I have a 1990 TII that I had in storage for 7 or so years, and it has had an idle surging problem since being removed.

I took the BAC valve off to check it (tested 11 ohms, should be good) but I was surprised when I looked at the UIM. Is this port factory?

<a href="http://s222.photobucket.com/albums/dd66/crackattak/?action=view&amp;current=BAC.jpg" target="_blank"><img src="http://i222.photobucket.com/albums/dd66/crackattak/BAC.jpg" border="0" alt="Photobucket"></a>

 

Yes. the little port on the left part of the mating surface is where additional the bypass air flows through, independent of the commanded duty cycle for the BAC valve. That airflow is controlled by the air adjusting screw on the BAC valve. The n/a engines have an equivalent screw on the top of the intake manifold. The FD throttlebody and manifold have the equivalent screw underneath the TB elbow. Most engines with idle air control valves have some kind of bypass air adjustment screw.

The holes in the middle are holes in the primary runners to allow the bypass air from the valve to flow into the primary ports.

 

The reason why I ask is that the previous owner (10 years ago) had the engine rebuilt and I have found numerous spots where who ever did it screwed or rushed something: wiring harness, gaskets, hoses, bolts/nuts, etc.

The holes look symmetrical, but those points are very sharp and the internal edges are rough, something about it just looks makeshift to me.

Am I a hypochondriac?

 

yes. my s5 JDM manifold looks a lot like that when you pull the BAC valve off. the difference is that it doesn't have the little port for the air bypass screw. my USDM s4 T2 manifold also looked similar, except that the holes in the middle (the one you are concerned about) are smaller.

 

Alright, thanks.

The valve seems to be pretty clean with the right resistance, I can hear it clicking away with each idle surge.

 

if you havent already check the TPS adjustment, and then reset the idle speed per the FSM.

the way the S5 ecu controls idle speed, if its to high, it will surge.

 

Yeah, well I made my own test light per the instructions on FC3s and I must be doing something wrong. I could not get either light to stay illuminated, they would just blink once when each plunger was activated. I am not sure if the blink means the TPS is shot or my light is garbage, but I don't see how the simple tester could be bad. Perhaps I should buy one from Banzai, even thought I'll feel like an idiot for buying a 25 pair of led's.

So I have it temporarily adjusted precisely (I guess as precise as possible with what I am working with) to the point where the narrow blinks, then backed it off a hair.