Engine Revving by itself - help

[Frank_Oj]

I would appreciate any help on this one.
I have a 98 Boxster and today it starting revving by itself. It is most noticeable when idling. It revs from 1200 to 1900 rpm every 2 seconds. It is constant from the moment I turn the engine on.

I will take it to a Porsche mechanic in the next few days, but was hoping someone could give me some advice/hints before I take it there. I am particular worried about the potential expense. Any ideas?

The car has travelled 36000km.

Thanks in advance.

[mrmickeymouse]

I believe I read somewhere [toolpants] who said this may be a software problem.

Do you have a check engine light [CEL].

Scott

[Frank_Oj]

The CE light is not on. But thanks on the tip on Toolpants postings. More hunting took me to the Renntech site and then a posting pca.org that said the following
http://www.pca.org/tech/tech_qa_question.asp?id={2FE2DB7F-066E-44BB-86B6-F94296717EDC}

Appreciate the help - at least when I take it to the mechanic I can lead them in the right direction.

"Usually the problem would be with a sluggish Idle stabilizer or also called an IACV. These valves can get corrosion in them and slow down until they get stuck and then cease to work. This valve controls the amount of controlled bypass air required to keep the car idling. These conditions change with load and the valve opens or closes to accommodate this. The valve is easy to access from its location on the side of the throttle valve housing. This condition will usually be exacerbated with the A.C. on."

[mrmickeymouse]

I did not think this was it due to you having an above normal idle and then idling higher.

Most of the posts I have read are idling between 0 - 1000 for the IACV.

Yours was out of that range. The PCA Tech answered as if the IACV was faulty. The IACV will choke your idle, if this is the IACV would you please tell me.

TIA,
Scott

[Tool Pants]

This was covered at our tech session yesterday, believe it or not.

This valve can stick, if that is your problem. You hit the throttle body with a soft hammer and see if the idle is then stable.

Then your try a bigger hammer.

[Frank_Oj]

Hmmm - good 1, won't be me weilding the hammer.

The normal idle was OK - around 1100rpm.

Scott - Thanks, sounds like the throttle and not the IACV.

This posting probably explains my problem better (assuming there is a typo in there and he means 1100-2000rpm & not 1100-200)
http://www.pca.org/tech/tech_qa_question.asp?id={FAF3756D-1D70-4DE2-B2FC-7AB8BD5F657A}

Thanks again. Will let you know what mechanic finds - and what size hammer he uses ;-).

[QporscheQ]

You hit the throttle body with a soft hammer and see if the idle is then stable.

Haha. At my office we call this a "Technical Tap." Its amazing how many things can be fixed by banging on them.

[PeterJoyce]

I have a question about my ideling. My 04 Boxster idles at 700 r/m. Sometimes the car shakes at stoplights lightly. Especially when the a/c is on. Does this seem like a low rev?

[mrmickeymouse]

Manual states-

Idle speed - manual transmission rpm 790

Scott

[Frank_Oj]

It ended up being the oil separator. Once this was replaced - all was back to normal. They mentioned that the 97-98 had a different kind of oil separator, which got changed in '99 to the one they installed for me now.
Thanks.