I've noticed something peculiar about my "new" S70 and I'm looking for some opinions. After taking my foot off the throttle when shifting, there is a lag before the engine starts to decrease in RPMs. For instance, let's say I'm shifting at 3000RPMs. I take my foot off the gas and depress the clutch, but the engine hangs at 3K for roughly two seconds before descending to the speed that I want. My 1-2 shift is pretty terrible because I just can't seem to time it right. Does anyone know why this is happening? Something to do with cruise control, perhaps? No amount of pondering has given me a clue as to how this is even physically possible unless there is a delay in the closing of the throttle plate itself.

Thanks to anyone who can shed light on this.

Tim
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Tim Smith 98 S70, 74k mi.

Probably emissions related. The emission devices are required to record
every engine mis-fire. A mis-fire (or backfire) is common when shifting
(rember older cars that did this). Since this would turn on the check
engine light (required to do so by law when an engine misfores) I bet manufactures had to be real careful about designing engine management systems that avoid backfires. Holding the throttle open probably helps to prevent a backfire with a manual transmission.

By the way, my 98 T5M does this too (but I never really noticed until
others posted here with your same observations). I guess it is "normal".

P.S. Your car should have had a new timing belt put in at 70K. Thats
an important service and should not be skipped. Just mentioning it
since you said it was "new" and if someone was selling a car with around
70K they might skip that service. A sticker is placed on the engines timing
cover (on passenger side) recording milage when the belt is changed.

Thanks for the response. I'm inclined to believe that your explanation is correct, so I'll just try to get used to it. No check engine lights have been tripped which I take to be a good thing.

As for the timing belt, it has been replaced. (Thanks for asking.) One of the reasons we bought this car is that it's been serviced by the same indy. volvo mechanic who has been taking care of our volvos for years. Along with the car came a 1/4 inch thick folder of maintenance records. The P.O. seems to have taken very good care of it.

Tim
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Tim Smith 98 S70, 74k mi.

Mine does this too, probably normal, but lets see who comes up with an explanation.

DG
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1998 S70 T5M

It's funny that you should mention this, because my '99 S70 T5M has the opposite problem, with the revs dropping too quickly. In the case of the 99 and later models, I'm sure that this is a programmable option in Bosch ME7 engine control computers, and I'm fairly convinced that Volvo didn't get it quite right in the programming revision in my car.

As for your car, which uses a prior version of a Bosch Motronic ECU and doesn't have electronic throttle control that goes with ME7, it might very well be an adjustable, mechanical control. My old Bosch L-Jetronic equipped Mazda RX-7 has such a mechanism, called a dash pot. I'm not familiar with your car's engine management, but I'd expect that there's something similar on your car.


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Jim Rothe, '99 S70 T5M,
http://www.jimrothe.com/volvo/index.html