VIBRATION AT IDLE

when my car is at idle i can see passenger seat vibrating. only had the car a month , its a 99 C4 is this normal?. I have checked the seat its not loose, there is a very slight fluctuation in revs but nothing major its done 33K.

My '99 C4 did exactly the same. Seems the seats resonate quite happily at the same frequency as the engine ticks over! Harmless but annoying and likely not indicative of a problem. If you feel all is not well, then have your OPC / Specialist check a few things that can cause uneven idle: 1) Vacuum leaks - Split oil return bellows. Split oil filler pipe, damaged / corroded seal on oil filler cap. Loose vacuum pipes anywhere on the engine. RMS or cam cover seals (where oil can get out, air can get in). Damaged oil separator. 2) Mechanical - failed variocam unit(s). Absolute cam phasing (the position of the cams in relation to the crank, governed by the cam chains and set during engine assembly. Cam chains aren't averse to jumping a tooth as the cam tensioners and pulleys wear). Compressions (the dreaded Locasil disintegration - shows as low compression on an affected cylinder). Failed hydraulic tappet(s) - loud click-click at tickover. Faulty spark plugs / coils / fuel injectors / fuel filter / pressure regulator. 3) Sensors - Lambda (O2 - oxygen) sensors in the exhaust - these totally control the tickover mixture correction and have a finite life - likely to be dead by 60K miles if not sooner. MAF sensor - gradually falls out of calibration with age / miles - will also cause rough running at large throttle openings and higher rpms. Variocam sensors - stop the variocams changing the cam phasing. Temperature sensors - keep the ECU on cold programming, cause over rich / over lean mixtures. Most of these would be picked up by the PST-II tester but some (MAF and small vacuum leaks particularly) will need someone who knows what they're doing. Hope this helps Ian W

You will see a thread on the 997 board about rattles and stuff, and it appears that the 997 suffers from the vibrating passenger seat. My 996 never did. I do agree with Ian, if you bought from an OPC bother the hell out of them until you are happy

Mine does it too - annoyed me for about a nanosecond then moved on

Thanks to all for advice. Going to get it checked at opc will post any info if it turns out to be sinister

.....or it could be some pesky £ound coins that had fallen down the side of the seat that were rattling. [ ] Good day for me that was when the valet man informed me.

Ever since I fitted my Fabspeed, my passenger seat vibrates with the resonance of the low rumble of the exhaust at idle. If you have a sport exhaust this could be the reason.

My passenger seat vibrates as well. The tickover is the at the resonant frequency. There's not much you can do to stop it. In my case it also started rattling, which got worse over time. However, one day I got sufficiently irritated by it, that I moved the angle of the backrest and this stopped the rattling. Also I have had a couple of passengers in the car and at the moment it seems not to be vibrating as much or making any noise. I guess moving it slightly may have changed the frequency or something.