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Possible IAC Problem and error codes.

Tiny
RAZGRIZPR
  • MEMBER
  • 1997 MITSUBISHI MIRAGE
  • 171,000 MILES
Hi!

I have a 97 Mirage 1.5L Auto. The problem with it is that whenever I'm accelerating and release the gas pedal for a few seconds and then accelerate again, the tranny tries to change gears suddenly and abruptly a couple of times. By that I mean that it changes back and forth in a couple of seconds and this usually from 2nd to 3rd gear.

This situation started when I changed the Idle Air Controller. My car had a 3000gt throttle and IAC, it has been installed for 8 months already. I decided to put the original IAC back and that's when the problem stated above began, it was worse than described. I then dicided to put the car in it's original state so I installed the original throttle with its IAC. The problem remained, so I swap the IAC again for the 3000gt IAC, the car runs much better and the problem above is minimal but it still happens.

Could this mean that both IAC are damaged? Why it started to happen as soon I swapped them?

I also want to add that I have the following codes:

P0120 - Throttle/Pedal position sensor
Sensor A CKT Malfunction

P0170 - Fuel Trim
Malfunction Bank 1


Can someone explain to me what is the fuel trim and where is it located?
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Thursday, December 29th, 2011 AT 2:45 PM

10 Replies

Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Try replacing your gas pedal, that is the code 120 it may straighten out. The fuel trim may be a vacuum leak like a line left off or someting similar. It may all be coincidental with teh iac. If it continues after the gas pedal change have a trans guy run a scan on it as ther may be something else in the trans screwing up.
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Thursday, December 29th, 2011 AT 3:28 PM
Tiny
RAZGRIZPR
  • MEMBER
  • 5 POSTS
Alright, I will check that out. Does it have to be replace or can it be adjusted?

I find it weird to happend right after changing the IAC especially since it reduced the problem dramatically after replacing the IAC. I never thought of the pedal just the TPS.
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Thursday, December 29th, 2011 AT 4:19 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
It has to be replaced becasue it's a rheostat device and there is no adjustment. It's an assembly and you'll need to erase the codes after you do this.
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Thursday, December 29th, 2011 AT 5:37 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
The TPS is attached to the throttle body and it can go out of adjustment if it had been tampered with.

You would need a DVOM and a feeler gauge to adjust the TPS.

The TPS affects gear shifting as the signal from the TPS is channeled to the tTCM and sionce you have the TPS trouble code, you need to get it resolved.
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Thursday, December 29th, 2011 AT 6:17 PM
Tiny
RAZGRIZPR
  • MEMBER
  • 5 POSTS
I adjusted the TPS and the car is working fine, I just have to tune it but at least the problem has disappeared. Will test it for a few more days and see how it behaves.

What I can't still understand is the fuel trim. What exactly is that and how can I fix it?

Thank you hmac300 and KHLow2008!
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Friday, December 30th, 2011 AT 11:53 AM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Go to this link and understand how it works: http://www.youtube.com/watch?v=mzsOY_AhgY4
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Friday, December 30th, 2011 AT 12:15 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
Any error with the TPS can affect the fuel trim so you need not worry about that for now.
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Friday, December 30th, 2011 AT 3:36 PM
Tiny
RAZGRIZPR
  • MEMBER
  • 5 POSTS
Sorry for such a late reply. I was away because of the holidays. Thank you so much for your help and the video.

I have been looking for anything that could explain the correct position for the TPS. Do you guys now any?

Thank you!
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Friday, January 6th, 2012 AT 1:10 AM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
TPÂ SENSORÂ ADJUSTMENT

NOTE: Ensure basic idle speed is set to specification before adjusting TP sensor. See BASIC IDLE SPEED under IDLE SPEED & MIXTURE. Perform all adjustments
with engine at normal operating temperature,  front wheels in straight ahead position,  cooling fan and all accessories off,  and transmission in Park or Neutral.

1. Disconnect TP sensor connector. Using jumper wires,  connect an external ohmmeter between TP sensor terminals No. 3 and 4. Insert a feeler gauge with a thickness ofÂ.177" (.45 mm) between fixed SAS
(throttle stop screw) and throttle lever.
2. Loosen TP sensor mounting screws and rotate TP sensor fully counterclockwise. Ensure there is continuity between terminals No. 3 and 4. Rotate TP sensor clockwise until there is no continuity and tighten
screws. Install Test Harness (MB991348) between TP sensor and harness connector.
3. Turn ignition on. Using external voltmeter,  measure TP sensor output voltage between terminals No. 2 and 4. If voltage is notÂ.4 1.0 volt,  check harness and sensor. See DTC P0120 in TESTS W/CODES  1.5L
article.
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Friday, January 6th, 2012 AT 1:20 AM
Tiny
RAZGRIZPR
  • MEMBER
  • 5 POSTS
I want to thank to each one of you for your assistance and help.
I still have some of the issues but I'm taking the care to a shop so the TPS can be tuned correctly and check any other issues. Hopefully it will be fixed after that.
Thanks!
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Tuesday, February 7th, 2012 AT 11:24 PM

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