Engine Noise/Rough Idle

[ijbrekke]

Alright, I need help diagnosing this. I have a few noises that are bothering me, and I don't know how related they are to each other:

-The engine has slowly developed a very shaky idle. It's not jumpy at all (very steady), just shakes the entire car.
-It has also developed a strong low resonance, like bass on a stereo that is turned up loud. This pulses with the engine, and is very noticeable below about 1500-1700rpm.
-When it is cold out, the engine seems to "whistle", especially at startup.


I cleaned the EGR valve, which made zero difference. Yesterday I also checked my air intake hose, saw some hairline cracks, and put duct tape around the tubing. This made the shaky idle somewhat better, so tomorrow I'll go buy a new hose from the dealer. But it made no difference with the bass resonance or the whistle at startup.

I had all 4 motor mounts inspected, and had the front replaced along with the addition of RR Racing inserts. I should add that the bass resonance and shaky idle were happening before I did this, and this simply changed the dynamics of the problem, so I don't believe the mounts are the source.

I've done spark plugs recently, but not wires. The car is also running with an MP3 ECU.

These are all the details I can think of. The problems are not native to the car because they didn't exist when I bought it a year and a half ago.

Thank you in advance for your help! Any thoughts?

 

[ijbrekke]

Going to get that air intake hose now, we'll see if it makes a difference.

 

[ijbrekke]

Got the new hose on, and it's slightly better, but still intermittently shaking. It literally feels like the engine is connected directly to the chassis or something. I climbed under the car to check exhaust alignment, etc. and everything looked normal, with very little movement. I just can't figure out what would be causing this. Plug wires? Vacuum leak? Coil packs?

Need ideas.

 

[turdb0]

I had exactly the same problem. The engine idles really rough and it feels like I have some really stiff motor mounts because the car shakes and makes the hood rattle.

 

[ijbrekke]

Updating an old thread because I finally fixed the problem:

After trying everything listed above, I finally took the car to a transmission shop because I had suspicions about the clutch. My theory was that because the car ran fine but had a "wobble" consistent with engine rpm the problem must be a rotating physical part attached to the running engine (I thought it might be a cracked flywheel).

The problem turned out to be a botched clutch install from the previous owner. The clutch was not a Mazda part, and the installer didn't resurface the flywheel but instead "roughed it up" with sandpaper. This gave the clutch a nice, powerful grab at the beginning of its life, but over time chewed up the friction plate on the clutch. The engine shake was coming from the pieces of friction plate that had become embedded in the flywheel AND from the loose pieces flying around in the housing that had been eaten off the clutch.

So after a long hunt, I finally found the problem. Needless to say the car is back to normal, and the new clutch has also immensely improved shift feel and positive engagement. Hope this helps someone down the line!