hi! Can anyone help me please. My 996 Mk2 facelift 2002 MY when radiator fans starts working especially in high Revs but in the idle too the car it has vibration. Or the same think exists when the Air con. it turns on. I have changed all coils new and the engine mounts are okay. Anyone has the same experience to help? thanks!!!

 

My 2002 Boxster sometimes manifests a bit of a vibration -- not the best word to describe what I feel/experience but it will have to do until I think of a better one -- when the radiator fans kick on or I turn on the A/C.

Not a vibration but more a sign the engine is working a bit harder than usual. This is in some ways "normal" as with the radiator fans turning on or the A/C being switched on represents an increase in electrical load which means the alternator has to work harder to supply the electrial power to the radiator fans or to the A/C compressor's electro-magnetic clutch. The cabin vent fan is also an extra electrical load. Additionally besides any additional electrical load the A/C compressor represents an increase in engine load to spin the compressor. To get the alternator to produce more electricity at idle requires more electrical power be fed to the rotor. All of this means the engine has to work harder to supply this extra load but with no increase in RPMs.

This behavior is normal (unless it is not and that depends upon how severe the behavior is) and is noticeable at least in the case of my Boxster because the engine is so smooth running at all other times.

Now with my 996 Turbo the engine is not as smooth running as the Boxster engine. Under the same conditions there can be some vibration of a very mild sort but it can have some interior areas making some noise. Nothing scary or even bothersome and at engine speed above idle the vibration is gone and after a while -- the engine warms up and the battery gets replenished -- even at idle the vibration is gone.

Assuming the symptoms are not that bad in the case of your car all I can suggest is ensuring the engine is in good tune. Various things can affect the engine tune.

First do an E-Gas calibration. The steps should be documented in your car's owner manual but from my memory: Start with the key off and your foot off the gas pedal. Keep your foot off the gas pedal through the procedure. Turn the key to the on position and leave on for at least 60 seconds. (I use the in-dash digital "clock" to time the 60 seconds (one minute).) After at least 60 seconds have elapsed turn the key off for at least 10 seconds. The next time the engine is started the calibration is complete.

Be sure the engine air filter is not too dirty. I let my Boxster's air filter go I don't know how long and then when I went to change the filter found the top of the filter covered with leaf trash. (Don't forget the cabin air filter too. It can collect considerable dirt/trash.)

After I got the old engine air filter out of the car and was able to remove the foam covering and then turn the filter upside down and smack it against the sidewalk the amount of black dust (mostly tire rubber dust I suspect) that came out of the filter folds was amazing. Afterwards with the new engine air filter the engine ran better. The filter was that dirty.

My Boxster engine perked up some after I switched from running Shell V-Power to Chevron Supreme. The Techron in the Chevron gasoline was the difference.

You can switch to Chevron gas for a tank or two or run a bottle (or two) of Techron through the gas tank. When I do this the bottle I buy treats 20 gallons of gas but I just dump the entire bottle into the gas tank (which holds 16.9 gallons (Boxster) or 16.6 gallons (Turbo)) then fill up the tank with gasoline.

The general rule is if you notice any improvement to repeat the treatment with a 2nd tank of gas after the 1st tank of gas is down to the point you need to refill the gas tank. My advice is as long as the engine is not running any worse to repeat the treatment.

It is also advisable to change the engine oil and filter after using Techron as it increases oil contamination.

I can tell you that when I had the O2 sensors replaced in my Turbo at 132K miles and prompted by an O2 sensor related CEL (P0135 was I think the error code) the engine ran better afterwards. It was not running bad before but there was a noticeable improvement with new (all 4) sensors installed.

Later with my Boxster I replaced all 4 O2 sensors at around 305K miles -- prompted by I think a CEL but I don't recall the error code now -- but I don't recall any change in the engine's behavior.

With the Turbo then at something over 140K miles I replaced the coils -- they were original -- and the plugs which had around another 10K miles to go before they were replaced -- and the engine ran noticeably better than before.

The replacement of the coils was prompted by occasionally the Turbo would misfire right after a cold start if I let the engine idle some time but it would never misfire at any other time. Neither the tech or I believed the coils were to blame but I replaced the coils just to be sure. (The misfires are probably due to one or more lazy injectors but the injectors do not warrant replacement. I avoid the misfires by not letting the cold engine idle for any length of time after a cold engine start.)

As for the plugs I had replaced the plugs several times before -- on miles -- and the Turbo engine never reacted one way or the other so I attribute the engine perking up to the new coils.

The coils in my Boxster are original but the next time I have it for new plugs I'll have the coils replaced just to satisfy my curiosity as to what effect (if any) new coils willl have. The coils have been in service now for just over 315K miles.

At some point in all the above -- new O2 sensors, new coils (and plugs) -- the Turbo lost its "tranny rattle" which would occur when the engine/drivetrain were fully up to operating temperature and I'd roll up to a stop concurrent with shifting the transmission into neutral and releasing the clutch pedal. I'd hear some "rattle" as the engine idled and I waited for the light to change. When I first heard this I suspected it was from the transmission and pushed the clutch pedal down and the noise went away. The noise did not return upon releasing the pedal unless I revved the engine a bit then let it return to idle.

I mention all of the above to reinforce how important it is to ensure the engine is in proper "tune".

It is so easy with modern cars and their sensors and what have you coupled with the long plug life, coil left, no ignition points to set or replace, etc., to forget that at least in some cases even if there are no errors or even any real symptoms -- I thought the Turbo transmission rattle "normal" as I have heard transmission rattle from other cars I have owned -- the engine can benefit from periodic replacement of these items, besides plugs which have a service life, but also O2 sensors and coils.

As these sensors or other items degrade while the engine may not manifest any CEL or even any real signs of any trouble the sensor or item degradation can affect the engine.

Hence the vibration you feel may just be the engine's way of telling you it needs Techron, a new air filter, or possibly even new O2 sensors, if you are so inclined to replace sensors on nothing more than some hope it may help.

 

Dear Macster ,

I am thanking you very very much for your detail explanation and for your help!!!!

I will.do all.these you deacribed!!

Best Regards
Marios