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Old 02-20-2001, 12:24 AM   #1
Jason
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Member#: 105
Join Date: Jul 1999
Location: Fremont, CA 94538
Vehicle:
2000 Legacy GT Ltd
WHT

Question Unstable throttle % on S-AFC?

Finally get my S-AFC on my MY00 Legacy. Everything works good, except when the engine is on, the throttle % reading on S-AFC is unstable. I checked the sensor voltage reading. It looks like it's not getting stable power to get correct reading. The strange thing is, when the engine shuts off with ignition key on, the reading is 100% accurate.

I checked the ground wiring and rewired 2 ground wires and the wire for throttle %, but didn't change a thing.

I also checked the settings, In 5 out 5, cylinder 4, throttle arrow points northeast.

could it be a bad TPS sensor or just my bad wiring skill? I use walmart type splicers and swapped them when I rewired the 3 wires. Any input?

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Old 02-20-2001, 04:41 AM   #2
wac
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Join Date: Dec 1999
Chapter/Region: NESIC
Location: Lebanon, NH, USA
Vehicle:
2005 Outback 2.5 XT
Champagne Gold Opal

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Quote:
...when the engine shuts off with ignition key on, the reading is 100% accurate.
There's no such thing as 100% accurate. Repeatable maybe, but not accurate.

Back to the original question - it's normal to see noise on electrical lines. The noise is caused by spark plugs, distributors (both electronic and otherwise), electrical fans, pumps, radios, etc. Only worry if the TPS % readings drift by more than, say, 2% with the engine on. It's no wonder the TPS is stable with the engine off...

-WaC
Wayne
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Old 02-20-2001, 09:19 AM   #3
Jason
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It varies as much as 20%.
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Old 02-20-2001, 02:16 PM   #4
XTREME 2.5
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I have the same problem with my AFC. It varies all the time.
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Old 02-20-2001, 03:25 PM   #5
wac
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Location: Lebanon, NH, USA
Vehicle:
2005 Outback 2.5 XT
Champagne Gold Opal

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Then it sounds like you have a questionable ground connection for the S-AFC. Did you follow the instructions and connected the ground wires in the proper order? Also make sure that it is firmly connected to a good ground wire at the ECU, and not wrapped around just any bolt stud.

My TPS varies by 0.2% max during cruise. Try a highway run with the cruise control on, and see how much it varies on level sections.

-WaC
Wayne
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