BenzWorld Junior Member
Date registered: Nov 2008
Vehicle: 1988 260E
Location: Palm Beach, FL
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What's happening?? Car runs rough after prolonged hi-speeds
I really need help from you experts on a problem with my 124. The car normally runs beautifully under all conditions; idles fine, accelerates without hesitation or stumbling, pulls strong, shifts cleanly, runs all day long at 80 mph. Cold starts sometimes crank longer, but that's the only weakness. 193K miles on the clock.
Now the problem: last weekend made a 6-hour high-speed trip on Interstates, cruising for several hours at a time at sustained 75-80 mph. Pulled off for gas stop, and as soon as I'm on surface streets at low speed, particularly stopped at traffic signals, the engine idles very rough (RPMs go below 500), to the point that I have to keep light pressure on accelerator to keep it running, and it stumbles badly trying to accelerate from a stop. Accelerating, car is very sluggish, totally under-powered. Shut the engine off, even just long enough to fuel-up, and it starts up and runs fine again in every respect. Run along at 75 mph for a few more hours, slow down in town and the rough idle/sluggish acceleration returns. All it seems to take to get rid of the problem is to turn the engine off for even just a few minutes. Problem never exists if I just drive around town, only after prolonged high-speed driving.
Recent (within past 2,500 miles) maintenance/service performed: new OVP, new battery, all new filters, all fresh fluids, new correct NGK non-resistor plugs. Routine maintenance has always been performed. No obvious evidence of vacuum leaks ("economy" gauge usually pegged left at idle, except with A/C running, when it rides about quarter way). No CEL. What do you make of this situation? Thanks guys.
1988 260E (Anthracite Grey over Palomino)
Owned since new; still strong and smooth @ 197K
Last edited by Cal Learner; 03-16-2009 at 07:12 AM.