In the past I've posted about a rough idle only at startup for 5--10 seconds and then smooth as a kitten.
Well this morning about the third time I started it up and it didn't get smooth. It idled rough like I'm not really sure. The question and problem is a W126 89' model V-8. Does or can the fuel relay and or the fuel filter cause this. When I had a timing chain job done a few months back I asked them to change the fuel filter. I was told the fuel lines looked bad so they didn't want to take the chance and mess with changing the fuel filter. For several times I've tryed something I've never done before over the last week or so. I would turn the key on but not crank it over, just enough to work the fuel pump. Turn the key back for just a second or so and start the engine. It didn't seem to idle as rough before becoming perfectly smooth. Today it would not go away so I got on the Interstate and drove about 10 miles and when I came to a stop at the exit, it was smooth for a few seconds and then rough again like a miss. New Bosch plugs and cap rotor so I'm about 95%sure its fuel delievery problem. By the way this happens even after the car is hot and not just at cold start up. Can a bad fuel rail etc cause this problem. I've read the other threads but none seem to apply to my problem. Thanks everyone for you help and info.

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1989 420SEL 105575 miles
Pearl Black/Grey

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