I am chasing down an on again, off again cell 16 split BLM. One minute they are close +/- 3 points then they go huge split for no apparant reason.

The car normally idles perfect with 35-45 points on the IAC. I also have the bypass hole drilled in the idle circuit path because without it, the IAC points were too high. Also there are no obvious vacuum or exhaust leaks to be found.

I am focusing on the idle circuit of my BBK 58mm TB which is much different than the idle circuit on the OEM TB.

My BBK 58mm TB allows the idle air stream to enter the intake at the port large port openings (behind the butterflies) because of a pair of machined paths (yellow arrows) not found on the stocker:


Again an OEM TB does not have these machined paths and forces all idle air into the small bottom hole on the front of the LT1 intake which is then evenly distributed to all 8 ports through the paths inside the intake.

Why is this not the case for an aftermarket 58mm TB?

I have googled myself silly and have found that many with this TB have the same problem and they blamed the NON OEM idle circuit. I also ran across this writeup where the guy installed tubing to force the aftermarket TB to use the OEM idle circuit:
http://www.noid.org/~lj/PCM%20Tutorial/SplitBLMinfo.htm

I have never found a reason for the difference in the idle circuits on these aftermarket 58mm TB's.

Anyone have any success modding their idle circuit back to stock like to address split BLMs?

Comments?

 

My TPIS 58MM has the same short circuit paths. I blocked them with silcone and my BLMs are almost perfect. I have a big-*** cam also.

Very easy mod.

 

Its good to hear that you were met with positive results after plugging the paths. But I wonder why they are they there in the first place?