2.5 L Engine rpm modulation

[Guest pelagic30]

90 Legacy with 2.5 L, the book says the idle cannot be adjusted mechanically, so what sensor(s) do I start looking at. When sitting in neutral at idle, the engine rpm falls down to about 200-300 then the ECU realizes that the engine is running way too slow and kicks it up to 1000 rpm, then it falls back again, cycling up and down once per second. The car runs great otherwise and this is not really a problem (yet?) but I would like to fix this if it is a sign of future problems. The car has 83000 miles, as far as I know it has all the original engine parts / sensors.

 

Thanks

[Guest rcoaster]

It could be your Idle Air Control (IAC) valve, or a loose vaccuum hose somewhere. Check for vaccuum leaks. Also, there might be deposits on your throttle body as well, that might affect the idle speed.

 

BTW, how did you get a 1990 Legacy with a 2.5? I thought those didnt' come out in North America until 1995! You must mean the 2.2L.

 

-RCoaster

[Guest Legacy777]

You have a 2.2 liter in your 1990 legacy.

 

The IAC valve is most likely sticking. It is located below the PCV valve. There was a procedure around here some where on how to clean it. Anyway, the jist of it is, you need to remove the top electro magnet portion of the sensor. Before doing this, make sure you scribe the orientation of the top controller portion to the body, so you get it aligned exactly how it was before. With that off, try and move the IAC valve. It should move freely and be smooth. If it doesn't, remove the hose that connects to the intake arm that's connected to the IAC valve. Spray some brake cleaner in there and work the IAC valve back and forth until things are moving freely and smooth.

 

The above is assuming you have an AT. If you have a MT, they use a different valve, and from a buddy's experience trying to clean his....it didn't work to good.

 

oh yeah....do check for vacuum leaks as well before you tear into cleaning the IAC valve.

[Guest pelagic30]

Ok 2.2L, I was looking at the wrong VIN codes.

 

Thanks for the great advice ! I think a vacuum leak is a distict possibility as I noticed some mouse turds around the engine compartment.

 

I didn't think it was possible to be happier owning a Sooba Roo, but finding this forum certainly has.

 

Thanks again,

 

Keith

 

88 DL Wagon (same old 1.8L)

90 L AWD Wagon (now with 2.2L engine)

90 L 2WD Wagon (also now with 2.2L engine)