What are the two little holes for behind the throttle bores on tpi pleniums? I have two different pleniums, an 86 and an 89 and both have the holes filled with carbon, what are they for, I'm guessing egr due to the amount of carbon.. what is a good way to clean them out? Also what is the small triangular hole for behind the throttle body on my 86 plenium and why doesnt my 89 have it?

 

the 2 holes behind the throttle blades are for egr. you can clean them with a can or 2 of carb cleaner although prob not a good idea to do while its on the car. as for the single hole im not to sure.

 

EGR only on the later cars and EGR with cold start injector on earlier TPI's. The triangular hole is for the Idle Air Control on the earlier TPI. On the 89 and later they changed the throttle body design and they did not need the triangular hole.

 

I'm planning on using the 86 plenium on my 89, can I use the 89 TB with it or do I need to use the 86 TB? Will this cause any problems?

 

I think they have to match or the IAC won't work. One swap works the other doesn't but I don't remember which.

 

I believe the 86 plenum has the triangle. It can be used with any throttle body.

 

I hope you're right! I'm gonna find out..