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THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHVibration at idle
Leading reported evidence
Install rennsport motormounts in my car
Performed · outcome unconfirmed
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Performed · outcome unconfirmed
The reason I say this is that I just installed the RennSport motormounts in my car and because they are considerably stiffer they TRANSMIT the cam loping of the engine more directly so the feeling is that the engine is running rougher.
Leading evidence: 'Install rennsport motormounts in my car' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Check battery and see if it's low' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Suggestion
Another possibility - You should check the battery and see if it's low.
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Suggestion · Original poster
I'll have to dig up service manual to check on the plugs/ignition, but I know the 60k miles major service hasn't been done yet so they may be a little old
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Suggestion · Original poster
I'll have to dig up service manual to check on the plugs/ignition, but I know the 60k miles major service hasn't been done yet so they may be a little old
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Performed · outcome unconfirmed
The reason I say this is that I just installed the RennSport motormounts in my car and because they are considerably stiffer they TRANSMIT the cam loping of the engine more directly so the feeling is that the engine is running rougher.
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Suggestion
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.
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Suggestion
The reason I say this is that I just installed the RennSport motormounts in my car and because they are considerably stiffer they TRANSMIT the cam loping of the engine more directly so the feeling is that the engine is running rougher.
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Just picked up a '99 cabrio and i'm getting a pretty significant vibration throughout the whole car at idle. It stops immediately once I start moving but returns when i come to a stop. Being in/out of gear and having the clutch in/out have no effect on it, so at least I can rule a few things out. Any thoughts?
I use 93 octane and the car's got 56k miles. I'll have to dig up service manual to check on the plugs/ignition, but I know the 60k miles major service hasn't been done yet so they may be a little old
You did not clearly state that it just started happening although you did state that you just picked up the car. So maybe you did not notice that it has done this all along. The reason I say this is that I just installed the RennSport motormounts in my car and because they are considerably stiffer they TRANSMIT the cam loping of the engine more directly so the feeling is that the engine is running rougher. It is not. The high performance mounts just send more feedback to the chassis. Check and see what COLOR DOT you have on the top of your motormounts and report back to the thread and I will post a followup. eric
Wish that was the case but it definitely has not been happening all along. I probably would have noticed during the test drive that the driver's seat felt like the chair in Sharper Image during idle...
I'll check the dots though and let you know. any other ideas?
Another possibility - You should check the battery and see if it's low.
If it is, then the alternator is pulling hard as it tries to run the electronics and charge the battery when at idle. This can assist in providing rough idle.
The Porsche battery maintainer solves that issue, always ensuring that your battery is topped up and ready to go.
People have noticed the passenger seat shaking (at the headrest) at idle on their 996s and mine included and have questioned it. So many on here have it that is probably normal.
Has the weather by any chance warmed up and if so could it be the A/C load?
I would change the plugs and all unless it's documented that they have been done.
I'm in New York so unfortunately the weather hasn't warmed up yet...
I'll play around with the AC/Heat, etc and see what happens. some new spark plugs couldn't hurt anyways. Any idea how much $$ a new set installed usually runs?
I don't feel much vibration in the driver seat at all. When I noticed that the passenger seat was vibrating, I thought for sure something is loose?
Strange.
Battery seems fine.
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.
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.
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.
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??
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.
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.
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.
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...
