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Old 09-06-2009, 11:06 PM   #1
sr20fd3st
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Default '99 SW2 sometimes stalls as RPMs return to idle

About 6000 miles ago I rebuilt the bottom end (rings, bearings). It ran fine but burned so much oil due to the junkyard head I threw on it and its rotted valve stem seals.

About 500 miles ago I fitted my head with new valve stem seals because it was blowing more smoke that I did back in highschool. New PCV valve, EGR gasket, valve cover (snapped half those damn bolts off the old one). It started fine. NEVER have I had a starting problem. Compression is as good as can be. Starts within half a crank. Has great power.

Recently, everytime I come to a light or coast down a hill, when I put it in neutral and let off the gas the needle will drop from the 3k or whatever to about 500 or 600 for about 1-2 seconds and the lights will dim. Then the needle will jump to about 1100 and then quickly go to 900 where it sits and idles just fine. Anytime the RPMS drop in neutral, the car feels like it is going to stall but catches itself right before it does.

It's really nerve wrecking because I'm always thinking "god is it gonna stall this time?" It HAS stalled maybe once every 20 times or so. When it does, it starts back up just fine.

It also seems to do it so precisely the same everytime. RPMS drop, go to 500, jump to 1100, then settle at 900. Makes me think it's idle control acting up, vacuum leak, map sensor or other computer controlled component malfunctioning. I'm ready to adjust butterfly closed position just to keep idle up high enough, but I want a real fix, not ghetto rigged.

Any help would be great!

Thanks,
Oliver

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Old 09-07-2009, 12:00 AM   #2
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Default Re: '99 SW2 sometimes stalls as RPMs return to idle

Can we assume that the coolant sensor was replaced to eliminate this from causing any rich running issues? If so then you may have to consider cleaning the throttle body and if this was done then it may be a sticking idle air control valve (IACV). The iacv adjusts the engine idling speed from cold start through warm up and deceleration from speed. Since you haven't mentioned any idling, hesitation, balking, stalling, acceleration issues and described basically a working iacv (erratically), it may be a slightly dirty iacv that can be removed for general cleaning. Please be sure that the throttle stop screw has never been meddled with as it has no control after initial factory adjustments. Meddling with it may ruin control for idle speed as control is all from the PCM and no longer where the throttle stop was adjusted unless adjusted incorrectly. Having the throttle in a completely closed position may cause this condition as the throttle plate is never fully closed when the engine is stopped or idling. The iacv fine tunes idle speed from commands coming from the PCM.

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Old 09-07-2009, 02:19 PM   #3
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Default Re: '99 SW2 sometimes stalls as RPMs return to idle

I have not replaced the coolant temp sensor. First things first I will check the connection to it, as well as check the throttle plate closed position to make sure it's slightly cracked. What are the specs for throttle plate closed position?

I will also clean out the IAC and check it's connection.

My coolant is full, no air in system. Temp gauge reads normal (at first hash mark).

Did not know coolant sensor was so vital on this car.

Stickin IAC seems most probable, like it's not reacting fast enough.

Thanks for the tips! I will get back with an update on the situation.

-Oliver

To add:
My CEL has been on for a while for bad 02 sensor readings for a very long time (long before any of these problems occured). They are due to the fact that I replaced my Cat. with a piece of straight pipe lol. It's something I have to fix soon as I am scheduled for an emissions check soon.

You mentioned a faultycoolant temp sensor causing rich conditions...if I am running rich (surely am) it's most likely from the 02 sensor system.

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Old 09-07-2009, 02:37 PM   #4
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Default Re: '99 SW2 sometimes stalls as RPMs return to idle

Quote:
Originally Posted by sr20fd3st View Post
You mentioned a faultycoolant temp sensor causing rich conditions...if I am running rich (surely am) it's most likely from the 02 sensor system.
Its most likely bc of the bad ECTS in your car. Replace it.

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Old 09-07-2009, 03:10 PM   #5
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Default Re: '99 SW2 sometimes stalls as RPMs return to idle

Quote:
Originally Posted by sr20fd3st View Post
I have not replaced the coolant temp sensor....Did not know coolant sensor was so vital on this car....My CEL has been on for a while for bad 02 sensor readings for a very long time (long before any of these problems occured). They are due to the fact that I replaced my Cat. with a piece of straight pipe lol. It's something I have to fix soon as I am scheduled for an emissions check soon.

You mentioned a faultycoolant temp sensor causing rich conditions...if I am running rich (surely am) it's most likely from the 02 sensor system.
BIG mistake not paying attention to suggestions and making assumptions. Ignoring the coolant sensor and your last statement (bolded) can't be any more wrong. The O2 sensor sees the end result of combustion and although can alter the air/fuel ratios, is not the cause of a rich running engine. The main cause of rich mixtures is from ignoring this little coolant sensor. The original ones fail and cause rich running. Read all the past treads for the S-series cars. Ignoring replacement and you're already chasing your tail with little understanding of EFI systems.

The empty catcon that triggers the O2 sensor fault is your decision with a simple solution; fix it with either something jury rigged without the cat to turn the light off or put one on long enough to turn off the CEL to pass inspection.

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Old 09-07-2009, 07:26 PM   #6
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Default Re: '99 SW2 sometimes stalls as RPMs return to idle

Quote:
Originally Posted by sr20fd3st View Post
My coolant is full, no air in system. Temp gauge reads normal (at first hash mark).
Your thermostat is also stuck open, causing your car to run rich. Typical problem with these cars. Replace it, its very simple. 10 min job.

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Old 09-07-2009, 07:54 PM   #7
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Default Re: '99 SW2 sometimes stalls as RPMs return to idle

Cleaned out IAC...disconnnected battery to reset computer. Figured it would zero out IAC. Everything works fine now.


So whats the normal operating temp supposed to be ? (on the gauge that is)

You said my thermostat is stuck open...so I'm assuming the first hashmark is way too cold. The fans never come on...which I guess is a decent indicator the motor is not getting hot enough. Not to mention I can let it run for a while and the coolant seems to be only simmering in the coolant tank, not getting as hot as I think it should.

Should the coolant temp be pointing to the second hash mark? straight up?

Thanks,
Oliver

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Old 09-10-2009, 09:05 AM   #8
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Default Re: '99 SW2 sometimes stalls as RPMs return to idle

I had this problem with my '97 SC2, it was stalling at red lights.
I cleaned the throttle body and Idle Air Control per richpin's video and the idle and general throttle response is WAY improved.
While the throttle body was removed I noticed that the inside of the intake manifold was totally coated with oil sludge/gook. I cleaned it out with a rag, as far as I could reach. I'm thinking this could be a result of a long period of running with a bad PVC?

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Old 09-10-2009, 10:01 AM   #9
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Default Re: '99 SW2 sometimes stalls as RPMs return to idle

The sludge build up isn't due from any 'bad' pcv valve; the only purpose of the positive crankcase ventilation valve is to allow all the combustion blowby gases to ventilate through the valve to be inducted into the intake system for reburning. Every intake manifold will have this build up; what do you think will occur when constant blowby gases with burned/unburned combustion byproducts begins to coat the interior of everything it comes into contact with? It'll stick and eventually coat the interior and build up into what you now see. If you never looked into the intake manifold system you'd never know it and won't notice anything out of the ordinary as this doesn't affect engine running at all. In the old days the pcv valve wasn't used and the gases simply vented to the atmosphere. EPA/tree huggers/environmentalists/politics has regulated engine byproducts so we're required to recycle the blowby gases back into the engine.

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Old 09-10-2009, 05:43 PM   #10
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Default Re: '99 SW2 sometimes stalls as RPMs return to idle

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EPA/tree huggers/environmentalists/politics
basically anyone that is a far-left liberal.

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Old 09-11-2009, 01:19 PM   #11
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Default Re: '99 SW2 sometimes stalls as RPMs return to idle

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Quote:
Originally Posted by fdryer
EPA/tree huggers/environmentalists/politics
basically anyone that is a far-left liberal.
...The list describes me and I'm hardly a liberal -- I think Pres Reagan was by far the best we've ever had but he was a bit pink for me.

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