'86 420sel stalling

[michael cook]

Here we go again! My 86 420sel (300Kmi) runs fine occasionally, then without warning, with my foot at a steady pressure on the gas, the rpm's fluctuate between 1800 & 500, losing power steadily until it finally stalls out. Sometimes, I'll be able to 'save' it by flooring the pedal. The engine will sputter and sometimes catch, reving up to 4/5 thousand rpm before I take my foot out of it. Have heard of a couple things that could be the root of the problem, but don't want to plug-n-chug parts to fix it!
Please Help!
thank you

[jeffmg1]

Sounds like a intermittent interruption in fuel. Allmost imposible to test for. I thing fuel pump relay.