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Discussion Starter · #1 ·
This is an '04 XC70 AWD with 120K miles, well-maintained. B5254T2 engine built for CA/USA.

Recently, while driving on the freeway, I noticed that when I step on the gas above 60 mph, the car lurches.
It feels like an instantaneous "kick" forward, then recoil back, each kick over with in 1/3 sec. It feels like there is an instantaneous bump in engine power (acceleration) followed immediately by a decelleration. It only happens above a certain amount of acceleration. If I switch on cruise control, and tap the "+" switch to speed up, the acceleration is very slight, and there is no kick. If I floor the gas pedal, the tranny responds properly with a kickdown into 4th. I can slowly accelerate from 60 - 80 mph using the gas pedal with no kick.

I studied and graphed some ECM parameters using my OBD-II scanner. The results shed more light on this completely repeatable engine fault that leaves no codes:

http://www.volvoxc.com/forums/showt...ot-kick-quot-during-accelerations-over-50-mph

Any thoughts on how to diagnose this problem? Anyone experienced this?
 

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Motor mounts. Start by replacing the upper and lower torque mounts with p80 platform “stiff” rubber ones.

PNs:

Upper (round with vertical pseudo solid rubber )

Hutchinson 8649597

Lower dog bone:

Hutchinson 9141042

Unlike the p2 versions these have more rubber and much less slack. Being rubber they won’t transmit realistically any more vibration.

Pretty much the issue is that your drivetrain is getting sling shotted back and forth. Since both of these mounts resist engine twist and are easy to change, start there.

Eeuroparts is the only vendor that seems to properly identify and sell the correct versions of both of these mounts based on experience so go with them.
 

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Discussion Starter · #3 · (Edited)
Problem resolution:
I guessed that the "stutter" above 50 mph was unreported misfires. I replaced plugs and coils, air filter, and cleaned throttle body. The stutter is gone.

Lesson 1: not all misfires result in throwing a DTC (I was experiencing a handful in 10 seconds).
Lesson 2: follow the PM schedule for new spark plugs & coils every 100,000 miles (mine failed at 120,000)
Lesson 3: the Bosch engine management system is a complex labyrinth of inputs and outputs -- but "computed engine load" drives spark timing,
valve timing, fuel injection timing. So, don't be surprised at a failure that appears load-dependent. My stutter only happened above 50 mph during moderate to heavy acceleration. That's the "computed load" at work varying spark timing, valve timing, and fuel injection timing at the same time spark plugs / coils getting weak.
 

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Problem resolution:
I guessed that the "stutter" above 50 mph was unreported misfires. I replaced plugs and coils, air filter, and cleaned throttle body. The stutter is gone.

Lesson 1: not all misfires result in throwing a DTC (I was experiencing a handful in 10 seconds).
Lesson 2: follow the PM schedule for new spark plugs & coils every 100,000 miles (mine failed at 120,000)
Lesson 3: the Bosch engine management system is a complex labyrinth of inputs and outputs -- but "computed engine load" drives spark timing,
valve timing, fuel injection timing. So, don't be surprised at a failure that appears load-dependent. My stutter only happened above 50 mph during moderate to heavy acceleration. That's the "computed load" at work varying spark timing, valve timing, and fuel injection timing at the same time spark plugs / coils getting weak.
Plug interval is waaaaaay shorter than that. Volvo says up to 40k for mostly highway and as low as 10k for stop and go/city/heavy acceleration. I do 20k on all the cars and they’re pretty toast at that point.
 
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