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Old 07-12-2006, 12:56 AM   #1
Larry Horne
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1996 SL2
Default No Fast Idle on Cold Start Up and Strange Idle There After

This is a continuation to a recent post that I did not get too many replys.

Since the other day when I installed a remote 12V outlet in my 1996 SL2 (1997 engine) the idle has be crazy. Sometimes right most often not.

Ususally its low about 500 - 550. I dont get that little increase in rpm at cold start now either. I've reset the idle according to Wolfman's instructions and no change. I've done his tap test on the TPS and no change. I've sprayed TBC on the manifold and hoses, no change. (I see vacuum recommended as a possible problem in a lot of replys but I dont see that many vacuum lines on this car. EGR is electric, cant tell how the fuel pressure regulator functions because I cannot find it.

Today the idling problem worsened. Coasting at 60 with the car in neutral it idled at 3100 with AC off, 2800 with A/C on. I know the PCM manages the idle setting when the car is moving and keeps the RPMs up in order to not drag on the engine when its placed back in gear. Try this test at 30 to 40 the RPMs settle smoothly to 1500 or so. Some times I barely have enough braking capacity to stop and pull into shops because the engine is idleing too high.

I've disconnected the TPS at idle and it does not seem to make any difference in engine performance, I rev it and it does about the same as when connected. (of course the SES light can on as expected due to diconnecting).

I'm loss. Do I try a new TPS? I've replaced everything else as the form suggests: new brass ECTS (cleaned plug), new T stat, plugs. wires, pvc (all OEM), cleaned the TB/IAC/TPS and EGR valve.

This all happened 2 weeks ago when I installed the 12v outlets. The only thing that went wrong that day was I nicked a wire bundle uder the console with the drill bite but I have inspected all wires and ensured conductivity of the leads.

HELP......new TPS? what about fuel? Fuel Pressure Regulator? Where is it. My Haynes manual does a poor job of showing it. Maybe the IAC?

Plan on testing the TPS and IAC voltages next.

Car runs fine at speed, its just not returning the idle at the currect rate the car is decelerating if that makes sense.

HELP, Anyone......
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Old 07-12-2006, 05:48 AM   #2
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2003 L-Series 3.0L Sedan
Default Re: No Fast Idle on Cold Start Up and Strange Idle There After

Not being familiar with the S-series, all fuel injection management electronics share similar components to provide the basics; ignition timing, ignition and fuel injection pulses. Its the peripheral hardware that provide additional signal input/support to the engine management system that rears its ugly head and creates troublesome fault isolation techniques that are beyond the realm of the best factory created troubleshooting flowcharts. It seems to be at this point in your path to resolving this not-so-normal engine running problem that there are several ways to go.

Your in-depth inspection of the TPS and IAC will help as long as you stay aware of this abnormal symptom. I've read up on your symptoms and I think you've narrowed it down (for now anyway). Since I will go out on a limb and state that L and S series cars use similar idle air control valves (IAC) that are electronically controlled by the PCM then I'm wondering if your IAC is causing the symptoms. Without re-printing the FSM description of the IAC this "two coil stepper motor moves a pintle valve in and out from the seat controlling the amount of air entering the intake manifold. How far the valve is opened is determined is based on engine speed, a/c relay command, ECTS, TP angle, transaxle range switch position, and transaxle shifting. Once the PCM learns the IAC position for a/c relay on or off it can retard or advance ignition timing to finely adjust the idle speed without moving the IAC valve".

It wouldn't be too hard to imagine when given a long time for components to age from heat, cold, and vibration that wiring, wiring connectors, electric servo motors, and solenoids will eventually act up at some point in time to contribute to the new backyard mechanics experiences, as well as the certified ones working at the dealerships. Trial and error, and experience.

1-The lack of the cold start higher idle seems to point to this IAC valve. Since the PCM has to have the ECTS as one of its inputs (that you've replaced) and ruling out the PCM then there should have been a return to the cold start high idle until the engine warmed up. This didn't occur.

2-The engine idling very high when at 60 mph (xmission in neutral) or 30-to-40 and never returning when the engine management system is supposed to decrease the rpm's makes me think that one of the two stepper motors controlling the idle air valve is inoperative while the throttle plate is closed. The two motors are independently controlled by the PCM and basically are in a tug-of-war fighting to open and close the idle valve. Staying open fits the description you have. It then seems that the other stepper motor is either disconnected to the PCM or is defective. This stepper motor should return the idle valve to the closed position thereby reducing the rpms.

3-Keeping in mind that the throttle is separate from the idle air control valve can best be described as the IAC fine tunes the idle speed all the time while the throttle plate is closed. The IAC is a bypass tunnel for the intake air for emissions control and a/c fine engine speed control, to name a few reasons for its existence.

4-Look at the connection to the IAC adjacent to the throttle body and see if the connection is loose or if the wiring is worn, frayed, etc. If it is the IAC and you replace it be sure to readjust the throttle stop screw back to where it should be.

Armed with a little more info I hope this helps you, at least let everyone know if you've resolved this problem with or without my input.
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Old 07-12-2006, 09:11 AM   #3
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1996 SL2
Default Re: No Fast Idle on Cold Start Up and Strange Idle There After

Any idea what the procedure is for installing a new IAC? My Haynes manual uses the same dimension from tip of pendle to seating surface for both the MPFI and TBI units, (its a 1991-2000 coverage on the book)

Thanks
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Old 07-12-2006, 11:06 AM   #4
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Default Re: No Fast Idle on Cold Start Up and Strange Idle There After

Quote:
Originally Posted by Larry Horne
This all happened 2 weeks ago when I installed the 12v outlets. The only thing that went wrong that day was I nicked a wire bundle uder the console with the drill bite but I have inspected all wires and ensured conductivity of the leads.
I would go back to this point and check things over since the problems started here. Check all the fuses in BOTH fuse boxes, under hood and inside car. Check for connectors pulled loose near where you were working. Check/clean/tighten all grounds.

Throwing parts at it is probably the wrong approach.

If necessary take it in to the dealer and tell them what you were doing when it all turned to crap.
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Old 07-12-2006, 05:31 PM   #5
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1996 SL2
Default Re: No Fast Idle on Cold Start Up and Strange Idle There After

Good call on the fuses, I could have blown one and not noticed. I'll check both boxes when I get home.

I'm not quite to the point of taking it to a dealer for this. Thats kinda like going to the doctor and telling him your toe nail hurts when you squint.......I'd end up having to leave them the title to cover the bill. LOL

I've verified continuity throught he wires in the bundle under the dash and center console. Seriously, you could barely tell where I touched the insulation.

I'm fairly certain its a coincidence with all of the other similar posts on the forum with almost exact symptoms.

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Old 07-12-2006, 06:44 PM   #6
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Default Re: No Fast Idle on Cold Start Up and Strange Idle There After

Quote:
Originally Posted by Larry Horne
Any idea what the procedure is for installing a new IAC? My Haynes manual uses the same dimension from tip of pendle to seating surface for both the MPFI and TBI units, (its a 1991-2000 coverage on the book)
Thanks
Ok here's the scanned text/pictures on two pages;IAC.GIF

IAC 001.GIF
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Old 07-12-2006, 06:53 PM   #7
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1996 SW2
Default Re: No Fast Idle on Cold Start Up and Strange Idle There After

That looks suspiciously like a TBI car.
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Old 07-13-2006, 09:40 PM   #8
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1996 SL2
Default Re: No Fast Idle on Cold Start Up and Strange Idle There After

First, all fuses, grounds, plugs checked satisfactory.
Second, my manual has the same instructions for TBI and MPFI, so I'm guessing they are the same dimension on the pendle length.



Status, the car is running ok, but still no decent cold idle....I'm going to reset the idle speed IAW Wolfman's instructions and see if it makes any difference.

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Old 07-14-2006, 01:30 AM   #9
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Default Re: No Fast Idle on Cold Start Up and Strange Idle There After

An EASY (and free) test of the IAC valve...

With the engine idling at the odd LOW level and with the air-snorkle OFF the throttle body, cover the IAC air port on the floor of the throttle body (the port you plugged when you set the idle speed) if the idle speed does not drop noticeably (probably stall the engine) when you cover the port, the IAC valve is the cause of the low and erratic idle. REPLACE IT.
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Old 07-15-2006, 12:33 AM   #10
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1996 SL2
Default Re: No Fast Idle on Cold Start Up and Strange Idle There After

Wolfman can you verify the measure from end of pendel to seating service?
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Old 07-15-2006, 12:39 AM   #11
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Default Re: No Fast Idle on Cold Start Up and Strange Idle There After

A new OEM IAC valve should be set and ready to install right out of the box. I cannot recall ever having to measure/adjust one, though I do not know the "proper length" measurement right off the top of my head, if I ever found one off spec when removed, I REPLACED it. The IAC valve should never go off spec (at rest) unless it has a internal problem with the step motor that operates it, which means, you guessed it, you need a new IAC valve.
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Old 07-21-2006, 03:18 PM   #12
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1996 SL2
Default Re: No Fast Idle on Cold Start Up and Strange Idle There After

Quote:
Originally Posted by wolfman
A new OEM IAC valve should be set and ready to install right out of the box. I cannot recall ever having to measure/adjust one, though I do not know the "proper length" measurement right off the top of my head, if I ever found one off spec when removed, I REPLACED it. The IAC valve should never go off spec (at rest) unless it has a internal problem with the step motor that operates it, which means, you guessed it, you need a new IAC valve.

Wolfman,

I can see from the packaging of the new IAC that the length is set at the factory. I'm planning on installing it as is.

I still have that unusual high rev or idle when the car is going 60 mph or so. That is if I shift to neutral whil the car is coasting from 60, the engine holds its revs at 2900 to 3000 rpm. I replaced the ECTS and no difference.....

I'll let you know what happens.

Thanks
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