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Discussion Starter #1
I installed the HKS 264 cams on my T-64 car. With the "18B" VPC PROM (the one for big single/big twins and stock cams) in the VPC, the engine idled at the correct RPM (approximately 700) but with an A/F ratio of approximately 12.8:1 (should be approximately 14.7:1). BTW, I'm measuring the A/F ratio
with a wideband, so it's accurate.

I switched to the "18C" VPC PROM (the one for big single/big twins and upgraded cams). Now the idle A/F is just right at 14.7:1, but the car idles at approximately 500 RPM.

Is there any way to adjust (raise) the idle speed without using the set screws on the throttle linkage -- like an adjustment to the IAC or something? I've put feeler gauges under those set screws to temporarily mimic an adjustment to those screws, but it just doesn't seem to act right -- idle speed isn't consistent and solid.

The best way I've found to bring the idle up is to pull a small vacuum hose off the intake plenum. If I do that, it idles perfectly and at the right speed, (but that's not the sort of long-term fix I'd like to employ LOL). That makes me think that the IAC valve needs to be allowing a little more air into the intake. I COULD rig a manual valve (just like a manual boost controller) on a hose from the intake (probably need to install a dedicated hose in the IAC channel on the inside of the intake plenum) with a small air filter on it and a check valve to keep it from leaking boost. I could then control the idle speed with that manual valve. <shrug> But, I'm hoping there's a better, easier way. Any of you have experience with this?

Steve
 

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What about a small hole drilled through the throttle plate? An old hotrod trick used with long duration cams.

Start small and work your way up.

Kind of hard to change your mind after you do it, though :).
 

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Discussion Starter #3
Theoretically, that should work, but I'd rather do the bleed-valve thing I mentioned. That way I'd be able to reverse it if I changed cams or something where I didn't need the extra air.
 

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Boost Junkie said:
Theoretically, that should work, but I'd rather do the bleed-valve thing I mentioned. That way I'd be able to reverse it if I changed cams or something where I didn't need the extra air.

You can use the two hoses that the power steering uses to bump the idle up. Just connect them together.


Lar
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As I understand it, the PS computer lets air around those two hoses when the PS pump puts a large load on the motor. That way it lets air by the throttle plate so it doesn't stall at idle.
 
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