bizarre idle

[nkx]

the wagon (89 ea82t) has been idling strangely. idles ok off a cold start (a tad under 2000 rpm), then 5 mins or so after the car has warmed up the idle magically increases to ~2500 rpm. it holds that peak for about a minute, then drop offs suddenly to ~1000 rpm, and then build back up to 2500. it will continue to do this, with oscillations becoming more frequent as it runs. it will idle normally after about 10 mins.

 

im thinking the aav (or whatever its called, the thing on top of the thermostat housing) is borked. i really have no idea what else would cause something of this sort. if the aav is suspect, exactly how do i check it?

[barak181]

the wagon (89 ea82t) has been idling strangely. idles ok off a cold start (a tad under 2000 rpm), then 5 mins or so after the car has warmed up the idle magically increases to ~2500 rpm. it holds that peak for about a minute, then drop offs suddenly to ~1000 rpm, and then build back up to 2500. it will continue to do this, with oscillations becoming more frequent as it runs. it will idle normally after about 10 mins.

 

im thinking the aav (or whatever its called, the thing on top of the thermostat housing) is borked. i really have no idea what else would cause something of this sort. if the aav is suspect, exactly how do i check it?

 

Actually, I would check the intake manifold for a vacuum leak. What you're describing sounds exactly like a problem I had not too long ago and the culprit was the manifold gasket.

[Skip]

The AAV (Aux. Air Valve) is a controlled vacuum (air) leak.

As you suspect it controls the idle speed by varying this air leak.

 

The control valve is actuated by a bi-metal spring

heated by an element.

 

It sits on the t-stat so that if the electric heating element fails

the coolant temp will take over control.

The heating element it controlled by the ECU.

This connector is similar to the connector on the

FI coolant thermosensor.

 

First remove the connector and look for signs of corrosion.

 

Here is an easy way to remove these connectors

using two pieces of thin wire inserted under the clip.

 

Next check for battery voltage across the connector with the

engine running.

 

Check all the rubber lines to and from the AAV.

 

You might also want to check the thermosensor,

maybe the ECU doesn't know the engine is warmed up as

fast as it should.

[88RxTuner]

Check the CTS... if it's hanging and the ecm isnt seeing a warm engine, funny things happen. Check for the infamous corrosion problems associated with it. Check resistance on cold engine then warm engine, compare to specs (which I dont know off the top of my head..) Also possibly the AAV, check as SKIP advised. Possibly a vacuum leak, but that would tend to make it act funny all the time, not just for 10 minutes...

[nkx]

thanks for the replies, guys.

 

i will check the aav connector. last i checked, i didnt see any corrosion. skip, should i check for voltage when the engine is cold or hot?

 

i replaced the CTS last summer, so i dont think its suspect, unless the advanced auto pieces are known to be defective.

[Skip]

nk,

voltage should be present any time engine is running

.

 

You found a thermosensor at advanced, kewl, but I would use a OEM for this important part.

Sure you don't mean

dash gauge sender unit (called a thermometer in the FSM)

 

The thermosensor has the same type connector as the AAV and is burried deep

in the back pass side of the intake manifold.

 

For kickies, check the ground for the ECU and other dash components.

It is located under the pass side front intake manifold bolt.

 

I say this as the element in the AAV may also get it's ground from this point.

BTW the fuse for the AAV is number 12.

 

Hope this helps.

[nkx]

well the aav has voltage. i played with the idle screw, and noticed that it would stop the oscillation if i had it screwed in most of the way. it would still idle pretty high, though. puzzled, i shut the car off, and restarted it. then it was idling normally, just under 1k rpm.

 

would a dud cts really skew the idle that much?? and what is the small screw facing the firewall on the back of the throttle body for? i turned it and didnt see any result.

[86BRATMAN]

Ok, I've been around a few cars that will do this if there is air bubbles in the coolant system. May want to bleed it for a few minutes and see if that helps.

[daeron]

and what is the small screw facing the firewall on the back of the throttle body for? i turned it and didnt see any result.

 

 

He isn't talking about the Idle Stop screw, is he????? that screw should have a white paint mark on it from the factory, and should never be touched, from what I understand..... I cant visualize where it is, though...

[nkx]

Ok, I've been around a few cars that will do this if there is air bubbles in the coolant system. May want to bleed it for a few minutes and see if that helps.

 

how would i go about this? remove the rad cap and let the car run for a few mins?

[beataru]

Actually, I would check the intake manifold for a vacuum leak. What you're describing sounds exactly like a problem I had not too long ago and the culprit was the manifold gasket.

yeah +1 on that, Mine is doing the exact same thing, except when i hit boost, it goes super rich and boggs, Somewhere I have a metered air leak.