new jasper motor repair shop install,new o2 senser,thermostate,fuel filter,and cluch. has a header cold air intake. already checked 4 vacume leaks. computer code said something about air temp and it wasnt the senser. took it back to shop yesterday mech ajusted timing. then told me he got it to idle fine inside the garage but when he took it for a test drive (its realy cold here) and said it started to idle high again. he told me its because of the cold air intake. i had the intake on the old motor with no problems drove it in the cold, warm and in between. any input would be great thanx

Any changes to your exhaust??
Low exhaust temp at the 02 sensor will tell the computor to add fuel .
I believe the 02 sensor needs 650 deg to register correctly...exhaust changes could keep this from reaching it's optimal working temp......like removing the cat

every things the same as it was with old motor. just new jasper swap. again it ran fine before the old one crapped out.

Any changes to your exhaust??
Low exhaust temp at the 02 sensor will tell the computor to add fuel .
I believe the 02 sensor needs 650 deg to register correctly...exhaust changes could keep this from reaching it's optimal working temp......like removing the cat

An O2 sensor doesn't read temp. If it reads lean it will add fuel. It does need to heat up to work efficiently and I don't believe exhaust chahges should affect it. I also believe that that should have a heated O2. Should have 2 or more wires. If the coolant sensor for the computer is ready to cool it will want to idle higher. Also have the tps checked and check and clean the idle air control.

Quote from: DistantSmoke on January 26, 2008, 08:30:18 AM

Any changes to your exhaust??
Low exhaust temp at the 02 sensor will tell the computor to add fuel .
I believe the 02 sensor needs 650 deg to register correctly...exhaust changes could keep this from reaching it's optimal working temp......like removing the cat

An O2 sensor doesn't read temp. If it reads lean it will add fuel. It does need to heat up to work efficiently and I don't believe exhaust chahges should affect it. I also believe that that should have a heated O2. Should have 2 or more wires. If the coolant sensor for the computer is ready to cool it will want to idle higher. Also have the tps checked and check and clean the idle air control.

Sorry that sentence should read" If the coolant sensor is reading too cool it will want to idle higher"

Quote from: DistantSmoke on January 26, 2008, 08:30:18 AM

Any changes to your exhaust??
Low exhaust temp at the 02 sensor will tell the computor to add fuel .
I believe the 02 sensor needs 650 deg to register correctly...exhaust changes could keep this from reaching it's optimal working temp......like removing the cat

An O2 sensor doesn't read temp. If it reads lean it will add fuel. It does need to heat up to work efficiently and I don't believe exhaust chahges should affect it. I also believe that that should have a heated O2. Should have 2 or more wires. If the coolant sensor for the computer is ready to cool it will want to idle higher. Also have the tps checked and check and clean the idle air control.

I don't mind being corrected as long as the person doing the correcting actually knows what they are talking about.
  If one removes their catalitic converter in hopes of creating more power by increasing exhaust flow they actually reduce the temperature of the exhaust system and their engines ability to run efficiently and cause more problems that result in a loss of power.

  The sensor does not begin to generate it's full output until it
     reaches about 600 degrees F.  Prior to this time the sensor is
     not conductive.  It is as if the circuit between the sensor and
     computer is not complete.  The mid point is about 0.45 volts.
     This is neither rich nor lean.  A fully warm O2 sensor *will not
     spend any time at 0.45 volts*.  In many cars, the computer sends
     out a bias voltage of 0.45 through the O2 sensor wire.  If the
     sensor is not warm, or if the circuit is not complete, the computer
     picks up a steady 0.45 volts.  Since the computer knows this is
     an "illegal" value, it judges the sensor to not be ready.  It
     remains in open loop operation, and uses all sensors except the
     O2 to determine fuel delivery.  Any time an engine is operated
     in open loop, it runs somewhat rich and makes more exhaust
     emissions.  This translates into lost power, poor fuel economy
     and air pollution.

This is just a little info to help you understand how an 02 sensor actually works.

Although the poster did not do any exhaust changes I would still suggest that the 02 sensor is in limbo and that is why the engine raises idle and then drops into loop....perhaps a cleaning of the 02 sensor would solve this problem. If the wrong gasket material was used in the new engine install the 02 sensor may have been damaged.
 Just trying to help the poster

Thank you for correcting nothing. I do understand how an O2 sensor works. My point was it doesn't read exhaust temp like you made it sound like it does. And having a convertor or not shouldn't make a big difference if the convertor has no blockage. That should have a heated O2 should it not? Also an faulty O2 should bring on an engine light and would make it run fatter. It controls fuel not air! So I would look at things that can control idle speed like idle air control or tps values, vacuum leaks, etc. Also a vehicle doesn't only use O2 sensor values to go into closed loop. It also uses coolant temp. And since we are correcting each other when the computer is in open loop, it decides when to take the reading from the O2 sensor. When it is in open loop it uses a predetermined set of values from the factory. Otherwise LIMP mode.