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03-Feb-07 Relocating the Idle Air Controller Part 1

The Magic Hat



I'm feeling pretty optimistic about getting all the little bugs worked out of the car by spring. I wrote (in frustration) a while ago about all the little things that still needed to be addressed. The largest issues being that the transmission was always engaged and that the engine had a sporadic idle.

I assumed that the transmission issue was caused by the torque converter but that was not entirely the case. When I told the guys at Jay Egge Transmission that the engine would kill when I put it in gear unless the idle was up around 1400 RPM, it raised a few eyebrows. Sure enough, the new pump was defective. It had a bleed back issue that caused the converter to stay engaged at idle. It checked out fine on the transmission dyno because it was running and the output shaft was never held from turning as it would be when you're sitting in gear with your foot on the brake. So, we can add that pump to the list of defective new parts that could only happen to me.

Even though I haven't driven the car with the latest rebuilt transmission and new torque converter, I KNOW it's going to work – I have faith that it's fixed. That just leaves me with the engine idle dilemma. The engine always surges between 900 and 1500 RPM at idle. It's not an even surge either – it's all over the place.

I've shared how I used to be into Corvairs pretty heavy at one point in my life. Corvairs inherently have the same issue when they get a bunch of miles on them. It's because the aluminum carburetor castings wear from the butterfly cross shafts. The shafts themselves also wear and eventually you can rattle the shafts in the hole. This causes air to leak into the carb and the engine to surge sporadically at idle.

There's a fix for the Corvair carburetor shaft issue – you simply re-bore the holes and machine larger shafts that fit snug but don't bind – like new but oversized. The issue I was having with Project33 was so similar but with electronic fuel injection and all new parts, I was assuming it was something with the idle air control or something else electrical.
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I've been toying with the idea of moving the idle air controller (IAC) from behind the injector hat [ 2/2/05 article "What a CAD"] to a more centrally located and better concealed location – inside the injector hat. The passenger side hole of the injector hat is blocked off inside the hat, so my idea was to make use of the unused barrel by opening the bottom (for airflow) and placing a bulkhead in the block-off plate for the IAC.
ImageI removed the injector hat and placed it upside down on a soft cloth to have a better look. I was amazed at what I found! The aluminum block-off plate is welded in several places and then sealed with JB-Weld. The JB-Weld had given way in several places and the entire bottom edge (top if the scoop is right side up) was cracked. I could slip a sheet of paper through the cracks around the plate!

Now normally this would be trying to draw air from a closed area at idle but when the butterflies were sticking (closed) I removed a bunch of material from the edge of the unused butterfly, since it didn't have to make a seal when closed. You guessed it – there was enough air leakage going on there to make the engine idle like crap.
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You can see the areas where I chipped out the JB-Weld and also the crack along the bottom of the block-off plate in the photo above.