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1997 idles unevenly, sometimes dies

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1997 Boxster with 34K miles, manual transmission.  It has developed a problem where is idles unevenly,  cycling between 400-maybe 1100 RPM, and if left alone long enough, will stall out.  No codes are read with my BlueDriver OBDC2 reader.  I changed the oil about 600 miles ago, and cleaned the TB when this rough idling began, but no success in fixing the problem.  I don't have access to any of the Porsche diagnostic tools. 

Any pointers to help diagnose the problem or things to try to fix it?  Thanks



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3 hours ago, amegarth said:

Simple first.  check for a leak at oil filler. Or dip stick or fuel filler any vacuum leak can cause rough idle. 

It sat all winter and the only thing on the ground was 1-2 drops of oil on the ground.  Dont think that would qualify as a leak.  dipstick OK.  I doubt fuel filter...haven't touched it.

Chasing a vacuum leak is a PITA...lol




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  • 2 weeks later...
  • 2 months later...

Did  you get this fixed? 

I was having trouble with car not idling at start up when cold. Removed throttle body and cleaned idle valve (1998 2.5l). It was gunked up and little metal "sliding door" was jammed.  Got it loosened up well. This morning the cold idle is fine.

But. After 10 mins of town driving it idled erratically and cut out several times. Took it for a good hard drive after which its running smoothly. 


If the erratic idle comes back my first check will be vacuum leak:

during plenum reinstall I struggled with the thin pipe that slips into one of the rubber boots. 

Also re-used the gaskets... may be leaks there.


Sorry for my long story and hijack. Maybe it helps.


Regarding idle valve (IAV, ICV): what I learnt: to check its function, remove from TB, apply positive voltage to central pin and negative to either of the side pins. Small 9v battery is fine,  don't need 12v.

Valve should flick open and shut with one and the other.

With no current applied, mine was open just about 2mm. 

Mine was seized up. Soaked with WD40, cleaned with cotton buds, jiggled witb small screwdriver until it came loose and moved easily. 


Hope you came right.

Hoping mine's fixed.



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On 9/20/2020 at 6:33 AM, Christoph Soltau said:

Did  you get this fixed? 




yes, after going over everything that I touched when I cleaned the TB, it still was running bad.  Took it to the local porsche indi guru.  It turns out that the pipe from the airfilter to the MAF was broken.  Very strange failure according to the mechanic.  He fit it back together and now I am on a hunt for a replacement pipe.  According to the mechanic, the pipe is sold in combo with the MAF so it is not cheap.  I have to do some searching. 


I suspect the broken pipe was the original problem, and not the TB but the TB was due for a cleaning anyway so it wasn't wasted effort.

Glad you got your problem fixed.


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