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Autocross/Hillclimbs
 
Join Date: Oct 2012
Location: Wilsonville OR
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Intermittent Idle surge and pegged oil pressure

They frankly started about the same time but I can't imagine they're related. Here's a short history - bought the car a month ago. Wires to oil pressure sender looked cut. I hooked them up, gauge worked great! Week and a half later few days ago) it starts pegging with the key on again. Like a gremlin swapped the wires backwards, but clearly that's not the issue because it worked until one morning.
Since I bought the car, it idles about 1000 cold, and 1500 hot. Which is odd. Also when I push the clutch in coming to a stop, the idle dips to around 5-700 then bounces back and stabilizes. Well now recently I've developed an idle surge sometimes. Last night it was when it was cold and after heating up it was fine. Then I parked it and next time it was cold the surge was gone. Today I drove it 30 miles no issues, got a burger, car off, ate, turned car back on (still warm) had the surge for about 5 min. Appears smooth now.

What in the world?!

Sound like an iacv problem? The OPS issue seems electrical because it pegs car off ignition on. or a problem with the actual OPSU. Likely not related

Old 11-02-2012, 01:25 PM
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OPSU. Common problem. One wire goes to the red light, the other runs the gauge. Don't waste your time (or money) with a non-OEM sender. Search is your friend.
Ps - check your vacuum lines. They are probably 25+ years old. Buy a kit from our benefactor and change them all.
Old 11-02-2012, 01:30 PM
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Call Sunset Porsche in Oregon, they have the OEM Genuine Porsche VDO sending unit at a gooooood discount. I got it from them and happiness ensued.
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Old 11-02-2012, 01:45 PM
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Autocross/Hillclimbs
 
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If I hold off on the OPSU are there any issues it can cause? I still have a $200 title transfer, and timing belt change taking priority

Vac leak is probable, I noticed today that the brakes effect it. i just went through with throttle body cleaner and sprayed every joint and vac line i could find and got nothing... ideas?

My oil light works but is not on. If the OPSU was bad would it be on?

Thanks for thereplies!

Last edited by PDX-944; 11-02-2012 at 06:36 PM..
Old 11-02-2012, 06:08 PM
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I have a pegged gauge because I haven't yet installed the replacement. My oil light doesn't go on though. Only with the main lights on at idle does it come on.
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Old 11-02-2012, 07:09 PM
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Autocross/Hillclimbs
 
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hm. mine never comes on except while starting the car.
im thinking my iacv (ICV, ISV) may be the problem here with the idle
Old 11-02-2012, 07:25 PM
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I have heard cleaning the Idle control valve can help. Someone else also mentioned to me checking my throttle position switch because I too had a weird surging idle. It has happened three times out of the entire time I have owned the car, happened like a week ago and hasn't happened since then. All new vacuum hose from Lindsey racing helped a lot.
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Old 11-02-2012, 08:42 PM
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Autocross/Hillclimbs
 
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heres another strange symptom:

if im sitting, idling at 1500rpm (no surge), and i tap the gas - not enough to actually rev it - it will drop to 1000rpm idle. still smooth. if i tap it again, it will jump up to 1500 and idle smooth. then if i tap it again, it will drop and idle at 1000... and so on. just keep tapping it, and it will go back and forth between idle speeds.
Old 11-03-2012, 10:42 PM
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Try this - when you get it idling in 'high' mode, see if you can go under the hood and manually force the throttle to close a little more.

I assume this is an NA? It's helpful to put your car in the signature line so we don't start thinking about issues with the dynamic idle control for the 16V engines, say.
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Old 11-04-2012, 06:19 AM
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Autocross/Hillclimbs
 
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good call. if i cant then its pretty much gotta be the iacv right?
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Old 11-04-2012, 08:20 AM
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Autocross/Hillclimbs
 
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Went at it one more time with starting fluid. Found a leak in my intake mani gasket at one port. Could that be my surge?

Also upon high idle I can pull back on the pedal or cable and it lowers the idle. Cable issue or spring issue? It doesn't stick otherwise
Old 11-04-2012, 01:14 PM
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Yeah, you'll want to correct both of those things.
The throttle not closing all the way might be the throttle plate ('butterfly') rubbing in the throttle body bore (was for me). But could just be all gunked up.
I think if it were me I'd pull the intake to replace the gasket and rebuild he throttle (there are kits for the throttle).
And while you're at it inspect and replace some hard to get to vacuum lines.
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Last edited by gtroth; 11-04-2012 at 04:16 PM..
Old 11-04-2012, 04:11 PM
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Make sure the throttle cable is adjusted correctly. Check to see if there is any interference at the throttle pivot point.Sometimes there is a clamp that willcatch on the pivot.
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Old 11-04-2012, 04:38 PM
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Autocross/Hillclimbs
 
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I will check those out when I do it. Im worried about the j tube, it's pretty old and brittle it looks like. I'm nervous to pull it off right now to clean the tb because if it cracks ill be in a bit of a pickle!
Ill wait til I'm at my shop tomorrow.
Anything else to do while intake mani is off?

Old 11-04-2012, 07:48 PM
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