lbk8950

I have read the rough idle threads...and none of them are quite on point. I have the (apparently) trademark vibration in the seat at idle. It is better when I turn the AC off and even better when the climate control is off. I have a 2005 C2 with 39k miles. Oil was changed regularly and no metal shavings, bits, etc. in the filter at the last oil change.

I just changed plugs and coils and the vibration is still present. I plan on cleaning the MAF this weekend. I have no codes. The car otherwise runs well. The vibration smooths out at 1k rpms. If the MAF cleaning doesn't help, my next thought was engine mounts. Any other suggestions?

BHMav8r

Mine too. No codes, changed plugs, still rough. No help from the stealership.
Keep us posted . . .

neanicu

Vacuum leaks. They manifest most at idle and when engine cold.
Check for that.

slicky rick

Im going to watch where this one goes....

GraSox

Same issue here....we've got to figure this out!

Spoddle

Same issue here as well with my 05'. I've also experienced random misfire codes.

Edgy01

When were the plugs and coils replaced? What part of the country are you in?

Spoddle

I replaced mine roughly 8k miles ago, and I'm in N. VA.

lbk8950

I'm in Michigan. I replaced the coils and plugs about 500 miles ago. No improvement.

Macster

No codes? No pending codes?

Maybe the idle roughness is normal? These engine are smooth but idle is a bit rough. VarioCam Plus kicks in and reduces lift to lower pumping losses and improve emissions. As a result the engine doesn't idle quite as smooth as it might otherwise.

FWIW, I sometimes get a bit of rattle from my '03 Turbo's passenger seat due a idle vibration. Nothing gruesome. There doesn't seem to be any pattern to it. I run the same gasoline (Shell V-Power 91 octane) each fill up and the car gets used regularly.

The Turbo has VarioCam Plus while the '02 Boxster does not. The Boxster engine idles smooth as a sewing machine.

How about a 40 or more mile drive? Take off down the freeway and at 20 miles or so turn around and drive back. Avoid traffic you want the engine to run at a steady RPM for some time. No need to get crazy with the car either just set the cruise control at the speed limit and sit back and let the engine run .

After one of these drives engines in my cars are smoother and more responsive.

If you want run a bottle or two of Techron through the fuel tank. Follow the instructions on the label. I like to change the oil/filter shortly after using Techron.

Dadio

Have you cleaned the intake plenum ?

TIMBERHOLLOW9310

This sounds like my C2 06 (12k). Just a bit rough at cold idle, nothing huge...smooths out after warm up and spirited drive.

lbk8950

I have not cleaned the plenum, I can try that as well. It does not really improve after long drives, etc. It is certainly worse when cold. This could be no problem at all. It is just that I never experienced anything like this in my 06 Cayman S.

RaidersR1

+1. I had the same issue...but it was not all the time....cleaned the plenum and haven't had the problem since.

Macster

Worse when cold suggests an engine being incorrectly fueled for the temperature. This can arise from a bad (they can be intermittently bad) coolant temp sensor or an intake air temperature sensor. The air intake temperature is a function of the MAF (in those engines that still have a MAF).

You might be able to spot this with an OBD2 code reader/data viewer by observing the intake and coolant temperatures at engine start and while the engine is warning up. You are looking for a temperature reading that disagrees with ambient at engine start. One that is higher than ambient and markedly so.

In some cases the temperatures will not be at ambient. It can take quite a while for a car and its engine coolant and oil to reach ambient temperature. It requires the car be in a stable temperature for some time.

Once you start the engine the coolant temperature should rise one to two degrees F every second or so as the engine idles and warms up. At least this is the case for both of my cars. Intake air temperature can climb a bit as the engine compartment gets warmer but it's rise will not be nearly as dramatic.