951mcomm

just got my car back from Porsche. They just completed a timing belt change. I drove the car and noticed the idle at @2000. Brought the care back to them they tell me it is a switch that needs to be replace ($1000 parts and labor). My question is 2 fold. First what switch could they be talking about. Second what else could it be (vacuum lines i do not know how or where to measure the vacuum). I am a novice at trying to diagnose issues. Any detailed help would be appreciated.

Carlsbergas

I smell bs about that switch

bumper87

Yeah BS for sure, its most likely a vacuum line off. Literally just pop the hood, look at the lines which are around the intake and follow them(there under it, beside it, one below the throttlebody etc). They should all lead somewhere and be connected.

Darwantae951

1000 rpm too high wouldn't lead me to the vacuum lines. First thing I'd check/test is the ISV.

Tom M'Guinn

There is a throttle position switch (TPS) that can go bad or be mis-adjusted and cause high idle. However, a steady 2k idle sounds more like vacuum leak than TPS. Either way, $1000 to replace the TPS is off the charts too expensive. Even if the shop charges $200/hr labor, the bill should still be a fraction of their quote. Ask them what switch is bad and how they confirmed it was bad? Regardless of the answer, I'd start looking for a new shop.

Tom M'Guinn

I was focusing more on the shop than the car problem, but agree its not likely solely a vacuum leak or even ISV, since the TPS should cut gas around 1600 and the idle would bounce rather that idle steady at 2k if the TPS 'switch' were closing.

Black51

Hey, I've been quoted ~$35 for ONE Bosch copper spark plug; the stock plug in these cars... at a Porsche dealership!!

Guess it's not too uncommon for some shops to be out of line on their pricing sometimes.

Black51

Have you checked the throttle cable for nicks, kinks, or frays?

Darwantae951

I've had my CC cable keep my engine at a high idle, before. Don't know why but I had to disconnect it and re-adjust (I never touched it before, either).

951mcomm

I went to the shop and they tell me it is a bad idle control valve. they 500 for the part and 500 for the labor. Should I clean it and reinstall? Just replace? Is it a tough job to do?

Tom M'Guinn

Is your car running at a steady 2k rpms at idle? If so, your TPS is probably not adjusted/connected properly or its broken. When the throttle switch closes and the rpms exceed about 1600 rpms, the injectors shut off completely. It's set up that way so the motor can return to idle quickly and efficiently when you let off the gas. So, it's possible your ISV is bad, but if the throttle is fully closed you should not get a steady 2k idle. I'd start by confirming the throttle switch is working. See clarks-garage for a full description on testing that.

The ISV is simple in theory. It simply routes air around the throttle place, as controlled by the computer to maintain the right rpms. Notice how the hoses are routed -- one port to suck in fresh air and the other to deliver it directly into the intake manifold. You can block off the hose and port to see if the car still revs. If it does, then the ISV is not your culprit. If it does not rev, then you might need to investigate further -- that could mean the ISV is the culprit, but not necessarily (you might just be blocking off the intended ISV air supply and replacing it with a leak to get a more normal idle speed).

Replacing the ISV isn't that hard, but you'll want to remove the intake manifold to get to it, which can be intimidating for a first-timer. See my head gasket write up linked below to see the steps involved. (You can ignore the steps after the intake if off...) I'm leery about the shop's diagnosis for the reasons above (at least as the sole cause of the issue). However, if you do need a new ISV, then $1000 is crazy high, but probably in keeping with dealer pricing as Black51 points out. For reference, a brand new Bosch ISV is about $200 at full retail, and for folks accustomed to working on these cars, it would take an hour, maybe two, to replace it working at reasonable pace...

951mcomm

ISV= idle control valve ? car does idle steady @2000 and the revs don't fall off quickly..

951mcomm

TPS? what is it, where do i find it, what to do with iot when i do?

Tom M'Guinn

Right, ISV is short for Idle Control Valve. You can read about it and how to replace it here:

http://www.clarks-garage.com/shop-manual/fuel-21.htm

I have a video somewhere showing how to test the ISV, which I'll post when I find it.

TPS is short for Throttle Position Switch. You can read about it, and how to test it here:

http://www.clarks-garage.com/shop-manual/fuel-06.htm

951mcomm

should i just replace or try to refurbish?