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Engine Pulse Vibration

Help, Advice and DIY Tutorials on Volvo's P80 platform cars -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.

1992 - 1997 850, including 850 R, 850 T-5R, 850 T-5, 850 GLT
1997 - 2000 S70, S70 AWD
1997 - 2000 V70, V70 AWD
1997 - 2000 V70-XC
1997 - 2004 C70
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ZionXIX
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Year and Model: 1996 850 Turbo S/W
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Engine Pulse Vibration

Post by ZionXIX »

For the passed week I've noticed an odd "pulse/vibration/studder/surge?" Coming from the engine at idle. While sitting idle I can feel a random vibrational pulse through the entire vehicle including steering wheel and seat. Sometimes I feel it once every 30 seconds and sometimes multiple times in rapid succession. The tachometer never changes. RPM confirmed through OBDII reader. Stays right at 800 or 840. No CEL, no stored codes. Happens independent of AC engagement. Its too subtle for i misfire i would think. Its very strange. Although I've never heard what detonation sounds like, it's on the list?

Thoughts?
Scarlett: 1996 850 Turbo Wagon in Reagent Red Pearl ~210K mi
Norman: 2012 F150 XLT Crew Cab in Oxford White ~110K mi
Ember: 2005 XC90 2.5T FWD in Ruby Red Metallic ~83K mi *Newest addition to the fleet*
Ruby: 1997 850 Turbo Wagon in Reagent Red Pearl - parts car
Rose: 2020 Ram 1500 in Delmonico Red Pearl - SWMBO's Vehicle
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RickHaleParker
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Post by RickHaleParker »

Check for DTC codes.
Clean out the IAC Valve ( Idle Air Control Valve ).
Check for Air leaks in the Intake side.
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1998 C70, B5234T3, 16T, AW50-42, Bosch Motronic 4.4, Special Edition package.
2003 S40, B4204T3, 14T twin scroll AW55-50/51SN, Siemens EMS 2000.
2004 S60R, B8444S TF80 AWD. Yamaha V8 conversion
2005 XC90 T6 Executive, B6294T, 4T65 AWD, Bosch Motronic 7.0.
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ZionXIX
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Year and Model: 1996 850 Turbo S/W
Location: Texas
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Post by ZionXIX »

Codes are clear
I just replaced the intake hose attached to the throttle and the IAC a few weeks ago. It was very clean inside. I guess I need to find my rigged smoke tester for the intake.
Scarlett: 1996 850 Turbo Wagon in Reagent Red Pearl ~210K mi
Norman: 2012 F150 XLT Crew Cab in Oxford White ~110K mi
Ember: 2005 XC90 2.5T FWD in Ruby Red Metallic ~83K mi *Newest addition to the fleet*
Ruby: 1997 850 Turbo Wagon in Reagent Red Pearl - parts car
Rose: 2020 Ram 1500 in Delmonico Red Pearl - SWMBO's Vehicle
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