For those that are following my saga, I put the Holley throttle body back on the car today and bought a longer screw so I can turn the idle out farther. I start the car and it idles pretty well. The IAC counts are pegged at 160. After it starts to warm up, the IAC counts slowly begin to come down, then they come down progressively faster and faster until they hit 0 at around 170*. Then they just stay put at 0. I've tried setting the minimum idle a couple times and it just doesn't want to play nice.

 

I have a 52 mm BBK. Had the smae problem, turned out I had to return it for machining. The wer certain passages left out. If you original works then you know it it Holley. Talk to holley!!

 

I think my original did the same thing. I didn't babysit my original, but I do recall that the counts were at 160 as it warmed up. Once it was warm I saw that it was at 30-34. A little while later I went back to it and the counts were at 0, but I figured it was because the communication between my scan tool & the ECM hiccupped, but maybe not. I might have to put the stock one back on and follow its behavior a little closer.

 

0 means the IAC cant operate anymore. Get the car hot and with the fans off. Check the reading. If no good disconnect the red and black pigtail connector by the battery. back the screw out a tad. Plug the connecter back in and start it back up. Back off on the screw till you hit about 15 in park. it'll idle real nice.

 

I don't have park. It's a 5 speed. I've been screwing with the IAC for 2 weeks and I can't make it behave. I started this whole fiasco by trying to set the minimum air and the TPS, but the IAC won't play nice. I set the minimum air, then when I plug the IAC back in it just sits there pegged at 160 counts.

 

I used to do it that way with disconnecting the IAC connector and the grounding out but I found that not to be a very good way of doing it.

 

This thread is a bit old now, but someone may still be looking for the answer. Patrick's comment about BBK's missing passages is also what's wrong with the Holley TB. The IAC passage on the Holley unit is a hole that dead ends into the TPI plenum. They didn't connect the IAC passage to the butterfly passages. I took out my dremel and made my own passages. It's not the prettiest work, but it's effective and it’s the way the stock unit connects the passages. I’m attaching a fuzzy poor quality picture (sorry its so bad) to show what I did. Basically, look at the plenum side of the stock TB and the Holley TB and you’ll see where they went wrong. A working IAC does wonders for cold start idle.

Also, anyone who has a custom TB top plate should know that it won't fit on the Holley TB. They offset their screw holes just enough to ensure you'll have to keep the Holley name plate on top of it.

Joe
92 Z28

 

That's because you have a 92 and you bought the old-style throttle body. I have an 85, so my plenum has the hole that directly lines up with the hole on the holley.

Now you've got me wondering about the plate holes too. I could have sworn I pulled the holley plate off and tried it with sucess on the stock throttle body. I guess I'll have to check that out next time I get a chance.

 

My Summit invoice says I have model 112-506. Summit doesn't seem to carry it anymore, but Jegs and Thunder Racing do. They both list it as the 89-92 TPI, 52mm model, so I should have the one advertised for my application. Is the model # ground into the TB anywhere?

I'm attaching two pictures to show the difference between the stock and the Holley top plate. One is a picture with a stock style Z28 plate over the Holley plate. I aligned the middle two holes. You can see the Holley plate sticking out below the bottom of the stock plate, and the Z28 plate would stick out past the top of the Holley plate. They actually line up better if the stock plate is upside down. The outside holes don't line up when the middle holes do, the Holley spacing is narrower than stock.

For the second picture, I placed both plates on graph paper with 1/8" squares and marker where the holes fall. The red marks the Holley holes and the green marks the stock holes. You can see by the graph paper lines that all of the Holley holes fall on a straight line, the stock holes don't.

So as long as I was shipped the model I ordered, Holley doesn't build them correctly and the top plate doesn't fit. There's a whole long list of other problems with the unit, like the TPS sensor cut out and screw holes are wrong, the throttle cable pin is too large for the plastic clip on the cable, and the throttle plates hit the inside of the TB well before a reasonably low TPS voltage can be reached. Basically, Holley blew it.

 

It seems you can't attach 2 images to a post, so here's the second image.

 

They did just fine on mine.

I got my TPS sensor to fit in 10 seconds by just filing it down 1/8". The different thread size irritated me, but if Holley had simply included the proper length screws instead of those short ones, it would have been a non issue. My throttle cable attached perfectly, and the throttle blades fit perfectly in the bore. Movement is very smooth. It sounds like you just got a bad one.