When driven in heavy rain, my '03 EvoVIII has enhanced engine vibration at idle.

It feels as if some sort of insulation or motor mount starts transmitting more vibration than when dry. At a stop at idle, the engine vibration seems to be transmitted more. Giving throttle provides more vibration and sound than normal, but smooths as the rpms rise. Driving further in less wet conditions, it goes away, and is not there under dry conditions.

The car is idling at its usual lumpiness at normal rpm. Standing outside the car it does not sound differerent. It revs, pulls, and stops normally.

Exam at dealer found no exhaust out of whack or abnormal sounds (dry, of course).

The car: 2003 EvoVIII. Turbo-back signature exhaust from Vishnu. Rear Cusco swaybar, stainless brakelines, front Racingbrake two piece and pads. Vishnu adjustable cam gears, XEDE with Shiv tuning. Perrin shortie antennae (hey, you never know).

OK, Sherlocks, what is it? I have no clue.
Doug in Cincinnati

 

I assume you have the stock air box with Vishnu... MAF problem.

 

Yes, stock airbox and filter.
But, even at idle, the idle itself isn't altered, just the vibration.
Doug in Cincinnati

 

Maybe a grounding issue? IDK? Have you tried a ground wire kit?

 

If you are running the A/C, lights, wipers etc you might need to check the condition of the serpentine belt as it may not be driving all the ancilliaries effectively when it gets wet...
Have you had your timing belt changed recently?

 

if you have your air setting to "defrost" ... and have your fan turned on.... your A/C compressor runs even though the ac light/button is not on..... its your A/C

 

Just trying to keep up with the ideas, here...

4bngr: Why would a bad ground generate this syndrome?

Andrew: If the car continues running in drier conditions, the syndrome reverses even without altering the AC/fan settings. Does that work with your belt idea?

akEvo: Ditto?

Doug in Cincinnati

 

I would look at the coils and wires.

 

Try cleaning the MAF, since it's the first sensor that would be directly affected to weather changes.

 

Barry (Andrew's Dad) weighing in with more speculation. If the ancilliaries belt were heavily loaded and wet, as suggested, it could skip and vibrate if loose.

Another question, is this perhaps an airborne vibration or evident as a mechanical vibration as well? At low speeds the air flow from the A/C fan and blower fan can beat with the frequency of the engine to produce what feels like a vibration but is actually only airborne resonance noise. Additional test: Is it still apparent when hands are placed over the ears? (Carefully positions concealed camera to catch Doug trying this out for later posting).

 

Daddy Punchard has the FUNNY!!!!

 

I think awhile back someone found that an aftermarket exhaust when realy wet flexed and was hitting the drive shaft. Maybe?

 

my 03 viii did this stock and still does it when raining. i thought it was an evo characteristic.

 

Update,

For mmoranda: The Vishnu catback signature had a problem with the counterweight on the drivetrain that caused a horrible clacking sound and was only evident when weight shifted in the wet. Andrew at Dynoformance diagnosed that one for me. But the turboback doesn't do that.

For asasin79: No that's not a basic Evo characteristic and for me it comes and goes with heavy rain/water on the road.

For Andrew: Sorry? Can't hear you? Oh, yes, I'll try it in the car next time. Last time I had to do that it was around NOIZE at Dyno4mance.

We had some rain this morning and I got just a little of the vibration, but not prolonged enough to try the A/C compressor, etc. issues. I plan to take her in for an oil change and share these diagnostic suggestions, including checking out the exhaust and engine mounts.

More ideas welcome!!!

Doug in Cincinnati

 

You may not like the idea, but I vote for it being an evo characteristic. My '03 does the same thing. That doesn't mean it doesn't have a cause, just that it's normal for an evo to do this. With that being said though, I hope you find the fix so that I can do the same on my VIII.