around 1200 rpms so I loosened it back up again by a few turns and the idle returned to normal.

Like I said earlier I'm posting everything I think of to paint the clearest picture I can of what I am experiencing. Thanks again for everybody's help!

JimF · #12 10-22-2007, 07:10 PM

re: throttle opening: That's normal so looks good.

As deanyel says reset the codes and then see what comes back and back-off the linkage.

Check the w/h to see if it's ok. If not, you MUST change it otherwise it will mask 'real' problems. . . . not that a w/h problem is not real but when the wires short (as shown in Pete's pictures), you WILL, at some point, also kill an ECU.

Not sure that you have know the current ECU prices but they are astronomical; $1800 to $3500. So you don't want to kill one on-purpose.

INFO: Was able to open the Neutral Safety Switch today and see what was wrong. Posted details and pics in MENU#24.

Larry Delor · #13 10-22-2007, 08:11 PM

btw - the reason why my ETA was bad, is because it used the same inferior wire insulation that the harness uses/d. If I ever see a code 6 again, I will spit nails.

JimF · #14 10-22-2007, 08:25 PM

Quote:

Originally Posted by Larry Delor

btw - the reason why my ETA was bad, is because it used the same inferior wire insulation that the harness uses/d. If I ever see a code 6 again, I will spit nails.

. . . code 6 . . . . .

And what's funny, is that it appears so innocuous . . . . LOL

Robert Squires · #15 10-23-2007, 01:01 AM

* The symptoms you describe in your first post sound exactly like ones I had with a '93 600SEL (W140, M120). The EA/CC code turned out to be a simple cable adjustment. The main problem was an obstructed catalytic converter, the right side in this case. The obstruction became worse and worse over time; i.e. the performance didn't go bad one day and stay bad. It was on and off, irregularly. Then more often. Then finally all the time.
* In the case of this v12, the right cat was also very rusted inside. So one day, after the bad performance was constant, the exhaust back pressure blew a hole in the rusted cat, making it hiss like a steam boiler about ready to blow! Taking care of the leaking (clogged) cat also brought back the performance. The customer was impressed.