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Old 12-29-2014, 04:59 AM   #1
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Default PWM Idle Duty stuck at 41.2

After a year of everything going great, over the last month my '93 Eunos with Reverant's MS2 Basic has started having a high idle (around 1400 rpm), even when warmed up. Logs show that the PWM Idle Duty is stuck at 41.2 when it should be around 32 when warmed up.

Any idea how I can diagnose what has gone wrong? I've tried old maps, closed loop idle control, open loop idle control, etc. The idle valve tester in TunerStudio shows that the idle valve is working ok, it's just that the Megasquirt keeps asking for a value of 41.2 :(
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Old 12-29-2014, 08:17 AM   #2
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What is your value for closed IAC DC?
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Old 12-29-2014, 08:48 AM   #3
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Originally Posted by trashy View Post
it's just that the Megasquirt keeps asking for a value of 41.2 :(
tell the MS not to keep it at 41.2
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Old 12-29-2014, 09:22 AM   #4
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TPS is at ~1.5% in the log. You're not going to enter closed loop with that number. Recalibrate your TPS.
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Old 12-29-2014, 12:45 PM   #5
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TPS is at ~1.5% in the log. You're not going to enter closed loop with that number. Recalibrate your TPS.
Thanks Rev - now idles properly again
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Old 12-29-2014, 01:24 PM   #6
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This brings up something I was going to make a thread about.

Has anyone noticed issues with high mileage (150k+) TPS sensors? I soldered in an NB pigtail to Oregonmon's '90 wiring harness, which is PNP into one of Rev's MS3s, so I doubt it's wiring/MS3 related.

But we've not tested 3 sensors that go 5-20% negative when you just barely touch the throttle.

Owner of a local shop that specializes in Miatas says he's only replaced about 3 TPS sensors in the last 7 years. Our only thought is that the stock ECU doesn't really care how precise the TPS is. But when 2% keeps it at 1400rpm and 1% is back in CL idle, it's damn important.

This video is of me slowly moving the throttle wheel by hand, I turned it smoothly and only clockwise.

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Old 12-29-2014, 02:20 PM   #7
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you never want the TPS to be positioned so it's at the full stop.

readjust it on the TB so it's above the point where it acts like that.

re-zero and be a hero.
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Old 12-29-2014, 03:23 PM   #8
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Yes I've heard something about that before, what is this play you speak of? It just bolts on. There isn't a lot of room to move it either way.
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Old 12-29-2014, 03:50 PM   #9
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Thanks Rev - now idles properly again
Update:

Although the TPS varies by less than 0.5% when idling, I noticed that it seems to 'drift'. For example, TunerStudio was showing closed throttle at around 0% after re-calibrating, but nearly 2% once I had got back after a drive! After a few minutes it settled down to about 1%.

Sticky throttle cable perhaps?
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Old 12-29-2014, 05:34 PM   #10
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Oregonmons was doing that too. It would drift up from 0-5%.
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Old 12-30-2014, 09:03 AM   #11
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Yes I've heard something about that before, what is this play you speak of? It just bolts on. There isn't a lot of room to move it either way.
it bolts on, but you can position it relative to the shaft. The holes on the TPS are slotted for this very reason.

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PWM Idle Duty stuck at 41.2-18tps.jpg  
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