Anything is possible. If you can take them out have a look at them. Have them pop tested to make sure they open at the right pressure. Id also suggest looking at the exhaust system. If you have cat converters they may be partially obstructed. High egt's and engine heat can melt them a little and cause your engine to work a little harder

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hum.....
1987 300TD 311,000M Stolen. Presumed destroyed