lazy electronic throttle - PeachParts Mercedes-Benz Forum

wbrian63 · #1 10-18-2007, 10:26 AM

'92 300SE. On occasion, it seems like the electronic throttle actuator is "lazy". Most of the time I drive the car very sedately, as it does very little good to flog a big beast with a little motor.

However, on occasion, I do need a little "giddy-up" off the line. (You can tell I'm from Texas...) Tromping on the throttle from stop occasionally produces a huge amount of acceleration when the car downshifts to first gear. However, most of the time, there's a noticeable lag before the motor really starts to rev.

With a high 3: rearend and a high 3: first gear, even this 2+ ton beast should move smartly off the line in first gear with big throttle.

I remember on my older cars with carburetors, they usually performed best when you didn't stomp on it off the line, but jump to about 1/2 or 2/3 throttle and floor it once moving a bit. I've tried that technique as well - same results - noticeable lag, then o-baby, hold on.

Because it occasionally rockets like I think it should, I'm thinking that maybe the throttle actuator is "lazy" - slow to react.

The last time I pulled codes on the car, I got nothing back. This problem has been persistent for the last year or so, and I've pulled codes since then, so I'm not inclined to believe that I'll find codes if I scan today.

Any suggestions for diagnosis or testing?

david s poole · #2 10-18-2007, 04:11 PM

when you are running the a/c and taking off from a stop in that car there is nothing fast about it because it takes off in second.but from your description it sounds as though the kick down is operating intermittently.i would check the cable to the trans and maybe tighten it up.

wbrian63 · #3 10-19-2007, 09:05 AM

There's no problem with the downshift. I can duplicate the problem even when shifting first to 2, which causes the car to shift to first gear, before taking off.

I know the car is noticeably peppier without the A/C on, but this is a clear case of "some times it goes, most times it don't"

That's the problem with disconnecting the throttle pedal from the butterfly. At least with a mechanical connection, I know that X amount of pedal gives me Y amount of throttle opening.

With this setup, I have no way of knowing what a given application of throttle gives me at the actuator - the computer decides what's right, and hopefully the actuator does as told.

I'm just wondering if there's a way to test the actuator to see if there are issues internally, other than pulling trouble codes.

david s poole · #4 10-19-2007, 10:37 AM

in that car you can get to the electronic accel computer thru the 38 pin connector and see what the issues are.it is rare that anything other than a failure of component will set off the cel.have someone check it out.other than that i would suggest that you do a ground check with 200ohm scale on multimeter from good ground in engine compartment to ground on engine.should not read more than 2-3ohms.the main ground from bell housing to body[under car] has been known to cause such problems as you are describing.

wbrian63 · #5 10-19-2007, 03:38 PM

Thanks, David. I'll check the ground as well as pull the codes.

The car, strangely enough, does not have a CEL. I had the cluster out recently to replace a burnt out bulb, and there is no place for a CEL.

The owner's manual shows the position of the indicator being all the way to the right on "idiot light row".

However, that part of the cluster is just dark plastic, and there's no bulb holder at that location.

Curiously, the cluster has a digital odometer & trip meter, and other 140's of this vintage I've seen have mechanical odo/trip, so obviously the cluster was replaced at some point in the past.