justme

I've been lurking since May in this very useful forum and now have a question. I've done some searching, but haven't found what I need. I have a 1993 300E (3.2L). When I start the car, as soon as the idle settles the ASR light comes on and the car goes into limp-home mode. This happens whether or not the car is in gear and whether or not my foot is on the brake. (The brake wear indicator light (the circle with dotted lines around it) comes on, too, but the car may well need new pads.) I replaced the wiring harness already which addressed other issues, but did not resolve this.

I've seen chatter online about the problem possibly being the
(1) throttle actuator,
(2) ABS wheel speed sensors,
(3) the brake light switch,
(4) a short in the brake lamp,
(5) floor mats interfering with the gas pedal,
(6) the engine wiring harness, or
(7) having manually moved the throttle under the hood, rather than by the gas pedal.

As far as I can tell, (3), (5), and (6) aren't problems (new switch, no mats, new harness), and (4) doesn't seem to be either. (I haven't really checked (4), but all the lights around the car seem to work fine.) That leaves (1), (2), (7), and anything else this august group may know.

Given all that, any suggestions on how to diagnose the problem? If it helps, the cruise control worked just fine in the past, but with the car in limp-home mode, I haven't had the change to confirm.

Help?

(Also, does anyone know a good Mercedes specialist in Lake County, IL?)

shadowgriffen

Number one kinda sticks out...

Silly question but, how is your trans? Any History? Could very well be stuck in gear maybe? Fluid Level on par with OEM recommendation?

Jim's500E

You should have the codes pulled from the CAN first off...could be as easy as the brake lamp switch ($20) or tough like the TA ($1200). Obviuosly a dealer can do that but a good euro-indy can also do it much cheaper if he has worked on MBs before.

A weak battery or bad alt bushings can also throw an electrical spike into the system making LH mode and cause one to look in the wrong place(s) often. Make sure those are working w/i specs. Disconnecting a speed sensor shouldn't matter.

Neutral lock-out switch also commonly is a culprit...as is the brake switch. Brake doesn't need to be pushed for the switch to malfunction BTW. Manually moving the throttle from under the hood throws the car into LH mode also. Don't do that !

justme

Thanks for your replies. The transmission seems good, although the 1-2 shift (Or is it 2-3) when starting out with a cold engine can be a bit abrupt. Like shadowgriffen, I suspect the throttle actuator, although I'm hoping for something cheaper. I'll take a look at Jim's 500E's suggestions. I had forgotten about the alternator bushings. Since I already did the forbidden by manually moving the throttle, how can I reset that? I did disconnect the battery for a while, but no improvement.

Anyway, thanks to all for any suggestions.

Jim's500E

Other than the code thrown/stored and LH mode when you manually moved the throttle from under the hood...it should have gone away the next time you started it, no? Do you have a check engine light on now?

justme

Thanks again. I don't have a check engine light on, and the problem doesn't go away after I shut down the car and restart.

By the way, you have a great car (but of course you already know that).

Jim's500E

Oh..OK I see now, its in LH mode all the time. That rots. I wish I had a spare 300E TA to lend you !

Thanks...I love my 500E, but there was a time at about 130K miles when I didn't like it too much; had a stubborn LH mode that severely dented my wallet to fix, and it did include replacing the $1200 TA ; which turns out was not the problem. It was the neutral lock-out switch on mine and both wiring harnesses were also original and shot. But its a keeper now and good for at least another 150K I'm hoping.

copley

I have exactly the same problem/symptoms with my 1994 E320 wagon.

Changed out brake switch etc. car runs perfectly yet indy mechanic says I need new Throttle Actuator.

i.e. it could go back into Limp mode at any time.


Paul

justme

For any interested, I replaced the alternator in November, which seems to have solved the problem. The alternator output tested a bit low, and ever since the replacement, the car has run fine.