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The car is a 2002 Nissan Almera 1.8L ATX.

Normally the car idles in park about around 700 - 800 rpms and was showing a long term fuel trim of about -10%. Then one day I was sitting in park and all of sudden the rpms jumped to about 2500. I shut off the engine, and after restarting it, it was still idling high at about 1000 - 1100 rpms.

This has happened twice more since then, and the idle in park won't go below about 1000 rpm. The fuel trim is now about +7%. There are no trouble codes.

I took the car into a shop and they hooked it up to a four gas analyzer and it's lambda is perfect at 1.000, both at idle and held at 2500 rpm.

Maybe this could be a malfunctioning IAC or some other idle up device? How could I tell?

EDIT 21/7/17

One other thing which seemed odd was that Calculated Engine Load seemed pretty high. It was 33% when idling in park.

  • I would start by seeing whether the car has an idle air control (IAC) valve or electronic throttle control (you can't deduce based on the year as 2002 was around the time when electronic throttle control was being adopted). If the RPMs go up, it means it is getting too much air in addition to too much fuel. Just injecting more fuel won't cause RPMs to go up. – juhist Jul 10 '17 at 13:35
  • @juhist There is a throttle cable and an IAC. It may also have a separate idle up valve for the AC. – Robert S. Barnes Jul 10 '17 at 15:09
  • I guess the additional information means the engine is getting 33% of wide open throttle air. Seems high to me. Check the IAC and recheck possible vacuum leaks. – juhist Jul 21 '17 at 12:36
  • @juhist That's not what it means. TPS is just one variable used to calculate engine load. You can read more about it here: mechanics.stackexchange.com/a/17548/7132 – Robert S. Barnes Jul 21 '17 at 13:49
  • Isn't the load percentage related to airflow, exactly as I said? At least looks like it's airflow related based on that equation. Of course, it may be that you have a faulty sensor and thus the engine load is incorrectly calculated. But I guess that would mean you will also have an incorrect amount of fuel injected, meaning it actually may be getting more air than it should be. – juhist Jul 21 '17 at 13:56

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