528E with major sputters (sometimes)

[BMWROSS@xxxxxxx]

I'm trying to resolve a problem with the wife's 84 528E. After about an hour 
of highway driving it can develop a significant stumble. Significant like 
it's undriveable. It defenitely feels like a fuel starvation problem, exactly 
as though you were running out of gas. Also, long uphills could  be the 
trigger, it's hard to tell, but it seems there may be a relationship. 
Stopping and idling for a few minutes will make it go away, although the last 
time it did this it wouldn't idle in drive for a day or so afterwards. Now 
it's back to normal. She rarely drives far, so this has only happened ~3 
times over the last 12 months. 

A mechanic suggested replacing the fuel pump relay. Now that I've identified 
which it is, it turns out that that was replaced recently along with the main 
DME relay. So that's not it. Any suggestions? 

The third relay in the series outside the fusebox  is missing, I believe 
that's for the 02 sensor heater. Since the car has a one wire 02 sensor. I 
guess that makes sense. Also, the fuse box shows something called a relief 
relay. What the heck is that? 

Any comments on the above would be most appreciated. 

Ross 

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