• Tiny
  • creature
  • 1991 Toyota MR2

Engine Performance problem
1991 Toyota MR2 4 cyl Two Wheel Drive Manual 134000 miles

I have replaced the head on the 3sgte engine with a u.S. (California ) head to pass smog. I pulled the engine to do so. Everything was marked and I took pictures of everything possable through the process to be sure everything went back were I found it. The vehicle ran very well before I did this with the japanese engine I had installed about a year ago. I have checked and double checked all electrical routing and connections and vacuum connections. Everything appears to be correct. At first the vehicle would not start, then I replaced the ignition relay and it started right up. The issue I am having now is: When I start the vehicle it runs. It does not idle steady. It fluctuates very steadily from 1000rpm to 2000rpm and back down again. Right off the bat I thought it was a vacuum leak. Checked all connections and all are well. Advancing the timing or retarding it does nothing to affect idle. Unplugging vacuum lines does nothing to affect idle. Adjusting the copper air adjustment screw on top of the throttle body does nothing either. Neither does unplugging the isc valve on the side of the throttle body. The isc requires an ohm reading between 17.7-23.9 and both the rsc to +b side is recieving 21.8 and the rso side are receiving 21.7 ohms. Reving the throttle control does nothing to affect idle, the only differance their is hearing the intake open. Pulling either the mass air flow meter control @ the intake or disconnecting the throttle position sensor makes a huge differance and so does pulling the spark plug caps. I am recieving diagnostic codes 24: intake air temp signal, 31: air flow meter signal ( vacuum sensor signal ), and 41: throttle position sensor signal. Please help, I am completely stuck.

Tuesday, March 11th, 2008 AT 9:05 PM

1 Answer

  • Tiny
  • creature
  • Member

After all the searching I figured it out. I set the throttle possition sensor incorrectly when I loaded the sensor it was holding the throttle valve open. I took it off and reset it correctly. I learned that the TPS, when loaded should not apply any pressure to the throttle valve, but it must still be spring loaded. When the tps is loaded correctly it should have a very faint pressure that almost moves like thier is not pressure. But when you let go it should softly kick back showing that it is under slight pressure. On the side of the tps were the screws hold its adjustment you should see spot were it looks like screws have been their before. It is best to set the sensor back to that position. If you are replacing the sensor. Refer to the old sensors wear marks.

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Tuesday, March 11th, 2008 AT 10:50 PM

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