Yes, another idle question. With the stock throttle body the car would idle properly. With the 52mm the minimum idle screw is turned all the way in and it barely idles around 350-400rpm. I've followed the Tech article on setting minimum idle and adjusting the IAC and TPS. When it's cold it will not idle, warmed up it idles but is around 400-500 in drive and maybe 500rpm in Park. The car runs fine otherwise. Maybe there is a problem with the throttle body? Has anyone else had a problem with the Holley? Oh yeah, I replaced the IAC (didn't change anything) and the TPS sweeps cleanly from .54 up to 4.67. Thanks.

 

Might try raising the TPS voltage a little, but without a change in the PROM it will never be perfect. You are flowing more air now you need more fuel.

 

You're not flowing more air unless the engine tries to suck more. You sure aren't flowing more at idle!

I have/had the same problem with my 52mm throttle body. I needed to install a screw that was longer than what came with it in order to get a 750rpm idle. However, I'm still having a ton of problems with my idle because for whatever reason, my IAC circuit seems to be a mess even though I replaced the ECM (twice), IAC (twice), repinned the connector, tested the wiring multiple times, and set the idle air procedure more times than I can count.

I find it very interresting that you're having the same problem. Maybe it's not just me after all.

 

OK you are right. I had to think about it but you are correct

 

So did replacing it with a longer screw fix your issue? I am having a simliar issue with a holley 52mm.

 

Log some data and see where your IAC counts are.... You will want 10-20 counts at idle.... The IAC will tell you if your minimum air setting is right or not. Get the IAC counts down and set the TPS and you are done.

 

I can't get my IAC counts to stay put. They start peaked out, then slowly drift to zero, which is where they stay.

87iroc350, replacing the screw didn't "fix" the problem, but it at least allowed me to set my idle at the desired RPM... but due to my non-functioning IAC situation, the screw is turned out a lot farther than it should be to achieve that idle rpm.

 

I was thinking also that a temporary fix might be to get a longer screw than set the TPS accordingly. In the tech section it says over 4.0 volts is fine at WOT. Mine where it stands now is at 4.67, so I'm assuming it will go down some but still remain above 4. Is there really a max and a min of voltage at WOT that you should have? :shrug:

 

Even with the longer screw, you can set your TPS to work fine. The dual slotted screw holes allow you to set your WOT and idle voltages somewhat independantly. Screw around with just moving one or the other until you get the hang of it.

 

Well, as you stated above, yours definately has something wrong with it or maybe you have just adjusted the minimum air setting out so far the IAC cannot react to the needs of the engine. Remember, it will park open when you shut it down and adjust itself down after the engine restarts until it idles. Maybe you should try starting from scratch with the TB blades all the way backed down and go from there.

What is the idle set at in the PROM on yours though?

Like you are saying, everyone else should not follow what you are doing because you are basing your actions off of not having a functioning IAC system. Everyone else should get a scantool on their car and adjust the minimum air until the IAC counts are down in the 10-20 range (lower the better IMO) and then set the TPS - assuming they have an appropriate idle setting programmed in the PROM. Like if it is stock the stock setting and if it is like mine it would be 850-ish.....

 

I've done the minimum-air procedure a million times. I've changed the IAC (twice). I've changed the ECM. I've tested the wiring (3 or 4 times) and I even installed new pins and a new connector on the ends of the wires. I've taken the throttle body apart to ensure there isn't blockage. I've done everything I can think of, and no matter what, nothing makes it work right.

I think I have my warm idle set around 750 in the chip, but I've attempted to set the IAC with a stock chip with the same results.

I think my IAC problems are somehow tied to the throttle body, which would explain why these guys are going through the same things I did. I finally gave up and turned the idle screw to get my idle rpm, and I nurse the throttle until the car warms up.

Hopefully this winter I'll have time to toss the stock throttle body back on to see if that changes my IAC problems.

 

FWIW: When I set minimum air with the IAC disconnected, I set the idle RPM at 650RPM. Then, with the IAC connected it only has to be opened enough to make up enough air for another 100 RPM. The IAC counts would be around 10 to 15 when fully warmed up. On a cold start, the IAC counts might be around 80 for the cold ECM directed idle RPM of maybe 900 or so.

Could there be a problem with the Holley TB and how the IAC mounts?????

 

visually the IAC mount seems fine, but I don't know how well (if at all) it seats inside the hole.

I set my minimum idle at 550 rpm with the IAC disconnected. I hook up the iac, and the car idles at 550. At any time I can unplug the IAC and absolutely nothing changes. It is 100% ineffective.

 

Jim, I wish that I could help you with your IAC problem, In part payment for all of the good advice that you have given to me and others here on thirdgen. Anyway, it happens that you have done everything that can be thought of (and more).

 

Could this be a mix of the wrong year plenum and throttle body combo? I know the idle passages are different from the 85-88 ones and the 89-92 ones.... Putting one year TB on the other version of plenum will eliminate the IAC functionality.... I went through this a while back when I put an 89-92 TB on my 87 plenum and a buddy of mine had it happen with his TPI Suburban too but I don't know which one he had....

I mean if there are no codes for the IAC not operating properly but unplugging it or disabling it somehow has no affect on the idle speed I would have to wonder if it is allowing air through to the engine.....

It isn't that complicated of a system.... It's just a controlled vacuum leak really....

doc's method works exactly the same as mine - I just adjust and watch the IAC counts and don't bother with "homing" the IAC and setting the idle to a certain RPM. With my method you have to kind of play with it and watch all of the parameters like MAP signal and IAC counts and make sure there are no vacuum leaks or anything. Then when everything is all done just set the TPS and you are good to go. Either way you want to end up with as low of IAC counts as possible to keep the engine idling. This will result in crisp throttle action coming down to idle and lowers the chances of idle surging and the like. The IAC system is not all that quick to react and can have a tough time holding an idle at times depending on the conditions and engine combo so making it have as little affect on the idle air coming into the engine - the better.... At least IMO anyways....