Auxillary Air Regulator

My 84' 1.9 Camper shows signs of a faulty Auxillary Air Regulator. As per the Bently manual I did the hose pinch test (cold), no change in idle. Checked the voltage. Is it ok @ 14. + volts) ? With the connector off, the idle rocketed as the the ECU tried to correct. If there is no change in idle (cold or hot) is it stuck in the closed position or open ? and does that confirm the AAR needs replacement. What else should I check ?
Regards, Steve

Capt. Mike

Apparently it is staying in the open position since the hose pinch test when cold would cause RPM to drop. However, be sure you are "cold", i.e. test first thing after an overnight cool-down, so you are not testing in it's warm position inadvertently. Apparently it kicks out fairly quick since they test after only 5 minutes, which is not going to bring the engine to full operating temps.

I'd also check the temp sensors, especially #2 which activates the cold start system. They could be sending false signals to the ECU.

14v is pretty normal for a running engine as the alternator puts out 13.5v-14.5v, which in effect, becomes the system voltage.

I haven't got a real good handle on why the auxiliary air regulator's adding air to the system is better for cold starts. It seems backwards to the old carb choke that cut air down to enrich the fuel-air mixture. I can only assume the increased air-flow triggers the ECU to send additional fuel downstream. When I look at the wiring diagram, it would appear you could remove it and bench test by applying voltage to the controller and watching/listening for activation. Seem logical?

Update 2/1/01: Finally got a layman's explanation of the AAR adding air to the cold start system. The cold start is controlled by the Temp Sensor which tells the ECU to increase fuel -- apparently a lot. So the increased fuel requires additional air, which is supplied by the AAR. Thus you are getting not just an enriched solution by more fuel or less air (carb system), but a combination of both that takes into account the temperature of air & engine. Makes sense to you? Good, that's one of us.

[This message has been edited by Capt. Mike (edited 02-01-2001).]
Greetings, Thanks for the reply. Re-checked Aux. Air Regulator when really cold. Same results. Pulled AAR, its a bear, 10 mm hex nuts nearly impossible to get at. Replaced AAR and mounting bolts with 5mm allen. Also rechecked Temp. II sensor and it is within specs. Gas mileage went way up but still bogs/hesitates a little in lower RPMS, between shifts.
Thanks for your help. Steve

Capt. Mike

Now that you've got the AAR replaced, you may have to reset your FI. Bog down's cold often indicate excessive lean

Also check your idle switch. Since you have an idle and a partial throttle FI setting, perhaps it's tripping at the wrong time.

I bet it's fun to get to. The factory probably pulls the air-flow meter. Have you invested in a set of crows foot wrenches, yet? Sometimes they'll get where others fear to tread!
reetings again. Checked voltage on both switches, readings fluctuated wildly never reaching.5 volts but I suspect not the best contact between the leads. In a scan of the Bentleys only one reference to FI reset via O2 Sensor. If O2 was replaced before AAR should I disconnect again and is the correct way to reset the FI computer ?
Thanks again, Steve

Capt. Mike

I was refering to the Idle speed/CO reset per Bentley 24.29; the throttle valve per 24.33; and the full throttle enrichment switch, 24.34.

What you have to take into consideration is that during acceleration, the engine and FI go through a sequenced changeover of modes. If it doesn't get it right, there can be a hesitation or stumble. Too darn complicated for me, but the tests are at least pretty straight-forward. However, not everybody has a CO analyzer in the shop. There's where you need a friendly shop.

[This message has been edited by Capt. Mike (edited 02-01-2001).]

sandor feher

New member
I have just removed the aux. air regulator for a closer check. On the routine test the same results, pinching the hose did not change the rpm either at the cold stage or after running for about 5 min. There is batt. voltage at the connector.
The aux. valve in the closed position, cold, the gate valve has an opening of about 1/4".
It is the normal position for this gate valve to have a bleeder whole through it or it must be completly closed that one can not see through it?


New member
This thread is so old that I am aware the following will be of no help to the original member's question, but it may help someone in future. There seems to be come confusion about this component.
That aux air valve is actually a very simple way to increase fuel/air volume during cold starts (without any need to change position of the closed throttle valve as was done with carburetors.) A correct functioning aux valve will be fully open when the engine is cold (the actual opening is not round but angular, and only about 4 mm). No, the ECU does not "need the extra air because it is sending a rich signal to the injectors. That rich signal is from the ECU is INTENDED to provide a rich condition, and is unrelated to the aux air valve function.
Notice that the "extra air" passing through the open aux valve is arriving through a section of hose which joins the rubber intake boot. Therefore, it is air which will have ALREADY PASSED through the intake air sensor, thereby signalling the ECU that additional fuel is needed. All the aux valve does is bypass the throttle valve, with extra air needed to increase idle for the cold engine condition. It is extra air which has been metered and taken into account by the ECU, as it regulates the open time at the four injectors.
Whenever the engine is running the aux valve will receive system electrical voltage, and it is that current which heats a bimetalic inside the valve driving it slowly closed. The few I have tested take about three minutes from full open to move fully closed.
James Pate