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Dtc 31 1990 Ls400 (Code 31)


Exhaustgases

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Engine would run okay cold at all speeds. Then at idle would want to die after warm up it would need at least 1300 or so RPM's to keep running and would not idle. No CEL set but had DTC 31 set.

DTC = Diagnostic trouble code.

I think the reason it ran good cold is because of open loop, and running on idle air control.

The air meter checked good for resistance value, and what I found was a really bad plugged air filter. So far with not much running time it seems better. Makes sense since who knows what extra turbulence or lack there of the Karman vortex sensor is seeing with a plugged air filter.

And note never ever try to clean these sensors. If you need to clean the airflow straightening screen that feeds the sensor, remove the sensor. It is easy to goof it up putting it back in, so when doing that remove the whole assembly so you can look in and see to make sure it fits in the lower counter bore in the aluminum body. The sensor has small holes that let the pulsations enter to vibrate a mirror so no chemicals or dirt allowed in them. And be careful there are a couple of orings under the top mount point.

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Engine would run okay cold at all speeds. Then at idle would want to die after warm up it would need at least 1300 or so RPM's to keep running and would not idle. No CEL set but had DTC 31 set.

DTC = Diagnostic trouble code.

I think the reason it ran good cold is because of open loop, and running on idle air control.

The air meter checked good for resistance value, and what I found was a really bad plugged air filter. So far with not much running time it seems better. Makes sense since who knows what extra turbulence or lack there of the Karman vortex sensor is seeing with a plugged air filter.

And note never ever try to clean these sensors. If you need to clean the airflow straightening screen that feeds the sensor, remove the sensor. It is easy to goof it up putting it back in, so when doing that remove the whole assembly so you can look in and see to make sure it fits in the lower counter bore in the aluminum body. The sensor has small holes that let the pulsations enter to vibrate a mirror so no chemicals or dirt allowed in them. And be careful there are a couple of orings under the top mount point.

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I think that I had something similar happen today to my 1998 LS 400. In the 110,000 miles that I have put on this thing the only problems I've had are one exhaust sensor went bad and I'm on my third starter motor. What moron decided to put the starter in the valley between the heads? IDIOT!!!.

OK back to todays problem. First thing today I drove 34 miles to the doctor. After a 30 minute appointment I started to drive home. At the first stop light the engine died....started back up with no problem. At the next light..same thing and so on and so on at every light. After 20 minutes driving at 50+ mph all of a sudden a sound like the recap coming off a cheap tire started. It sounded like it was coming from the passenger side front tire. It lasted maybe 6 or 7 seconds and then it was gone. Kept driving with no problems and then about 10 miles later the same horrendous sounds. This time it lasted 10 or 15 seconds. I pulled over crawled all over the car but didn't find anything. But now the engine doesn't die at idle. Fired it back up, drove the last 5 miles to get home and no problems. I have looked this vehicle over and have found nothing loose, leaking, out of place......nothing!. I disconnected the battery for 30 minutes trying to do a minor reboot on the computer.

Not having access to a diagnostic computer I have no idea what code it threw. If anyone has ideas, I would love to hear them......thanks.

Flash

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The Idle Air Controls (ICL) tend to gum up and that is what supports your idle control as it adds fuel to idle (until it gums up) to make car idle well. Not an easy thing to remove as it is under the throttle body so I take of the air tubing and spray cleaner in the inlet where I saw on youtube and it works for awhile, Not a bad idea to add some seafoam or another good fuel system clear either. Not that unusual a problem on these with miles.

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VBdenny...thank you. I'll be under the hood tomorrow and follow your suggestions. Oh, how I miss the days of the '50's and '60's Chevys. You could fix anything and keep it running with a 1/2", 9/16", 5/8" wrenches, a couple of screwdrivers and a matchbook for a feeler gauge. I used to ride old motorcycles.....pretty simple macines......then I bought an '09 H-D Sportster. What a shock....electric start, turn signals, hydraulic disc brakes, fuel injection, electronic gauges, theft alarm and all sorts of things that made my simple mind swim. The point of this is just this.....it sure was easier to keep a car running when you could diagnose things without having to plug it into a NASA mainframe. Thanks for pointing me in the right direction.

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Wow third starter and such low miles. Cadillac's do the same thing on the Northstar I think. It is in a great place it stays warm and toasty, Its so easy to get to a guy on another web site says he can do it in an hour or so I think??? It was good engineering actually I think its to keep mechanics employed.

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Balance the engine? As in harmonics or so that it can turn high RPM's without vibrations or balance it's center of gravity so that when you use a hoist to lift it out of the frame it hangs level? A starter motor is something that has a limited life expectancy and to put in under the intake manifold is asinine. I can't think of any other engine manufacturer that places the starter there.

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Balance the engine? As in harmonics or so that it can turn high RPM's without vibrations or balance it's center of gravity so that when you use a hoist to lift it out of the frame it hangs level? A starter motor is something that has a limited life expectancy and to put in under the intake manifold is asinine. I can't think of any other engine manufacturer that places the starter there.

Hello !!! read my post above...................

And looky here

https://www.youtube.com/watch?v=L-OvSyLwVnw

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+1 on the idle air control valve. Might as well clean the throttle body too. But DO NOT MOVE OR REMOVE THE THROTTLE POSITION SENSOR. You will play hell getting it back to where it needs to be. My car idles low now around 400rpm unless my a.c. is on and when I turn the wheel it bogs down even less. I'm almost at 112k miles. I'm going to clean the throttle body and iacv one of these days

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