[luis77]

Hi,



I am experiencing awful engine vibration (as if motor mounts were bad) (not shaking) only at idle. If I operate the power windows when they are already up, idle drops a bit and the vibration worsens. I have a brand new battery. Alternator reads 13.4 volts. No lights dimming or anything. Balance shaft rechecked. Do you think a faulty alternator may be lugging the engine making it vibrate?

I am not sure if the <acronym title='dual mass flywheel'>DMF</acronym> is expiring. Car does not vibrate at all above 1100 rpm all the way to red line. Don't know whether it is the alternator or the <acronym title='dual mass flywheel'>DMF</acronym>. Also headlights vibrate on idle and vibration worsens when aux fans kick in at high speed or when compressor engages vibrations worsens for a couple of seconds before idle stabilizes. Motor mounts were recently replaced and are OK.



Any suggestions?

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[unknown4u]

Do al the cilinders work correct? Enough fuel and spark? The engine is 100%? No bad cilinders or so?

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[Rob in Oz]

Is your balance belt intact? Mine wasn't - it was curled up in the bottom of the timing case...

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[flash]

check to see if the air conditioning compressor ear or ears are broken. it is very common. people are known to adjust their belt without loosening the mounting bolts first, and it breaks the ear.

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[Ryan]

Is the car a Tip or 6 speed?

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[Cloud9...68]

Replacing the motor mounts involves removing an awful lot of stuff. Have you gone back and checked to make sure all nuts and bolts are properly tightened, including things like the crossmember mounting bolts?

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[luis77]

My Car is a 6 speed

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[flash]

seriously, i'm betting on the AC compressor ears

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[luis77]

My compressor is brand new and was replaced correctly using the proper procedure.

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[flash]

hmmm - well, i always suspect new parts long before i suspect old ones.

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[luis77]

I don't want to spend 1k on a <acronym title='dual mass flywheel'>DMF</acronym> without knowing the exact symptoms. Someone posted that vibrating headlamps and idle vibration that goes away at 1100 RPM's and above indicate an expiring <acronym title='dual mass flywheel'>DMF</acronym>.



Any comments?

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[flash]

unfortunately there is no real way to determine if the DMF is the problem, without tearing things apart to test it, and even then the test is so primitive that you might not get your answer.



i've seen idle vibrations due to worn distributor contacts, worn out spark plug wires, or even loose spark plugs.



the biggest mistake is to assume that something that was just replaced is not the problem. very often it is exactly the opposite.



you're going to need to go through all of the little things, ASSUME NOTHING, and eliminate those one by one. hopefully you will turn up the culprit, and it not turn out to be the DMF.

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[Cloud9...68]

The symptoms sound a lot like mine before I replaced my motor mounts, the rubber on one of which was split. That's why I would start by checking all the fasteners that had to be removed to replace the mounts, primarily the crossmember to chassis, and motor mounts to crossmember. Another member here recently found one of his crossmemebr bolts to be missing altogether. At least it's free. But of course, like Flash says, it could be any one of a dozen other things. Does the blink test reveal anything?

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[luis77]

What about when I operate the power windows for example and the window is already up and the car vibrates pretty bad and idle drops. Is this normal on 968's? Or I may have an alternator issue?

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[flash]

i think you're over-thinking that. the idle drops because there is an increased load on the engine when you hit the window switch.



i would look at your idle control valve, and the ignition system.



occam's razor

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[Cloud9...68]

Also, when the window is partially lowered, it will naturally rattle more if there's a vibration somewhere, which will accentuate the perception of the vibration. Idle control valve and ignition system are good places to look. Take a look at the distributor mounts, which are the black magnesium pieces where the distributor connects to the head. Those have been known to sometimes corrode, which can lead to an unstable idle. Start by taking the cap off and taking a close look at the contacts, and at the rotor, for signs of wear, particularly uneven wear. But whatever you do, thoroughly check all the components on your car that could be related to the problem before you start spending money throwing parts at it. Good luck - problems like this can be tedious, time-consuming, and frustrating.

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[tamathumper]

It is *not* normal for the car to vibrate when you roll the windows up - nor when you perform any other normal electrical function like turning on the AC or the vent fans.

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[flash]

no, it is not normal. i was only saying the current draw would increase the load on the engine, making the symptom of the larger problem appear.

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[DaveN]

I would still question the alternator. Windows and such draw a lot of current. This comes from the battery until the regulator says it's time to top up the battery with the alternator. Is there a smal delay before the rumble starts when rolling down the window? If so I might suspect the alternator is binding under load. Remove the alternator belt and see if your problem aleviates.

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[tamathumper]

@flash, yeah wasn't disagreeing, just clarifying in case the point was left hanging out there.

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