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-   -   PCM? What else could it possibly be? (http://www.saturnfans.com/forums/showthread.php?t=157892)

ch3no2 08-24-2010 11:20 AM

PCM? What else could it possibly be?
 
I have a '94 SL1 with a 5 speed manual trans that at first glance appears to have the classic Saturn high idle (1200 -1400 rpm) except that it refuses to be fixed. Instead of posting the entire horror story which would take more space then most would care to read I will skip the 6 months of code reading etc. and will list breifly what has been replaced or done. Hopefully someone will see something I have missed. Replaced....ECTS (twice), ECTS wiring, thermostat, TPS, IAC, EGR valve, EGR solenoid, Intake gasket, MAP sensor and most vacuum lines. Labor.....Proved there are no vacuum leaks by using a smoke machine, removed and cleaned throttle body, Cleaned or replaced every connection at sensors.
None of the sensors were replaced without having a code indicating it to be a problem at the time. I did find multiple vacuum leaks at first but to my suprise fixing them didn't help at all. The idle does sometimes go higher and stay there untill I come to a complete stop. IDoes anyone have any suggestions? Is there a way to test the PCM?

PurdueGuy 08-24-2010 11:35 AM

Re: PCM? What else could it possibly be?
 
Find a cheap junkyard & pick up a compatible PCM & swap it to see what happens. Bad PCMs are rare, but possible.

*edit* another thought - the idle is controlled by the PCM through the idle air control valve. You could unplug the IAC in the fully closed position and see if it still idles high.

madpogue 08-24-2010 11:48 AM

Re: PCM? What else could it possibly be?
 
[QUOTE=ch3no2;1652743]The idle does sometimes go higher and stay there untill I come to a complete stop.[/QUOTE] This is normal. If the idle is 800-ish when the car is not moving, and 1200-1400 when the car is coasting, it's idling exactly as it was designed and built to do when it rolled out of the overhead door at Spring Hill.

fdryer 08-24-2010 11:49 AM

Re: PCM? What else could it possibly be?
 
Wouldn't it be easier to block the little hole in front of the throttle plate? The one that provides supplemental air for the idle air control valve (IACV)?

madpogue 08-24-2010 12:25 PM

Re: PCM? What else could it possibly be?
 
[QUOTE=fdryer;1652753]Wouldn't it be easier to block the little hole in front of the throttle plate? The one that provides supplemental air for the idle air control valve (IACV)?[/QUOTE] Why? If the OP's statement implies that the idle returns to normal when the car comes to a stop, it's running perfectly, and there's nothing to "test".

OldNuc 08-24-2010 12:27 PM

Re: PCM? What else could it possibly be?
 
If it is not broke, don't fix it.

ch3no2 08-24-2010 01:16 PM

Re: PCM? What else could it possibly be?
 
Perhaps I wasn't clear enough in my post. The idle is never normal. When stopped it is at 1200 - 1400 rpm. It is sometimes higher than that, up to 2200 rpm untill I come to a complete stop, then it will go back down to 1200 - 1400 rpm. I did block off the port for the IAC but the idle didn't change. This made me think there has to be air getting in somewhere, but I couldn't find a vacuum leak and the smoke machine couldn't either.

fdryer 08-24-2010 01:27 PM

Re: PCM? What else could it possibly be?
 
With all the distractions aside, the high idle with the iacv port blocked does imply a vacuum leak. Possibly a vacuum line cracked but not visible like a brake boost vacuum line? Some had theirs fall off the intake manifold with revving to 4k rpm. Start looking in earnest for this leak.

OldNuc 08-24-2010 04:45 PM

Re: PCM? What else could it possibly be?
 
[QUOTE=ch3no2;1652783]Perhaps I wasn't clear enough in my post. The idle is never normal. When stopped it is at 1200 - 1400 rpm. It is sometimes higher than that, up to 2200 rpm untill I come to a complete stop, then it will go back down to 1200 - 1400 rpm. I did block off the port for the IAC but the idle didn't change. This made me think there has to be air getting in somewhere, but I couldn't find a vacuum leak and the smoke machine couldn't either.[/QUOTE]

Are you the original owner of this car? Take a look at he quadrant that the throttle cable runs on. There is a mechanical stop at the lower edge of it. There should be a cover on this stop screw, is there? Do not adjust this screw, it is factory set. The hose between the PCV valve and the manifold can crack below the larger cover over the hose. Pull the PCV out of the valve cover and put your finger over the open end with the engine running. Idle should drop and recover. Also check the hose carefully. same with the brake booster. To look for a vacuum leak get a squirt bottle full of water and drizzle it along the head/manifold joint, injectors where they enter the manifold, and the throttle body to manifold joint.

madpogue 08-24-2010 05:39 PM

Re: PCM? What else could it possibly be?
 
Sliiiight chance of a vacuum leak at the EGR valve as well, if the gasket happens to leak just on the intake side.

OldNuc 08-24-2010 05:41 PM

Re: PCM? What else could it possibly be?
 
True, it was not an absolutely all inclusive list. I was multitasking while typing...

ch3no2 08-26-2010 08:18 AM

Re: PCM? What else could it possibly be?
 
SOLVED!!!! You will never believe it! 6 months ago when the problem first started I thought it was a vacuum line that was always falling off. I figured I would do some routine maintenance that the car was due for and at the same time make up a new vacuum line. I replaced plugs, wires, filters, pcv valve etc. and made the new line. The idle was still high after and I remember thinking it was actually a little worse. I chased the problem until yesterday when I pulled out the PCV valve and put my finger over it. The idle returned to normal. I thought "could it be that simple?" I changed the PCV valve and the problem is GONE. I either got the wrong valve from the parts store or I got a defective one with the wrong orifice size. It looks identical to the new one. So it was a vacuum leak....sort of. Thanks to everyone who posted to help!

OldNuc 08-26-2010 09:10 AM

Re: PCM? What else could it possibly be?
 
Saturn is very picky about PCV valves. As you have noticed. They are not all the same inside and V-8 PCV looks exactly like a small 1.9L 4 cyl one except the floating plug inside the housing will never stop the flow. Periodically take the PCV off and wash it out with brake cleaner. Then shake it, does it rattle? If so it is still probably good. Now turn it over so the inner disk floats on the spring, does it jiggle like it was setting on jello when shaken gently? If so it is good, put it back.


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