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Old 09-07-2001, 09:40 AM
Posts: n/a
Idles smooth when cold and then starts to get rough(not a regular miss like a cylinder not firing but erratic missing) as it heats up with idle changing ( not quite a surging but a slow up and down in the idle (600 rpm to 900 rpm) with random missing at irregular intervals which seems like a missing spark plug?? This is what I had on my '88 560 SEL. Drove me nuts. Changed spark plugs, wires, distributor cap, rotor, checked for vacuum leaks, did compression test -- everything. No difference. I have 180,000 miles on mine. What mine turned out to be was dirt in the metal screens in the fuel distributor that the lines to the injectors hook up to. Injector cleaners helped for a short term( not perfect, but better)-car idled smoother after being on highway with injector cleaner and got worse with city driving. The cause???? Rusted fuel lines from the gas tank! When we changed the two lines (feed and return) the feed line broke in two - it was so rusted. Changing the lines and pulling out the screens in the fuel distributor and cleaning them and re-inserting them finally cured the problem. Don't know if this is your problem -it was mine and drove me nuts for a year and a half before we found it!!!
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