TPS or Iac/Vacuum
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Junior Member
Joined: Jul 2008
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TPS or Iac/Vacuum
Hey Everyone,
Thanks for this great site.. saved me lots of time & $. This time I have a question that has been skirted around.. TPS failure or Iac / Vacuum leak.
My 97 4.6 F150 (400000 km/250000mi) is acting oddly around the same RPM's in all gears. I have replaced the TPS several years ago.
When I'm driving it will run fine unless I'm in a specific RPM range.. approx 1100-1250 (which is where it runs almost all the time - with my driving) - then it will pop up to about 1300-1350.. and then drop down again.. then pops up and drops down. Only ever in this range.
It will do this all day if I don't change the throttle position. There is no gear changing going on.. just a little dance around this spot. No other range causes this problem.
It also reacts this same way if I'm below this spot running fine & hit an incline causing a throttle increase while on cruise control.
Would this be a DEAD spot on the TPS or does the IAC / vacuum system make changes there that could cause a vacuum change specifically
Thanks again for a great site,
Thanks for this great site.. saved me lots of time & $. This time I have a question that has been skirted around.. TPS failure or Iac / Vacuum leak.
My 97 4.6 F150 (400000 km/250000mi) is acting oddly around the same RPM's in all gears. I have replaced the TPS several years ago.
When I'm driving it will run fine unless I'm in a specific RPM range.. approx 1100-1250 (which is where it runs almost all the time - with my driving) - then it will pop up to about 1300-1350.. and then drop down again.. then pops up and drops down. Only ever in this range.
It will do this all day if I don't change the throttle position. There is no gear changing going on.. just a little dance around this spot. No other range causes this problem.
It also reacts this same way if I'm below this spot running fine & hit an incline causing a throttle increase while on cruise control.
Would this be a DEAD spot on the TPS or does the IAC / vacuum system make changes there that could cause a vacuum change specifically
Thanks again for a great site,
Member
Joined: Aug 2008
Posts: 41
Likes: 0
This is a mass air flow engine management system...correct?
This sounds like the infamous "surging under a light to moderate cruise" which is caused by a lean condition. The computer gets just outside of it's window of adjustment due to the lean condition then it tries to compensate somehow to keep the motor running and the result is a surge.
I am not saying that this IS the case in your situation, but based on what you describe it is definetly a possibility.
This sounds like the infamous "surging under a light to moderate cruise" which is caused by a lean condition. The computer gets just outside of it's window of adjustment due to the lean condition then it tries to compensate somehow to keep the motor running and the result is a surge.
I am not saying that this IS the case in your situation, but based on what you describe it is definetly a possibility.