Thread: Driveability Problem 98 Merc GM
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Old 02-02-2009, 11:33 AM
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Re: Driveability Problem 98 Merc GM
Are all spark plugs firing? In the past, I had a Coil-On-Plug fail on one of my cylinders which caused the engine to surge. Although mine ran rough at idle, too.

When you are at the 35-40MPH limit, is your engine near max RPM? If that's the case it sounds like it definitely has to do with the transmission not shifting into higher gears. 2nd gear would max out around 35-40MPH. The 4R70W transmission you have may have a bad solenoid or blocked ATF passage way preventing proper shifting. Also since the transmission is computer controlled instead of mechanically, there may be a problem with the computer shifting the transmission due to a bad speed sensor.
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