jb26jb

Is it missing at idle? Is it just vibrating. On a '99 it could be your ICV idle control valve, plugs, coils, bad tank of gas, dirty injectors etc. Run some techron throughout see if it helps. I would not be surprised if it was cracked coils.

gregroselli

Could you define "missing at idle" and "cracked coils" so I have a better idea what we're talking about? thanks

99firehawk

cracked coils on a 996? not likely
does it get worse with the ac on ?

Jake Ok

No missing idle just vibration in passenger seat. Is it NORMAL ???

gregroselli

I've seen a lot of threads about the passenger seat vibration and everybody seems to write it off as normal. I'm getting it in the driver seat (although the passengers can feel it too) and it's way too significant to be normal for any car.

jb26jb

There are seperate coil packs for each cylinder they are known to split and crack leading to a rough idle and a slight misfire noticeable at idle eventually getting worse causing a CEL and more pronounced misfire.

Happened on mine and other people on the forum. Do a search. I would try the techron with the next tank and see if that helps. Just my .02 take it for what its worth.

Benjamin Choi

my sport seats shake

Nicolaasdb

mine 99 vibrates as well....when I put it in neutral it gets less....I think it started when I changed my exhaust from original to sport.....but I might be mistaken.

Can this vibration realy be caused by a weak battery??

GNR996

For what it's worth, mine always has. An 03' with 28,000km when I picked it up.

Thinking it was normal being a performance car and all. Friend got in the car one day, had never been in a P-car before, thought "wow, this thing has attitude!"

As far as gas goes, maybe I'm nuts or just wishful thinking and not that it matters, but I'm sure I am getting better mileage out of the higher octane gas, maybe another liter/ liter and a half every 100k. Gas stations here only have 91 octane except Chevron they have 94. Sure the switch has helped some.

Plus since I asked about the yellow goo in the oil filler neck I have been as suggested "driving it like I stole it". Thanks Tim.

Still loving my p-car, stupid fast, good looking, comfy and entirely practical for a daily driver.

Tippy

My car is tiptronic so there is a constant load on the engine at a light. I chalk it up to being a small 4-valve motor, meaning, it doesnt make a lot of low end torque so if a load is placed on it, you will feel all the firing pulses causing the vibrations.

99 C4

I get the vibrations only when the AC is off. I went to the dealer to get this looked at 3 times. It turns out that I was shutting off the AC. Apparently the system was designed to have the AC on at all times. Now I keep the AC on and no more vibrations. Yes I leave it on in the winter too as it helps with the humidity. The compressor turns itself off when the temperature drops below a certain point. When I have the windows down I turn off the air completely.

ZX9RCAM

I had the cracked coil problem as well.....was only noticeable at high rpm's, then
I would get a flashing CEL & the code reader told me what it was.

911fiend

Last night I was doing 100+ and trying to max out when the CEL started flashing, I looked behind me and there was an enormous cloud of dark smoke towering 20 ft into the air. I've seen the black smoke before but never that much. After a little while the CEL stopped flashing. Everything seemed normal, no noises or weird behavior. I called the dealer and he said even though the CEL was flashing I don't need to bring it in. The CEL probably got tripped because of all the black smoke but since it stopped the car is fine now. I guess the severity of the cause for a flashing CEL varies...

cdodkin

That's not normal.

I'd be having my car looked at if it did that.

Benjamin Choi

lol