Hello all,
I could use some help here. My 1998 VDP has begun to stall on me while doing 60-70 mph on the freeway. It seems to happen while decelerating. Fortunately I'm able to put into neutral while still rolling on down the road and restart it. It always restarts immediately. I'm wondering if it might be a transmission issue? Your feedback is greatly appreciated!
Thanks,
Marc

 

I've moved your post from the X350 section to the X308 section, '98 is an X308.

 

More likely a throttle body/tps problem. Even if there have been no error lights there might be a code stored or pending.

 

Thank you Cambo351 for moving my post to the correct forum. RJ, I appreciate your input and will have my mechanic check out what possible codes we can detect.
I read somewhere and now can't find the post that it could be low oil in the transmission. As you know there is no dip stick for the transmission oil on my VDP, so we'll have to get under her to check that out as well. It seems to occur when I take my foot off of our back off of the accelerator.
No warning lights by the way.
Thanks again, this gives me a new direction to look for a solution. I check back with this thread once have some results to post.
Regards,
Marc

 

Ask your mechanic to clean the throttle body throat and butterfly. A buildup of residue is often the cause of engine shutdown.

 

+1 on cleaning the throttle bore; maybe MAF sensor, as well. I think a can of good quality fuel system cleaner would be useful. Please let us know what codes your tech finds.

Doubt that it is the transmission.

 

There was a TSB affecting engines of that period.

The connectors for the throttle body had mismatched materials causing bad
connections. One side being gold plated the other being tin plated.

So check and clean the connections as a start.

There are replacement pins specified in the TSB, but they may not be available
any more.

 

Thank you all! I cleaned the throttle body and the stalling issue has gone away. I really appreciate your help.

A new issue has surfaced. The RPM's are clearly too high as I come to a stop sign. The car revs too high as it downshifts. Once I come to a complete stop, the idle speed seems to drop down to a good level at about 600-700 RPM's. But it does not smoothly downshift. Advice?

Thanks again,
Marc

 

Is it possible that you may have a vacuum leak?

 

I think the leak is quite likely. Recheck all the fittings for tightness that you took apart to clean the throttle bore and plate.

 

I had a 2005 C55 AMG and the throttle body would get clogged and the car couldnt find the idle so its defense and answer was to shut down. Before it did it would rev high, then low and then bam, engine and power off. On top of the throttle body being clogged with dirt and grime there was a vacuum leak so one made the other worse and ironically masked the other as well. That being said, now that the big problem is fixed look for a leak somewhere in that area you just disassembled.

 

I will check into all the connections surrounding the TB. Meanwhile I did add a bottle of fuel additive into the tank 3-4 days ago and it seemed to have made a big difference with the issue of the RPM's being too high as I come to a stop.
Just a big thanks to all who have helped me with this.
Take care and happy trails,
Marc