94 C280 Engine Stumbles - Fuel, Vacuum, or Electrical???

[bbogner12]

If you've read any of my previous posts you'll find I bought a basket case that didn't run. After owning the car for a month the car now is back to running form. It starts, runs, and drives. The problem is I've got something causing the engine to hesitate when pressing the accelerator.

The car starts from a cold start and sounds great. Shortly after starting the car begins to surge. It will fluctuate between 500RPMs and 1200RPMs. I've checked for vacuum leaks and all hoses appear to be connected. Once the car is warm, it seems like the idle levels out and stays around 1000RPMs. Placing the car in reverse or drive, the RPMs fall to 600RPMs.

This is where things get weird. As you try and rev the accelerator (while sitting in park), it will stutter and backfire. It will eventually pickup and then rev properly. When I'm heading down the road I can run the car up and then once the RPMs fall it will hesitate before picking back up acceleration. It doesn't happen every time, but it is pretty consistent.

Is this due to bad fuel? Possibly fuel pressure regulation issue? The question is, what should appropriate fuel pressure be at the rail? It could also possibly be the fuel filter...

Another option is it could be a crack in one of the vacuum lines. Any suggestions on how to test this theory without replacing each line?

The third is there are possible wire with insulation issues. While I don't think this is it the issue, I'm not ruling it out since I did replace the harness for the ABS/ASR system. Which means it is possible other parts of the harness are causing a problem. Upon inspection I didn't see anything.

Any help is appreciated.

Brian