dkem7

I just changed the plugs over the weekend (99 996) and added Techron to the latest tank of Walmart gas (only 93 in the area - 10% Ethanol). I am now experiencing a pronounced engine vibration that starts at a little under 2000RPM and extends up through the rev range. It is similar to the vibration many describe as occurring at 2K but does not go away with more RPM. It can be felt in the floor while driving. The vibration is worse the hotter the cars gets - water over 180F.

The same vibration is present additionally at idle if I turn on the A/C (like a resonance in the back half of the car)? The car only had a slight vibration at idle previously and was smooth through the rev range......but, the roughness with the A/C on at idle was present.

I read a post by another member describing engine vibration resultant from a bad coil and believe this may be the closest similar issue. I am suspecting ignition at this point (coils?). The engine seems to have lost the "turbine smoothness". No CEL - closest dealer is 3 hours. Have ran Walmart gas before.

Your assistance is appreciated.

ivangene

check all the plugs and make sure they are connected to the coils, sounds like you didnt get one on right ... simple is usually right..... go where you just were and check

pszikla

Good advice!
Pete

Phil G.

Bet it has nothing to do with the Techron.

1999Porsche911

Also make sure you reconnected the correct wires to the correct coils.

auto-xr

Same thing happened to me. Replug the connectors and make sure you hear a click. The connector boots make it a little tough. I didn't drop the mufflers when I changed the plugs. If I had to do it again, I'd drop the mufflers to have better access and save time in the long run. Dropping the mufflers is only 6 screws.

Ubermensch

Agree with all of the above. It's probably a misfire caused by your installation of coils, or a bad coil. If you have a scanner avialable you identify which cylinder is misfiring and narrow down your search.

C4CRNA

Shouldn't a missfire throw a CEL?

ivangene

I agree, but wouldn't a miss fire trigger a CEL?

that's the best way to know where to look for sure! - still the solution is most likely what we said, just easy to know where to look if the reader can point to the misfiring cylinder(s)

and for goodness sake -

POST SOME PICS AND INTRODUCE YOURSELF!!!!
Where's Tim..... thats it

Ubermensch

Not necessarily. I've had an intermittant misfire that didn't throw a CELinitially. Eventually as it got worse it did thrown a CEL. Of course I'm not sure if you'll be able to pull a code prior to the CEL, but I think you would be...just not positive.

dkem7

Thank you all for the replies.

New to the board - quick into: Cedar Falls Iowa. Current car - 99 996 Black. Previous cars: 99 996 Silver & 82 911 SC - both sold in 05 due to growing family. Now, not suffering withdrawal. Day Job: John Deere (EE). Will try and get pics of the new car up.

Definitely moving wrong direction with performance. Today, I have picked up what seems to be a pronounced repeatable stumble @ 4K with somewhat flat performance and the same vibration/missing - also reconfirmed that anything over temp gauge straight up, and it starts to run worse.

I will check coil installation this weekend - I was able to check all coils are plugged in. I will verify if they are seated correctly on the plugs. Will try and dump codes if I can find a suitable reader to see pending/stored codes. No CEL. BERU plugs. Is there an easy way to verify correct harness on correct plug (even though I thought I kept a close eye on this)?

Or the MAF is spontaneously having issues (erratic output).......

Marlin

medtech

It's Definitely the Techron!