Help me understand the AAR please.

[siteunseen]

Wick Humble's book, page 194, talks about a recall for '78s "High-Idle Problems". I could scan it for you later today if it's something you haven't read. Mostly the PCV system re-routing and a newer PCV valve off a '79, cleaning the throttle plate and changing the return spring.

[TomoHawk]

Something seems to be funny with my AAR, probably. The engine doesn't idle-down after a minute, and after driving for a short time, the idle is up to 1500 in neutral. I even plugged the AAR tube into intake manifold.

[Captain Obvious]

So what happened when you plugged the AAR inlet into the manifold? Did the idle drop to where it's supposed to be once the engine is warm?

My original AAR was intermittent. Tricky part was that it always tested fine on the bench when cold, but went "open" once up to full temp.

So I know you already replaced your AAR with new and I would hope (assume?) that the new AAR does not have an internal problem. It might, but let's hope not, so...

How about the 40 year old cracked, crusty wiring and loose, corroded connectors leading TO the AAR? Maybe there's an intermittent connection somewhere?

[TomoHawk]

I used a little strip of aluminum from a pop can (they're useful little, and you can cut them up with hobby scissors.) I loosened the screws where the air goes into the throttle, slipped the strip in, and tightened. The cardboard strip I tried before had a hole in it. I used a knife to trim off most the exposed part of the aluminum strip.

Now the idle is very low when you start the engine, as you'd expect) so I give it a minute to warm up by stepping on the gas pedal a little.

You'd think they would add a thing to do that for you! Something like a timed valve to increase the idle for about a minute?

If only you could get a thermotime switch that closed after about a minute when the coolant is 'cool'. You could add a solenoid valve, and take off the AAR.

[EuroDat]

Now the idle is very low when you start the engine, as you'd expect) so I give it a minute to warm up by stepping on the gas pedal a little.

How is the idle now when it warms up?

[TomoHawk]

After about a minute, when the engine gets warm, the idle is low (about 1100-1200) and smooth.

My first idea to replace the AAR with an electric valve would be to use the Thermotime switch to start a timing device that operates a very small solenoid valve (or similar) to provide the fast idle air for about a minute. The air would use 1/4 inch hose (about a 1/8 inch NPT valve) or have that large of a valve opening (about 5mm diameter.)

I think it is possible that the Thermotime switch closes even when the coolant is hot, because it's in an area of high airflow, so a more reliable temperature sensor/switch is desirable, probably one that is considerably enclosed within the thermostat box, in the same place where the coolant bypass orifice for the AAR is!. One less hose cluttering the engine head area...

Edited June 24, 2013 by TomoHawk

[EuroDat]

My first idea to replace the AAR with an electric valve would be to use the Thermotime switch to start a timing device that operates a very small solenoid valve (or similar) to provide the fast idle air for about a minute. The air would use 1/4 inch hose (about a 1/8 inch NPT valve) or have that large of a valve opening (about 5mm diameter.)

Or you could go retro and fit a 240Z choke handle in the console to operate a manual bypass valve

[TomoHawk]

That would spoil all the fun of tinkering with the L-Jetronic wiring :laugh: