throttle actuator? - Page 3 - PeachParts Mercedes-Benz Forum

EricSilver · #31 05-06-2009, 10:35 AM

Don’t know if this means anything:

This morning I pumped the accelerator several times while the key and all dash lights were “On,” but before cranking. I heard the relay ping and experienced ASR fault immediately upon startup, rather than after the usual short drive time. Otherwise, it behaved as usual – when temp reached 82/83, ASR fault ended.

What I might do this weekend, if weather cooperates, is remove the coolant sensor and sit it in very hot water to heat it up before the first start of the day. If ASR fault still occurs, then the sensor is probably not the culprit. If ASR does not occur, then it probably is. My only concern is how quickly the sensor might subsequently cool down in the cold coolant, thus skewing the test.

tinypanzer · #32 05-06-2009, 09:12 PM

The temperature/resistance curves for the sensor should be posted somewhere here. I posted them once, albeit for the W126, but I would be surprised if they were different.

You could just use an ohm meter and that chart to see if the resistance corresponds to the temperature.

anziani · #33 05-07-2009, 06:50 PM

I started this thread and maybe, I have found my problem. I borrowed an OVP relay to try. That has been a week ago. So far, so good. I'll wait another week and declare victory (Ihope).
Anziani

'93 300CE
'97 E420

EricSilver · #34 05-13-2009, 12:23 PM

My new coolant temp sensor arrived yesterday – within 24 hours of ordering it from Parts Express. There is good news and bad news:

Good News: I definitely needed a new one since my fuel consumption is now sharply down, and I am not smelling fumes. I have wasted thousands of dollars on excess fuel over the past year or so because of the failed sensor. This new one will pay for itself well before my next fill-up.

Bad News: The new ECT sensor did not solve the ASR problem.

I was preparing to proceed with the brake switch replacement when another plausible cause surfaced:

About two years ago the vacuum modulator on the transmission failed. My tech plugged the line with a BB and that was that. To compensate for upshift delays I adjusted the Bowden cable -- but it turned out that what I thought was the Bowden cable was, in fact, the accelerator cable, and I set it pretty tight. I am suspecting that the tightness of the cable is not allowing the ETA to operate in a manner acceptable to the ASR computer under cold conditions.

My next course of action will be to loosen the throttle cable and see what impact, if any, that has, then thoroughly clean any visible grime from it and its hinges. Finally, I may replace the brake switch in case it too is faulty. Hopefully this will prove to be the root cause of my problem.

jcyuhn · #35 05-13-2009, 12:41 PM

Have you read this thread: http://www.peachparts.com/shopforum/showthread.php?t=88071

EricSilver · #36 05-13-2009, 12:49 PM

Quote:

Originally Posted by jcyuhn

Have you read this thread: http://www.peachparts.com/shopforum/showthread.php?t=88071

Interesting....

So when i check the tightening knob, I'll make sure the sheathing is not damaged. Thanks.

anziani · #37 05-13-2009, 02:08 PM

Eric,
I called Beckmann Technologies a month ago and told them my symptoms. I was planning on pulling and shipping my throttle actuator to them. They disagreed and said to check the throttle cable free play. It should be 1/4" They also said the throttle position switch (none on my model) and the neutral safety switch all could cause problems. I have the necessary free play and I replaced the NSS and the brake light switch. So far, every thing points to the OVP relay.
Anziani

'93 300CE 170K
'95 E420 117K

EricSilver · #38 05-13-2009, 02:21 PM

Quote:

Originally Posted by anziani

Eric,
I called Beckmann Technologies a month ago and told them my symptoms. I was planning on pulling and shipping my throttle actuator to them. They disagreed and said to check the throttle cable free play. It should be 1/4" They also said the throttle position switch (none on my model) and the neutral safety switch all could cause problems. I have the necessary free play and I replaced the NSS and the brake light switch. So far, every thing points to the OVP relay.

I am fairly certain I have little or no throttle cable free play, but it's been 2 years or so since I touched it so I don't really know. I replaced my NSS over a year ago. (It failed in Park when cold, but worked fine when hot. Intermittent ASR faults began about 3 months later. ) The current NSS is misaligned and starts only if the shifter is moved slightly to the right. I left it alone as a theft prevention feature. Brake switch has never been replaced.

This weekend I will revisit the throttle cable and other things I messed with, and set them right.

clarkz71 · #39 05-13-2009, 06:39 PM

Quote:

Originally Posted by anziani

I spent time with the Benz parts guy with my VIN but could find no exterior throttle position switch. My mechanic concurs. Is it the Throttle actuator?

Idle contact & full throttle contact are in the ETA, takes the place of the old throttle switch.

EricSilver · #40 05-15-2009, 11:08 AM

I think this will turn out to be an NSS-related problem.

As previously posted, when I replaced the old one the new one was misaligned but I ignored it. It would start in Park if I moved the shifter it a tiny bit to the right, and in Neutral if I moved the shifter a bit forward.

In the year and a half or so since I replaced the NSS, the misalignment has become more pronounced, requiring a somewhat longer rightward movement of the shifter to start in Park. I also discovered yesterday it will not start in Neutral at all – unless the car is warm (not hot, not cold) and I cycle the shifter all the way to 2, then to N, in which case it fires right up (in its normal position). I did this successfully several times to make sure it was not a fluke.

In reviewing my notes about the NSS, I saw a comment taken from member JimF’s site which said the NSS has ohmic switch contacts. If its ohmic it can be temperature sensitive and all the temperature/weather-dependent ASR fault issues I have been experiencing, and which I previously attributed to the ohmic ECT sensor, now made more sense when blamed on the completely weather-exposed NSS.

This morning I cycled the shifter several times from 2 then N to see if the car would start in N when cold, but it didn’t. However, after starting in Park, the ASR fault vanished in about three minutes, instead of the usual 5-7 (or more). Also, when the ASR fault has normally appeared, restarting would trigger limp mode immediately. Today, after shifter cycling and restarting, limp mode did not occur until after I backed out of the parking space I was in, and hit the brake. I don’t think this points to the brake switch, but rather a conflict between its signal, and that of the NSS.

So, NSS alignment is my first priority. It is as Febi switch, not OEM, so I may need to also replace it with a new OEM one in case the switch itself is faulty.

EDIT:
Also, the time span over which the variance in required rightward shifter movement increased corresponds precisely to the time span over which the low temperature ASR fault threshold has risen. In the beginning, the ASR fault occurred only in sub-freezing weather. After replacing the switch it started occurring in progressively warmer temperatures, towards its current threshold of about 55 degrees. The further misalignment is probably not natural, but more likely a result of me nudging the shifter farther than necessary when starting the car.