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Old 02-09-2007, 07:55 PM   #1
bobkane
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Default high idle - slow rev-down

Hey Gang,

So now I'm the proud owner of a 2dn Saturn. My first is a '93 SL1 - I rebuilt the engine (in the frame) last summer and found the car to be a blast to work on and Saturnfans to be the most valuable resource ever. Just got done replacing the clutch. I think I need to do the control arms some day but otherwise it is a solid dependable 38MPG daily driver!

So now I am the proud owner of a '94 SL1 (charcoal just like the first). With 4 teenage boys I may just end up with four or more of these cars! I plan to do a engine rebuild this summer if I decide that the timing chain has to be replaced (it seems to be very slightly rattling - but it is pretty quiet so I'm not panicked).

The car had a high idle when I bought it, and the revs go down slowly (between shifts, etc). I'm figuring that this is some problem with the vacuum hoses to the engine controller and plan to putt the airbox and make sure all are in good shape. I'll also clean (and perhaps replace) the pcv valve. Any other suggestions for the short term?

Thanks to all who so freely share their expertise. perhaps someday I will have gained enough experience to help (or at least encourage) a newbie like myself.

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Old 02-09-2007, 08:47 PM   #2
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Default Re: high idle - slow rev-down

May I suggest reading about the intake air control (IAC) valve as I believe that is contributing to the slow return of the high idle between shifts. Its a servo motor that doesn't move freely when not powered and one side of the motor may be sticking from long term build up of dirt from the intake manifold. Possibly soaking or cleaning with contact cleaner may help otherwise replacement would be the last choice unless you have a known good spare to substitute with.

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Old 02-10-2007, 02:09 AM   #3
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Default Re: high idle - slow rev-down

PCM coolant temp sensor and possibly the connector for it.

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Old 02-10-2007, 11:16 AM   #4
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Default Re: high idle - slow rev-down

I have a 96 SC2 that has basically the same symptoms. High idle, upshift light stays on between shifts (RPM's don't drop either), and if I am cruising, but remove my foot from the gas pedal the light stays on and the engine still "pulls" some.

Although, if I pull up on the gas pedal, the idle drops, upshift light goes out, etc. I've checked the return spring, cleaned the throttle body, etc. and have determined that most likely the throttle cable is the culprit.

the replacement cable came in this week, so in about an hour, I'm going to go out and see if this is in fact the problem. I'll let you know if that solves it.

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Old 02-10-2007, 03:01 PM   #5
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Default Re: high idle - slow rev-down

OK - Here is what I have found.

After replacing the throttle cable, the gap in the throttle body was the same or slightly larger. The idle was actually higher than before. I could push the throttle body closed, but as soon as I let go, it would open back up. So I went back and checked all of my cable connections. It was then that I noticed that there is a piece of plastic similar to a cable tie that runs through the gas pedal, with a "block" on the back side of the pedal. This "block" has tabs on the side, and can be moved along the plastic strip.

Well, once I moved the "block" away from the gas pedal slightly, the cable released, the throttle body closed, and all is well with my SC2. This is apparently an adjustment piece to allow for possible (or inevitable) throttle cable stretching. I must have bumped this piece while I was changing the cable. Anyway, I'd check this piece to see if it might be the cause of your high idle.

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Old 02-12-2007, 03:36 PM   #6
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Default Re: high idle - slow rev-down

the PCM has an automatic reving device that allows the RPMs to stay high between shifts so there is a smoother grab with the clutch...i read this in my owner's manual

if it is really high then there might be a problem in your intake and exhaust system. did you install something that reduces back pressure? cuz i installed a straight through muffler and i get the high idle problem, because less backpressure confuses my PCM

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