986 Forum - The Community for Porsche Boxster & Cayman Owners - View Single Post - Heavy Engine Vibration at 900, 2k, 3k. Just replaced front moto + trans mounts. DMF?

dmboxster · 03-14-2019, 10:32 AM

Thanks for that suggestion. I'm planning on doing plugs as part of the DMF swap. It's fairly easy to replace the coils in my parking spot, so I'll do that if necessary at a different time. It's about $400 to get all new coils and I'd rather not spend the money on that unless it's necessary.

To follow up on the vibrations, the engine has been having unstable idle for a while now. It never caused these vibrations before (even with the old engine mount)

I checked the OBD and I don't see any codes or concerning issues. I did take a readout of the MAF vs Engine Speed and throttle position. Throttle position is solid at 2% during idle so that's not moving

The MAF seems to bounce around some (26-36 lbs/min) during idle. I see the engine speed bounce around between 656 and 715 RPM.

Here's my final theory. The unstable engine speed is causing the failed DMF to slam back and forth +-15mm causing the engine vibrations. As the engine accelerates one way it slams, and then as it slows down it slams the other direction causing more engine speed instability. I see engine instability at all three points (idle, 1k, 1.8k, 2.8k) which means that the slamming will be worse in those areas. Here's the kicker, because when the car is in gear there is a constant force on the DMF it can't vibrate back and forth anymore, this is why when driving I don't feel any vibrations and the idle is smooth.

I'm writing this out in hopes that someone else will read this and find it informative. Here's all what I'll be changing:

- Full clutch kit from pelican parts (includes throw out bearing, DMF, etc)
- Spark plugs (already did tubes at 55k) (DONE)
- Air filter -> [DONE]
- Clean MAF, Intake -> [DONE]
- Replace connecting hose from AOS to Intake -> [DONE]
- Replace inner rear CV joints (might as well since I'm taking them off)

03-14-2019, 10:32 AM	#4
dmboxster Registered User Join Date: Nov 2014 Location: California Posts: 17	Thanks for that suggestion. I'm planning on doing plugs as part of the DMF swap. It's fairly easy to replace the coils in my parking spot, so I'll do that if necessary at a different time. It's about $400 to get all new coils and I'd rather not spend the money on that unless it's necessary. To follow up on the vibrations, the engine has been having unstable idle for a while now. It never caused these vibrations before (even with the old engine mount) I checked the OBD and I don't see any codes or concerning issues. I did take a readout of the MAF vs Engine Speed and throttle position. Throttle position is solid at 2% during idle so that's not moving The MAF seems to bounce around some (26-36 lbs/min) during idle. I see the engine speed bounce around between 656 and 715 RPM. Here's my final theory. The unstable engine speed is causing the failed DMF to slam back and forth +-15mm causing the engine vibrations. As the engine accelerates one way it slams, and then as it slows down it slams the other direction causing more engine speed instability. I see engine instability at all three points (idle, 1k, 1.8k, 2.8k) which means that the slamming will be worse in those areas. Here's the kicker, because when the car is in gear there is a constant force on the DMF it can't vibrate back and forth anymore, this is why when driving I don't feel any vibrations and the idle is smooth. I'm writing this out in hopes that someone else will read this and find it informative. Here's all what I'll be changing: - Full clutch kit from pelican parts (includes throw out bearing, DMF, etc) - Spark plugs (already did tubes at 55k) (DONE) - Air filter -> [DONE] - Clean MAF, Intake -> [DONE] - Replace connecting hose from AOS to Intake -> [DONE] - Replace inner rear CV joints (might as well since I'm taking them off) Last edited by dmboxster; 03-25-2019 at 01:12 PM.