Spontaneous high idles

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tibo
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Spontaneous high idles

Post by tibo »

I have been trying to hunt down the cause of my spontaneous high idles. The engine will idle well (~900rpm) but sometimes the engine will stumble a hundred RPM or so and MS3 will usually catch it without a problem. However, sometimes MS3 will recover far too greatly and cause a high idle of ~1750-2000rpm or so. MS3 then keeps the idle that high and does not let it lower, I have let the engine sit and idle that high for a minute, I have driven it around at varying engine rpms and even accelerated with the high idle always persisting. The only way I get it to stop is to shut the engine off and cycle power to MS3, after which it returns to normalcy and functions fine. I have not been able to datalog this as it is sporadic-some days it will not happen while other days it will happen multiple times. The MSQ is attached. I am using the closed loop idle settings with an idle air control motor from a GM LS engine. The engine itself is a fairly basic SBC, not an LS or LT series engine.
Matt Cramer
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Re: Spontaneous high idles

Post by Matt Cramer »

Can you also post a data log of the behavior? This will give us more to go on.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
subwoofer
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Re: Spontaneous high idles

Post by subwoofer »

Sure you don't have a sticky throttle linkage or throttle body? Happens to me all the time, though no fault of the MS. TPS indicates 3.5-4% when it happens, and in my case I know where the problem is, it's just a bit too much work to fix right now compared to the hassle it creates.
Joachim
1974 Jensen-Healey
1990 VW Caravelle Syncro - running MS3+X
2014 Ford Fiesta EcoBoost
tibo
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Joined: Fri Jun 04, 2004 9:24 am
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Re: Spontaneous high idles

Post by tibo »

I was finally able to datalog my spontaneous high idle, it took several drives to catch it. The high idle issue seems to begin at 437 seconds in. This datalog also shows some instantaneous high RPM spikes that I had not seen on my other datalogs, could the two be related? I may try cleaning up the tach signal or increasing the noise filter strength for the tach signal.

***** The file I am attempting to post is receiving the message "The file is too big, maximum allowed size is 1 MiB." Anyway I can reduce this .msl file or post it somewhere to host it?
JAM
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Re: Spontaneous high idles

Post by JAM »

you should be able to edit the datalog to show just the section you are having issues, that should reduce the file size and you can attach it
tibo
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Joined: Fri Jun 04, 2004 9:24 am
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Re: Spontaneous high idles

Post by tibo »

Found out how to edit/trim the log file. Sweet! Never knew about that feature, great feature! Any way hopefully you guys can take a look.
Matt Cramer
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Re: Spontaneous high idles

Post by Matt Cramer »

I don't think the RPM spikes are related.

Try increasing the "RPM with valve open" settings to somewhere around 1800 - it appears this may be set too low.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
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