My 85 380 SE recently started occasionally losing power and blowing a black cloud out the tail pipe. If I just drive with light throttle for a minute or put the trans in neutral and rev it a few times,......or sometimes just downshift or even.....just floor it..., power comes back and the black cloud out the tailpipe goes away,...........for a while,.......keeps coming and going while I drive.

Clearly is a mixture issue,.......that changes from time to time as I drive.

Anyone experienced this? Suggestions on what I can look at?

could I have a vacuum leak that is coming and going that would somehow cause this?

Brian

Four high probability causes, in roughly descending order of probability:

1. Sticking air flow meter/fuel control plunger.

2. Sticking system pressure regulator, causing fuel pressure spikes.

3. Momentary loss of electric heating power to the control pressure regulator, aka warm up regulator (WUR), allowing plunger movement in the rich direction.

4. Deterioration of a flexible hose in the fuel return line, that intermittently blocks return flow, causing a pressure spike

Frank, Can the sticking AFM fuel control plunger or system pressure regulator be "un-stuck" ? Any suggestions on how to diagnose these 4 scenarios?

I do have an 83 107 car that is running well, thinking I could possibly swap some parts around to "Test".

I had an old Warm up regulator on the shelf, I swapped it out last night,....seems worse, ,....going to try the WUR from the SL today.

Re: AFM and control plunger

First, remove the air cleaner, and move the air flow sensor plate by hand through its full range of movement, feeling carefully for any notchiness or binding. Do the bearings allow any lateral movement? Is the sensor plate centered in the bore at rest position? If there is any question about the smooth movement of the sensor, some disassembly will be in order.
Removal of the fuel distributor will allow you to check the plunger for free movement independently of the air meter. DO NOT DROP THE PLUNGER. As you lift the fuel distributor (FD) reach under it and hold the plunger in its bore. With the FD removed, you can also check the movement of the sensor plate by itself.

Also, with the FD on the bench, the pressure regulator may be opened for inspection (and the o-rings replaced).

Thanks Frank, Don't know if I want to attempt another FD removal,.....I'm on my third FD now,....there is one nut on there somewhere (can't remember where) that Has always been tough to get a wrench on fully,...and seems to me It is rounded quite a bit,...maybe a fuel line come to think of it,......as I think I recall having a fuel drip and struggling with the fastener.