300SE stalls and dies, then starts right up and runs fine???

[andrew6981]

First - '88 300SE, approx 236k miles, name of Gertrude
So recently I replaced my fuel filter with a Fram G3737, did the Air Filter, and just put new exhaust on. It wasn't factory exhaust I used to replace it with. We replaced the 2 mufflers with similar (but not identical) ones, both of them being dual in/dual out. I have also noticed that she doesn't like to rev very easily any more. When I stomp on the gas, it takes about 2 seconds before she actually starts to rev, and it almost feels like the power of a 4cyl. It's running on all 6, but doesn't feel powerful really...
Here's where i first noticed the problem: I was driving home over the pass after Thanksgiving and there was about 6 inches of snow and slush on the road. Coming down, I was doing about 30-35mph, and when the roads started to clear I tried to accelerate. She had been basically idling since the top of the pass (about 6 miles or so) since I was going downhill and at a fairly low speed. I pressed the pedal, and nothing happened at all. I kept pressing and trying to go, but it seemed as though it was getting pretty much no fuel, and the more throttle I gave it, the leaner it ran, and tried to die. After a few moments of this, she did die. I put her in neutral, still coasting (by now about 50mph) and tried to start her up again. She fired up, and I was able to rev her up to about 4k before it seemed as though there was no more fuel. I did this several times. Thinking it was perhaps the fuel pump or something related, I tried this again, but as soon as she revved a bit I turned the key off and then started her right back up. This seemed to actually keep her running right, but not for more than 5-8 seconds. Since I was down out of the mountains and about in the area of North Bend (outside Seattle on I-90) I was losing my coasting speed, and was only going about 20 by this time. I pulled onto the shoulder and kept coasting as much as I could, trying to get her alive again, but seemingly to no avail. All of a sudden, in doing this 'start-rev-shutoff (repeat)' process, something came alive again, and she fired up and stayed running. Drove the rest of the way home with no problems. Now though, this is happening almost every time I get in the car after letting it sit for awhile. I'll go to the parking lot after work, start her up, and she'll cough sputter and die. I try to rev her but I can't. So, i'll shut the key off, start it up again, and rev her up to about 4k or so when she starts. This seems to work fine, until I've let her sit again. The performance still isn't what I think it should be (what it was 2-3 weeks ago) though...
I was thinking perhaps the new exhaust is too restrictive (since the front muffler is actualy a muffler, and not just a silencer) or maybe a bad throttle position sensor? I tried tapping the fuel pump relay but nothing changed...when I pulled the relay out she died immediately.
Gertrude and I need your help!!!

[andrew6981]

Somebody?!? Anybody?!? I'm getting really frustrated (and worried) here...pleeeeeeeeease help if you can!

[jdc1244a]

Look through these for some ideas. You know it takes time for people to respond. You can also search “stall� in the 124 forum – 99.9 percent of them have the M103.

http://benzworld.org/forums/forums/thread-view.asp?tid=1185911&posts=4&hl=stalls

[WhiteSEC560]

This happens with mine too and I finally figured it out.
It has to do with fuel line pressure. The fuel senders don't keep the lines pressurized well after a long tim (i.e. 15 years) and the gas slowly drips back into the tank.
When I turn my car over, I turn on the electrical but I don't crank the engine for about 5 seconds, its gives the electric senders enoughtime to pressurize the lines with fuel.
As a side note the angle at which the car is parked also factors into this.
I do this with my SEC and have had no more of the stalling your discribing hope this helps