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

dmboxster · 03-13-2019, 02:01 PM

Issue:
Heavy Engine vibrations at 900-1.1k, 2k, and 3k while in idle. No vibrations when in gear.

Parts already replaced:
- Transmission mount
- Engine mount
- Spark plugs
- Spark plug coils
- Air filter
- Cleaned MAF

Left to do:
- Run smoke test on intake
- Replace MAF if necessary
- Replace DMF if vibrations are still present
- Solve world hunger

Brian in Tucson · 03-14-2019, 07:37 AM

Do a comprehensive tune up, plugs, coils, etc. (tubes if they're leaking)

dmboxster · 03-14-2019, 09:13 AM

{ removing dupe }

dmboxster · 03-14-2019, 09:32 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)

flete25 · 03-14-2019, 10:36 AM

I had a similar issue...I checked the coils and 3 of them were cracked .I replaced them along with the plugs and problem was solved.

dmboxster · 03-14-2019, 05:55 PM

I'll give replacing the all the plugs and the coils. The car's got 90k on it and I doubt the coils have ever been replaced. If this doesn't work then I'll try the DMF.

Geof3 · 03-14-2019, 09:46 PM

What transmission and motor mounts did you use?

dmboxster · 03-15-2019, 09:46 AM

The transmission mounts are Rein Automotive. The engine mount is a Lemfoerder. It was pressed into the original bracket in the correct orientation.

Before the updated mounts the entire car was shaking. It’s noticeably better now. There’s just continued vibrations.

The parts are ordered and should be here next week. I’ll update after I install the coils + plugs and clean the intake, MAF

dmboxster · 03-25-2019, 12:08 PM

Did the tuneup. Replaced all plugs, spark coils, did oil change. Plugs all looked evenly worn with even deposits on the tips. Coils were in good condition but I replaced them anyway. Cleaned the MAF, replaced engine air filter. Engine pulls better now, and is a bit smoother when shifting.

However, the tuneup made no difference in the vibrations or random engine speed.

I was able to pull the long term trim values for the engine and they are at ~+12-13%. This indicates that the MAF is weak, or there’s an air leak somewhere. Tried running with the MAF unplugged and took a short trip. This seemed to stabilize the idle speed and car ran well without it. After plugging back in the engine again was not settling on an idle speed and having weird behaviors. I replaced the MAF with a genuine Porsche Bosch sensor at about 60K miles. A little upset that the $300+ calibrated sensor has a life of 30k miles. Cleaning it had no effect and my trims are still high. Still have same vibrations with MAF connected or disconnected. Will do a smoke test to check for any air leaks before replacing MAF (this was done just a month or two ago by a Porsche mechanic).

I'm almost 100% convinced this is a DMF issue. I know the DMF hasn't been changed for at least 50k+ miles. If anyone has other ideas, I'm all ears to hear what you have. It's a major PITA to replace the DMF so I want to run through the easier fixes first.

dmboxster · 03-26-2019, 09:43 AM

Another follow up,

Checked the LTFT values today after some freeway driving. Looking at +15.6% and +14.7%. I either have a vacuum leak somewhere (intake boots?) or the MAF is done. Ordered a smoke machine off Amazon, I’ll update after the smoke test.

In other news, I test drove a 2012 Panamera yesterday. It actually shakes more at idle than my current situation. So maybe I’m in the clear on the vibrations. Another thing I noticed is that the vibrations are about 2-3x as bad with the A/C compressor engaged. Without it, it’s far less noticeable.

dmboxster · 03-29-2019, 08:58 AM

Broke down and ordered a new Mass Airflow Sensor. Replaced it this morning. Vibrations again are slightly less, somewhat back to what I remember as normal. In a happy note I do see that the trim values are now coming down. They went even more negative after this screen capture was taken. Hopefully it'll bring the long term back around 1-2%.
Screen Capture of LTFT and STFT

Final step will still be to run a smoke test on the system to make sure nothing is leaking. I have a slight feeling it could be the throttle body gasket.

dmboxster · 07-11-2019, 12:14 PM

Just to follow up this thread with the root cause of the issue.

Turns out all the vibrations were from the DMF failing. Tore down the transmission and replaced it. All vibrations are now gone. Still having some issues with high trim values but will follow that up separately.

kenkros · 09-30-2019, 06:35 PM

I'm experiencing identical symptoms, but haven't noticed any noises or clutch issues that are normally associated with DMF failures, so I'm curious to know what was the failure mode of your DMF?
Thnx

dmboxster · 09-30-2019, 06:57 PM

Quote:

Originally Posted by kenkros

I'm experiencing identical symptoms, but haven't noticed any noises or clutch issues that are normally associated with DMF failures, so I'm curious to know what was the failure mode of your DMF?
Thnx

In my case the car still shifted great, drove well, had all the power same as usual. Just had some vibrations at certain RPMs ~3k was the worst. They suddenly went from barely noticeable to bad. I tried everything else trying to fix it, but it was the DMF. Once I got the DMF out I tried to see what was wrong with it. It would spin about 3 degrees in either direction and then stop, but wouldn’t return back to center at all. After replacing it the vibes went away. If the engine is shaking the whole car then you’re probably experiencing the same thing.

BYprodriver · 10-01-2019, 08:16 AM

Quote:

Originally Posted by dmboxster

I'll give replacing the all the plugs and the coils. The car's got 90k on it and I doubt the coils have ever been replaced. If this doesn't work then I'll try the DMF.

If a coil is not performing right you will get a misfire code for that cylinder. My 2000 S has it's original coils.