Cayman 2.7 rev needle wiggle on idle???

[Byakkonick]

Hi everyone,

I was wondering if anyone can help me and give me some advice? I own a 2007 Cayman 2.7 and for the last month I have noticed a wiggle with my rev counter on idle. It fluctuates +/- 50 RPM's. The engine note doesn't really change though, perhaps a very very slight hunt. When I drive the car and hold the speed steady at a certain speed, eg 40 mph, I can notice the rev needle still wiggling. This is when the air con is off and on, so it isn't anything to do with that kicking in.

The oil level is spot on, so is the coolent, and the car was serviced 3 months ago by an independent Porsche dealer. The car has only covered 27 000 miles.

I am going to fill the car up with Shell Vpower fuel and add some Redex injector cleaner to see if this helps. I normally use standard unleaded fuel.

Any help would be greatly appreciated.

Nick

[rotta]

idle control valve? maf?

[Beanoir]

sounds like a dodgy cable to me especially if it's doing it at speed and not just idle...

[Rockster]

Byakkonick said:

Hi everyone,

I was wondering if anyone can help me and give me some advice? I own a 2007 Cayman 2.7 and for the last month I have noticed a wiggle with my rev counter on idle. It fluctuates +/- 50 RPM's. The engine note doesn't really change though, perhaps a very very slight hunt. When I drive the car and hold the speed steady at a certain speed, eg 40 mph, I can notice the rev needle still wiggling. This is when the air con is off and on, so it isn't anything to do with that kicking in.

The oil level is spot on, so is the coolent, and the car was serviced 3 months ago by an independent Porsche dealer. The car has only covered 27 000 miles.

I am going to fill the car up with Shell Vpower fuel and add some Redex injector cleaner to see if this helps. I normally use standard unleaded fuel.

Any help would be greatly appreciated.

Nick

If my reading comprehension is still working I gather the engine speed isn't really moving with the tach needle? A 50 +/- RPM swing would be obvious I would think but maybe not.

Assume not.

So one possible way to confirm is to get an OBD2 data viewer and view rpms in real time. The number will vary from second to second but not by much. If the variation does not match the tach display that's a tach issue (most likely). If the engine rpms are actually varying by 50 +/- that's something else.

And it is not an idle control valve as these engines do not have one. Nor can it be a cable as the E-gas uses an electrical signal from the pedal to the throttle body to cause movement of the throttle plate.

My WAG would be if the idle is indeed varying by as much as you say there's an intake air leak which points to a possible AOS but it could just be a plain old intake air leak (it happens) or perhaps the signal from the A/C compressor the compressor is engaged is faulty and the DME is constantly trying to adjust rpms for a phantom load

Most likely you'll have to have a professional take a look.

[Beanoir]

Rockster said:

Nor can it be a cable as the E-gas uses an electrical signal from the pedal to the throttle body to cause movement of the throttle plate.

Well you learn something new everyday!

[Byakkonick]

Thank you for your replies. Very informative! I think it could be something to do with the MAS because a few months ago I noticed that my air filter had come detached from the housing intake pipe. I replaced the filter and noticed dirt and dust around this intake pipe. So it is very possible that dirt has got onto the MAS.

I think my first action will be to access the MAS and clean it? Is the MAS also called a lambda sensor?

Thanks,

Nick

[Rockster]

Byakkonick said:

Thank you for your replies. Very informative! I think it could be something to do with the MAS because a few months ago I noticed that my air filter had come detached from the housing intake pipe. I replaced the filter and noticed dirt and dust around this intake pipe. So it is very possible that dirt has got onto the MAS.

I think my first action will be to access the MAS and clean it? Is the MAS also called a lambda sensor?

Thanks,

Nick

An incorrectly installed or compromised air filter which allows dust into the intake can certainly foul the MAF. The thin film design is quite forgiving but it was not designed to operate in unfiltered air. (On paved roads the dust content of the air averages 1mg/m^3. Obviously it can be much higher depending upon the road or the type of terrain the road runs through. (I've driven through dust so thick from a distance it looks like a muddy river flowing across the road.) In dustier conditions the dust content can be 40mg/m^3 and an engine could ingest up to 50 grams of dust over 1000km.)

In this case I think a cleaning of the MAF could be called for. Handle it with care. Clean with care. They are expensive to replace. If you drop it you break it. If you static discharge into a wire connector you break it. If you static discharge into the wiring harness connector you can ruin the DME. And if the MAF is expensive wait until you price a new DME... Get the picture? Be careful.

Lambda sensor refers to the oxygen sensor. The compare the oxygen content of the exhaust gases to outside air.

(The MAF sensor -- MAF stands for Mass Air Flow -- is there to measure the amount of air (its mass) so the DME can add the right amount of fuel to feed the engine the proper air/fuel mixture so the exhaust gases are of the ideal composition for processing by the converters.)