'92 300SE. 135k miles.

On occasion, the throttle on my car will "self actuate" (I think).

Here's the scenario. In many neighborhoods here in Houston, speed control "moguls" have been installed. Different than a speed bump, they're about 6" tall and 4-5 feet wide, crossing the road from curb to curb. More of a gentle "swell" in the road surface.

Intended to slow idiots that don't know you're supposed to drive slowly down residental streets.

Prior to this problem, I could easily take these bumps at 15-20mph. Now, at that speed, as the front tires cross the trailing edge of the hump, and I get the suspension compression that occurs as the nose dives down after crossing the crest, I feel a surge in the throttle and a "click" in the pedal under my right foot.

The surge is very minor, but it is definitely there. It never persists more than a fraction of a second.

It also occurs if I hit extended rough surface roads. There's a point on my daily travel to work where the road is under construction, and a trench was cut across the road about 4-5 feet wide, then refilled and temporarily patched with asphalt, which is now pock-marked with holes and undulations. Nothing that would require one to reduce speed - hit it at 35mph this AM and felt the same issue underfoot.

I've checked the throttle cable that goes from the accelerator pedal to the linkage at the front of the intake manifold and have come up with nothing. Everything looks fine and is tight. Manual operation (key off) of the linkage shows free movement - no binding.

Engine mounts are fairly new (<15k) old.

I've not checked trouble codes. That is my next step.

Any ideas or suggestions?

Last night, I pulled codes on the EA (electronic accelerator) module. Got 3 ,6 and 11. Only 6 ties to anything in the diagnostic charts, and what that points to is more than I can tackle myself, as it requires a breakout box to further isolate what's failed. I think in all failure cases, it points to the EA being faulty.

Before I pulled the codes, removed the air cleaner and with the engine running, I pressed sharply down on the radiator support. I was "rewarded" with a strong "blip" of the throttle coming from the EA. Did it several more times - same result each time.

Pulled codes and attempted the same test again - no blip when I bounced the front of the car.

Note to all that might try this - hold the hood up when you do - I nearly konked myself on the noggin when the hood started to close after the first strong bounce.

Does anyone have any ideas???

Does the car have ASR?

The code 6 points to an issue with the neutral safety switch. I would start with there!

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car does not have asr.

Neutral safety switch attaches to outside of transmission, correct?

I was looking at the wrong column when I indicated that only code 6 mapped.

Using a impulse counter tool, code 3 points to a whole host of problems with the CC/ISC actuator (which is what AllData says I have if the car does not have ASR). To wit: CC/ISC actuator, Throttle valve actual valve potentiometer, drive actual value potentiometer, safety contact switch, closed throttle recognition switch, CC/ISC actuator (voltage supply), reset not accomplished (actuator adaption).

Code 7 links to message rec'd from the CAN databus: message from CC/ISC control module (N4/3) faulty, or Reception from LH-SFI control module (N3/1) faulty.

Code 11 is either Fuel safety shut-off signal to LH-SFI control module or Closed throttle recognition signal to LH-SFI control module.

Code 3 suggests erasing the code, turning the ignition off, turning the ignition on for at least 90 seconds and checking for the code again. If the code reappears, the CC/ISC actuator should be replaced.

The test procedures beyond each of the trouble codes all involve a breakout box to test values at various pins on connectors in the system, or even a signal generator to test throttle plate movement. None of these are doable by me.

Am I risking life and limb driving the car? Will I experience a catastrophic failure involving unintended acceleration?

Any input is appreciated.

On your car w/o ASR the throttle actuator controlls ONLY the idle & cruise control functions. Idle control happens any time your foot isn't on the pedal.

Should not have any other throttle control function.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Have you looked at the insulation on the wires in the wire harness for the EA? They may be toast. You can rewire it pretty easily though.

I've not checked the wires in the harness for the EA. The car has an updated engine harness, but I don't know if that includes the EA. I'll check all of the wires coming to the EA.

Since this behavior is triggered by "relatively violent" suspension travel, I'm thinking there are wires somewhere coming into contact when they shouldn't.

Normal cruise is never effected - just things like over speed bumps, big dips in the road, rough or undulating pavement around 20mph or less, etc. Something's getting wiggled and is mis-behaving.

I'm not beyond rewiring the EA if that's what it comes to. Just checked the part at MB and it's $1760 list.

The EA wiring is separate from the engine harness. It is my understanding that all early M104s had wiriing issues in both the engine harness and the EA. I have rewired 3 EA's to date for E320 and 300E models. If you can get to the cable that runs into your EA and cut a 2-3" slice in the outer sheathing, you can tell if the insulation on the wires inside is flaking.

I wrote a rewiring tutorial for the M104's and posted it on benzworld. I did'n post it here because I couldn't make the .pdf small enough with the illustrations to meet the upload criteria for this site.

Thanks - I've read the tutorial. Easy as pie for someone with reasonable skills.

Best thing is that the removal process for the actuator on a '92 300SE is about 5 minutes work. There's no crossover tube - the air cleaner is an old carburetor-style unit that sits right on top of the MAF which is connected to the EA on the driver's side of the engine...

I'll let you know what I find.

Regards

Good Deal

Let us know how it goes.

Sorry for the long post, but I've got a lot to report...

Pulled the actuator off on Friday evening. This one's not like any of the one's I've seen in any rebuild article. One side has the cover as seen on others, where the control motor and electronics are. The other side has another cover and a lever where the throttle linkage connects. This lever is mechanically attached to the throttle shaft, turning the lever opens the butterfly.

First - like all (I think) M104's, it's on the driver's side of the motor. However, the cable connects to a receptical on the passenger side inner fender just behind the passenger headlamp, so the cable is a "bit long". It goes from the actuator left toward the front of the motor and then u-turns to run parallel to the injector rail, then up into the cable conduit at the forward firewall, across the engine compartment and down to the receptical.

Removal is a 10-minute job, most of which is the struggle to remove the air cleaner...

Got it out and slit the covering near the connector. Didn't see what I expected, which was rotted/degrading insulation. Fiddled and piddled with the wires a bit to see if I could get some of the insulation to flake off. Nothing telling, although with strong persuasion, I did get a little damage. Figured if I could damage the insulation at the plug end, where the temps are relatively cool, that things can't be good over by the actuator trapped up under the air cleaner in the bowels of the engine compartment.

So I slit the cable from end to end, starting about 1" from the connector and stopping about 1" from the actuator.

EVERYTHING WAS AS NEW... I couldn't find one thing wrong with the insulation anywhere. Bending and flexing individual wires had no effect on the integrity of the insulation.

OK - cable is OK, but that doesn't mean there's not something bad down inside. Got the cover off on the side that contains the motor and circuit board. Removed the primary gear without issue. The throttle shaft runs through what appears to be a rheostat-combo-return-spring device. Never could figure out how to get that sucker off the throttle shaft. Wires and visible electronics appear to be fine. No smell of burnt anything, just grease.

Put the cover back on. Then remove the cover and reinstall the primary gear... Replace cover again.

To seal the cable, I used some vinyl tape I've used before to re-wrap other wires on the car - it has no adhesive, but is somewhat stretchy like cling wrap. It's installed in places on the car that are at least as hot as where this cable will run, and has been there for several years. For further protection, I used some corrugated tube "conduit" like you see on domestic cars everywhere. It's black, and the diameter was such that it was a glove fit over the cable. I think my biggest worry is moisture infiltration, but the path the cable takes, plus the extra covering should ensure a dry cable for the forseeable future.

One thing I did notice was that the throttle plate (butterfly) and the bore of the actuator below the butterfly were really nasty. Car has 140,000 miles (wasn't right # in original posting), and I don't think has ever been cleaned in this area. It has some blowby, but not excessive for the age. Wasn't well cared for before I got it. Anyway - carb cleaner and a toothbrush got all that in working order.

Reinstalled actuator, MAF, etc and started car. Ran normally.

Did notice that when you turn the key, the throttle momentarily snaps to full open and returns to idle. I "think" this is a new behavior. I'm pretty sure I've always heard a strong click when the key is turned to position 2, but now if I touch the throttle gently (not enough to actually open the butterfly, there's a linkage-designed free-play range of motion), I can feel the brief open-shut action. Total cycle time is half-second or less.

Didn't drive the car, just verified that it ran. Got it up to temp - bounced fairly rigorously on the bumper - no blip. Changed the oil and rotated tires.

Start the car this AM to go to work - idle is WAY too low - 500 or less on the tach when in gear, but that doesn't persist after I back of the driveway. Car seems to run fine, but now I've got no 5th gear in the transmission!!! Cruise-control is also inoperative.

I did take a route that usually results in the throttle blip behavior, and it behaved flawlessly.

I've checked ALLData, and there doesn't seem to be any thing about adaption of the actuator, although it's indicated that you can reset some values to "mean" by clearing all codes and holding start button down on impulse counter for 6-8 seconds after receiving the one-blink (no codes stored) indicator.

I'm thinking that no 5th gear and no cruise control are related.

Any suggestions now?

Checked codes last night. Same set for the EA/CC, 3, 6 and 11. Checked TCM (trans control) - code 4 (I think) - description is CANBUS communication with EA/CC distorted. That explains why I've got no 5th. If the transmission can't communicate with the throttle, it probably denies 5th gear.

The CC being inop is probably related to the problem that's causing the TCM to complain about the CANBUS.

I've verified that the brief full-throttle activity at key-on is new, as yesterday I felt it under my foot on the throttle - never have felt that before.

Erased all the codes for the EA/CC. Shut key off, and turned it back on. Checked 2 minutes later and #3 is back again.

Couldn't erase #4 from the TCM. I'm guessing as soon as it's gone, it comes back again.

I guess my rooting around in the throttle actuator has messed something up. I can't see how opening the harness would have any effect, especially when the wires are pristeen and I didn't cut anything.

I know where there's a 93/94 S320 that's wrecked. I'm gonna check EPC to see if the part #'s are the same and see if I can strike a deal for the used actuator. Lots better than the $1,400 I'm facing at the dealer.

UGH.

After the fiasco of checking the actuator wiring harness and having more problems after reinstalling, I solved the problem...

I bought another car.

Not to worry, I didn't give up on the 300SE. Just knew of a wrecked '93 at a repair shop near by. Called the shop to see about getting that part and the owner pestered me to by the whole car. I'd gotten some parts previously (trim items) off this car, and he'd wanted to sell it then for $2,000.

I paid $1250 delivered to a buddy's repair garage where I can have access to a lift for disassembly.

Pulled the actuator off, cleaned it up and installed it. Turned the key - no more full throttle blip at key-on. Buttoned everything up and took it for a spin - 5th gear is back, and so is the cruise control!

Pulled codes for the EA/CC, and still had the #3 error, but I think that was from the previous actuator. Erased that code. Code #6 is still there as well, so I'm going to check the adjustment of the neutral safety switch and replace it if required to see if we can get rid of the code. I erased the code and will check later to see if it comes back before I make the effort on the NSS.

This AM, I hit the same spots in the road that had previously plagued me with throttle blips - not a peep out of the "new" actuator.

So, my cost on a new actuator would have been $1524 with tax. The way I look at it, I'm already ahead to the tune of $274...

Best part of the deal - the car came complete with a newly rebuilt-by-Mercedes transmission with about 8,000 miles on it.

Never parted a car out before - now's my chance.

Thanks to all that have contributed suggestions to this effort.

Good detective work . . and even better financial deal.

ETA's are really a PITA.

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Regards . . . . JimF
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'94 S500 Cpe

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