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  #1  
Old 08-09-2003, 03:20 AM
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500E limp mode and ASR

OK, as sequel to my recent lengthy series of posts about removing the throttle actuator from an M119 engine in a '93 500E, I have the TA back in the car after inspecting and cleaning it.

TA looked great internally. No signs of trouble. After re-install, I turned the engine over with the coil leads off, which is responsible practice any time that the intake has been opened. All sounded great.

Re-connected the coil leads, fired the engine up. Spotty idle at first, settled into smoothness within 30 seconds.

ASR light stayed on.

I let it warm up stationary, then gently drove it around the block. Obviously in limp mode, with ASR illuminated and poor throttle response.

When I got it back in the driveway, and shifted to Park, the idle surged rhythmically at around 1000 to 1200 RPM. Shifted back to drive, idle settled in properly. Back to Park, and surging again.

Shut down the engine and restarted. Smooth idle. ASR on again. Check Engine light on.

Pulled the positive battery terminal to reset the Check Engine light. This doesn't cure the ASR warning, which is a DTC code stored in nonvolatile memory.

Went to the diagnostic panel, found that the engine was throwing code 6, which is _Idle speed control inoperative_.

I reset that code and shut the ignition off for one minute, then restarted. Check Engine light was out. ASR light was on. Engine diagnostic is throwing a 6 code again.

Am wondering what I did to cause this, and how to get rid of it. This car has zero previous history of ASR bugginess -- the reason I removed the TA unit was because I was curious as to how well it was holding up, and wanted to get a visual inspection.

There isn't any way to force-reset ASR, is there?

s/b

-

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  #2  
Old 08-09-2003, 10:07 AM
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Ooooh, gremlins. Are you operating the throttle by hand from under the hood? That will throw a code. The idle speed contact switch at the base of the throttle pedal is a possible culprit, but I ain't no tech. It is a cheap swap-out, however. As I recall, the surging idle points to the EACM. Best thing you can do is get the Mercedes diagnostic unit on it. At least one indy here in SoCal has one. You need to watch the errors live to find the culprit. Patience and good luck!
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  #3  
Old 08-09-2003, 02:06 PM
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Quote:
Originally posted by Mark Stetson
Ooooh, gremlins. Are you operating the throttle by hand from under the hood? That will throw a code.


No, I'm not, but I hadn't known to look out for that -- thanks!

The question of throttle position is one that I do keep coming back to. One is supposed to reset the throttle stop after installing (or re-installing) the throttle actuator. But my understanding was that all you need to do is leave the ignition on for a minute or so, in order to let the computer re-learn the zero point.


Quote:

The idle speed contact switch at the base of the throttle pedal is a possible culprit, but I ain't no tech. It is a cheap swap-out, however.


Cheap swap-out? Best kind! Also fairly easy to test with a meter, I would guess.

Neutral safety switch is also possible, from what I know.

Although I continue to focus like a laser on the throttle actuator and its interface. The car ran absolutely letter-perfect before it was removed, and nothing was done to the car in between the removal and re-installation of the TA. I doubt that a switch conked out in one week of quiet sitting.


Quote:

As I recall, the surging idle points to the EACM. Best thing you can do is get the Mercedes diagnostic unit on it. At least one indy here in SoCal has one. You need to watch the errors live to find the culprit. Patience and good luck!
Darn it, I'm up north in the Bay Area.

Wasn't the guy who finally diagnosed your error issue sort of a roaming hired gun, with a rigged ThinkPad for doing field diagnostics at indy shops?

s/b
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Old 08-10-2003, 03:46 PM
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Yes, Marty of LMV INFO.

http://www.lmvind.com/

He brought in the Mercedes STAR Diagnosis System on a Think Pad. My problem turned out to be the shift positioin switch aka neutral safety switch - a $65 part. Guido's limp home problem turned out to be a brake light switch - another 60 +/- dollar part.

Check it out; they might be able to help you.
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Old 08-11-2003, 12:41 PM
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s/b- would Starmark be able to help with diag. and fix?
'
-fad
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  #6  
Old 08-11-2003, 02:54 PM
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Quote:
Originally posted by -fad
s/b- would Starmark be able to help with diag. and fix?
'
-fad
Nope. Just rolled out of Starmark about six weeks ago. Part of my rationale for removing and inspecting the TBA was the knowledge that I could no longer rely on Starmark, and that if the unit was visibly deteriorating, I should take steps to replace it preemptively myself.

Turned out that the throttle actuator unit itself looked *fantastic* internally. No wire cracking, no signs of overheating. The only point of complaint was lots of carbon on the underside of the butterfly plate, which I cleaned off meticulously.

I suspect that there may just be something simple and stupid that I'm overlooking in the re-install. I pinged TomE500 by PM and asked him about his throttle actuator re-install (by a tech). Tom helpfully dug up his notes for me.

Tom's notes say that the tech, quote, "R & R'd the Actuator then reset the Throttle Stop, Valves are OK. Cleared Faults. Runs to factory spec."

Our big mystery now is about these "valves" that the tech was referring to. The only valve on or around the TBA is the butterfly, which I guess should be checked to ensure that it pivots cleanly (this one is fine). Anyone have any light to shed on that?

On the throttle stop reset, I had had the impression that all one needed to do was to leave the car with the ignition on (but not running) for about five minutes after reassembly. This reportedly lets the computer learn the new dead-stop point of the throttle.

For fault clearing, I went to the diagnostic panel in front of the computer box. The LED there read off a 6 code when I prompted it with the input button, with no other codes in the system. I cleared the code using the button.

ASR warning still comes up instantly after ignition. If the car is driven for any distance (in limp mode) it stores another 6 code.

I'm thinking of polling the local dismantlers to see if I can find a high-mile but working TBA as a test. If I swap in one of those and the engine still throws a 6 code, that would be informative and rule out the TBA as the failure point.

On the other hand, if a boneyard unit works, that isolates the failure to the original TBA. Good as the original looks, there might be some subtle internal failure anyway. This strategy also puts the car on the road while I get a new OEM unit ordered from Phil at PartsShop.

s/b

--
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  #7  
Old 11-23-2003, 08:39 PM
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Hi Seacoast,

We need another Get-together. Meanwhile, what was the outcome of your Throttle Actuator saga? And did you find a good one from a boneyard?


Tom
92 500E
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  #8  
Old 11-24-2003, 11:15 AM
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Check out the pictures . . .

of my removed ETA. It even looked fine open but was bad!

Check out my web page (click 'www' icon below) and select MENU#24 for the symptoms and some detailed pictures.

The referecnce potentiometer looks ok but is extremely worn. Without testing it, you will never know if it's ok. 'Looks' don't mean anything.

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