Violent vibration and STFT swinging

[cx1eb.w]

Year/Make/Model: 2005 Mazdaspeed Atenza (MPS)
Mileage: 180,000 km
Location: New Zealand

Primary Concerns:
1. Severe vibration when coming to a stop and occasionally while driving.
2. Idle hunting / fluctuating STFT causing jerking under load.

DTCs:
None

ECU/Tuning Software:
Cobb Accessport (Stage 0)

Tuner:
Stage 0 OTS

Was the issue present before tuning?
Yes

Is the concern intermittent?
Yes and No. STFT swings +20 and -20 all though out the car running and jerking happens all the time felt though 1-3 gear. The vibrations are sometimes while driving but all the time when coming to a stop.

Can you duplicate the concern?
Yes to both.

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ISSUE #1 - VIBRATION / DRIVELINE
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The main issue is a violent vibration that occurs roughly 1 second before the vehicle comes to a complete stop. The best way I can describe it is that it feels like sitting on one of those old TV workout/vibration machines.

The vibration occurs every single time when slowing to a stop.
Its felt thoughout the entire car, not just a pedal

According to the workshop, it can also happen:
- During deceleration.
- Occasionally while cruising.
- Sometimes while taking a slight turn.

I have not personally driven the car much because it has spent a lot of time in workshops since I purchased it, but those are the symptoms reported to me.

The issue seemed to appear quite suddenly. Once it became noticeable when stopping, I took it straight to a workshop because I did not want to risk causing further damage.

Workshop findings so far:
- Rotated tyres.
- Checked driveline.
- Checked wheel bearings.
- Checked U-joints.
- Replaced rear diff bushes (they were completely worn out).

No obvious fault has been found.

Interesting observation from the workshop:
If the handbrake is engaged by one click (just enough to illuminate the brake warning light), the vibration disappears completely, including when coming to a stop.

They have suggested the issue may be related to the AWD system because the symptom only seems to occur when the car is operating in AWD. They mentioned they were going to unplug a component related to AWD operation and road test it, but I have not received an update yet. But doing that only comfirms its a AWD related issue and not what to fix haha.

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ISSUE #2 - IDLE HUNTING / STFT SWINGS
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The second issue is unrelated to the vibration and its been a thing since owning the car, but I am including it in the same post since some members may have seen similar symptoms.

The car hunts at idle with a noticeable fluctuation in RPM. It is audible and visible, although not extreme. The RPM change is approximately 200-400 RPM.

Symptoms:
- Occurs cold and hot.
- Audible idle hunting.
- STFT constantly swings between approximately +20 and -20.
- LTFT remains fixed at (iirc +)0.16 and never appears to move or adjust.

Under load, the vehicle can jerk during acceleration, almost like someone learning to drive a manual and slipping the clutch. The sensation becomes less noticeable through the gears and is mostly gone by 3rd to 4th gear.

Work completed relating to this issue:
- Smoke tested intake system.
- Smoke tested exhaust side.
- Turbo system checked.
- No leaks found.
- MAF checked and cleaned.
- New iridium spark plugs installed.
- PCV hose S-bend pipe and (I believe) the valve were also replaced due to being accidentally broken during work and were replaced.

A faulty throttle body was found early on. The original throttle body would only open to roughly 70% and would "glitch out" during its self check. It has since been replaced with a used replacement and that particular issue has been resolved.

One interesting thing the workshop noted was that when they unplugged the up stream / front O2 sensor, the engine apparently ran normally (no jerking iirc also). I do not fully understand why, but this is what they reported.

The workshop currently suspects an O2 sensor issue. This problem existed before installing the Accessport and appears to be gradually getting worse.

If replacing the O2 sensor resolves it, I will update this thread. In the meantime, I am open to any other suggestions.

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REPAIRS COMPLETED WITHIN THE LAST 3 MONTHS
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- Timing chain.
- VVT actuator.
- Timing chain guides.
- Timing chain tensioners.
- Water pump.
- Clutch master cylinder.
- Clutch slave cylinder.
- Engine mounts.
- CorkSport HPFP internals and O-ring rebuild kit.
- Cobb Accessport (Stage 0).
- Replacement throttle body.
- New battery.
- Door lock actuator.
- New windscreen.

VCTS also gave out during me learning how to drive manual for the first time and caused engine light, but was replaced and has not been issue since (stft issue was a thing before this)

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MODIFICATIONS
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Installed before I purchased the car:

- BC Racing Gold coilovers.
- HKS Super Suction intake.
- Filter was replaced shortly after purchase as the old one was falling apart.
- RX-8 rims.
- GFB BOV.
- Front strut brace.
- Rear strut brace.
- Aftermarket boost gauge (currently reads incorrectly).
- Cheap Chinese Windows CE head unit.
- Mufflers removed

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ADDITIONAL NOTES
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There may be details I have forgotten. If anyone suggests something that has already been checked or replaced, I will let you know.

At this stage I am mainly looking for ideas regarding:
1. The severe vibration when stopping, especially given the AWD related observations.
2. The hunting idle, STFT swings, and jerking under load. (also note clutch is fine)

I'll post driving logs (when i can) from when I had the car as I was able to get some when I had the Accessport plugged in.

Any suggestions are appreciated.


Edit: datalogs attached, nothing different happened to the car on either, one was just a longer drive then the other.


Edit 2:
STFT swing / jerking while driving issue fixed!!!

Upstream O2 sensor was alive enough to be giving readings, but the readings it was giving were extremely wrong.
Replaced upstream O2 sensor and it drives amazingly.

I'm still unsure about the vibration issue, I think its the diff, but I'm open to other things to check before I get onto that.

 

[cx1eb.w]

Another note I just remembered:
The vibration also occurs when rolling to a stop without applying the brakes.
Putting the car in neutral, or simply holding the clutch in while coming to a stop, does not prevent it. The vibration still occurs with zero brake input.

 

[Raider]

Another note I just remembered:
The vibration also occurs when rolling to a stop without applying the brakes.
Putting the car in neutral, or simply holding the clutch in while coming to a stop, does not prevent it. The vibration still occurs with zero brake input.

Perhaps there is a loose motor mount.

 

[Enki]

I'm wondering if you mightn't have some issue with your ball joints up front.
Also, what are the specs on your wheels? Perhaps the scrub has changed to be closer to zero, allowing the wheel to oscillate back and forth a bit in certain circumstances.

 

[cx1eb.w]

Perhaps there is a loose motor mount.

I had all of them replaced since the top one on the master cylinder side had busted open. Found out about 2 weeks into owning the car :')

I'm wondering if you mightn't have some issue with your ball joints up front.
Also, what are the specs on your wheels? Perhaps the scrub has changed to be closer to zero, allowing the wheel to oscillate back and forth a bit in certain circumstances.

I believe the shop checked the ball joints. They checked rotors, break pads, I think the control arm ad a whole tbh.


Need to note though, it entirely goes away with 1 click on the handbrake, so with that info, I'm assuming its something to do with something in the AWD. I'm personally thinking its the rare diff, I'm getting someone who knows more to take a look at that at some point next week. But if not that, maybe even the clutch coupling unit mounted at the rear differential? Then the axels are also on the list but iirc, the garage has already checked those.

I'll edit this comment with wheel specs once I get a chance, they are on RX8 rims however. On bcracing coilovers also.

 

[Enki]

I think it's the PTO that disconnects when signaled, not the rear diff. I could be wrong though.

 

[cx1eb.w]

I think it's the PTO that disconnects when signaled, not the rear diff. I could be wrong though.

Only reason I say its the rare diff is because, with no power going to it, it's loose and just spins free, so no vibration. But once you're on the throttle, it loads up and locks/tightens, and if there's wear in there, that's when it shows up as vibration. I'm only trying to think of things that would "engage" while the car is in AWD.

Fact check me on that though, I honestly have no idea...

 

[Enki]

Question is, does the drive shaft spin with the rear wheels when "disconnected" or does it not move while the rear wheels do? This should tell you where the "disconnect" is taking place.

 

[Easter Bunny]

There is an electronic clutch at the front and back to disconnect the driveshaft for fuel efficiency

 

[Enki]

One at each side of the driveshaft? That's a bit odd, but I guess it makes sense, as it would be removing that mass from energy requirements for rolling.

 

[SyntheticAtmosphere]

Speed6 has a electronic rear diff. drive shaft spins via the PTO all the time. PTO is fed from the trans at the right front CV shaft output.

 

[Cold Lotion]

Lots of misconceptions about how the AWD system functions. Any metal member can look at the technical training document https://www.mazdaspeeds.org/threads/2006-ms6-tech-training.10863/

If the vibration totally goes away with the handbrake engaged, I'd be looking at the rear differential. Not only can the bushings wear out and fail, but the case itself can break.

 

[cx1eb.w]

Hehehehe, got to checking the diff, shes f***ked.
On the magnetic drain plug came out some quite big chunks. If I remember I'll try upload some photos I got.

I found a diff and axels for a good price, will probably get both done while that areas been worked on.

Note: Have not driven the car yet, so I don't know if that's what's caused the vibration, but is highly likely. Just wanted to post findings on here for now. Will be replacing the diff now.

Another note: Looks life the diff oils NEVER been changed, probably still the factory oil HAHA