Thread: I have an issue I cannot seem to figure out...

Ok guys,

I have a slight issue I cannot seem to figure it out. I'm really in need of some help.

Recently I just got done ridding my car of Garlock gaskets, so pretty much removed everything above the LIM. The IC, S/C etc. I RTV Both sides of both S/C gaskets and reinstalled everything. I had my TB redone by Brain (did a fantastic job BTW, I definatly recommend his work). When I got the TB back I cleaned it out with carb cleaner and what not. I noticed the TB blade didn't look adjusted right and I could see a good amount of light around it. So I adjusted the set screw so it could close better. I turned it until it barely cought and backed if off a 1/4 turn so there would be no interferance.

Why did I mess with this? Well about 4 years ago somebody had a free mod where you would take your TPS sensor, drill out the holes so it could be adjusted. After adjusting it to a certain value you'd adjust your TB blade. Well I tried it and it didn't work good for me, infact it made my tranny slip! So i reversed it, or so I think anyway, its been so long. Anyway, i never had a problem again.

Today I was driving my car, and it was running fine! Ran smooth, oil pressure good, vac at 19-20 in vac, everything looked, ran, and sounded good! With that said, I was flipping though my Scanmaster checking various values and I found one odd problem. My IAC were going anywhere from 15 to 0. ?

I went home, all evening i've been messing with adjusting the TB plate etc. A couple of times I got the IAC at 130 at idle and off at 255, then adjusting more it would go back to 0 and 120 off. Basically what it does, I start the car, it starts at 57 and rapidly drops to 0. Car runs good, sounds good. Once it threw a code, which was PO1404. Which is an EGR code, Makes no sense to me, I don't even have an EGR! Haven't had one in years. I checked all the vacuum connections. I used a can of carb cleaner on the whole engine bay and no funny idling at all. Other than the scanner saying the IAC at 0, the car runs and drives fine! The vac at idle is at 19-20 in vac, so thats good. I don't think the IAC is bad either, I took the one off her car and tried it in mine, same issue. Put it back in her car, and her car runs fine and the IAC are where they always were.

I'm baffled, help?

WOW, looks like i'm all alone in this situation.

do you have any previous scans?

Overkill did that write-up you were talking about and it worked fine for me. Since you adjusted the the screw did you go back and look at the TPS voltages to see if they are within the range they are supposed to be?

here is the write-up in case you want to verify your settings.
Ontario Quebec Club Grand Prix :: Throttle Position Sensor Optimization

Does sound like you are getting unmetered air from somewhere. If you weren't, and the IAC were 0, I would think the car would run badly.

I just look at one of my last scans and my IAC is between 17 and 20 in gear at idle, but I also have a hole drilled in my TB blade.

No previous scans at all.

As for a vac leak, i'm about 100% sure thats not this issue, seeing how i'm idling at 19-20 in vac and I used a can of carb cleaner to find a leak (change in idle) and that did nothing. I'm pretty sure its something to do with the plate, its gotta be. I bet if I would of reinstalled it and left it alone i'd never have a problem. Sometimes a guy should screw with **** like I did, thats the moral of this story. As for the HVTB, yeah, it opened up throughout 72mm w/ a 72mm plate.

Thanks for finding that TPS mod! I've been looking for that. I know I tried it and it didn't work for me at all.

As for unmetered air, with how my vac is I don't see that being an issue. Car runs great and the vac is where it should be. Where could get unmetered air other than the S/C gaskets, vac lines, and TB gaskets? They seem to be sealed up good.

BTW, why do you have a hole drilled in the TB plate?

The hole in the TB, increases airfow. There are not enough Idle Air Flow tables to do adjustments like the V8 guys can, when adding an aftermarket cam. This helped with cold startups. Dave gets the credit for this. He said with the cam the PCM will think the car is running lean and add fuel, essentially now making it too rich. Drilling the hole helps lean it out some. I've seen where some of the LS1 guys with really big cams do this to suppliment the tables that they are able to tweak.

Overkill mentioned drilling a hole as well.iirc

Really? Wow, i've honestly never heard of that being done. Then again i'm more used to cammed carbned cars vs FI. Thats good info to know for the future if I ever cam my car or another FI car. Speaking of which, how big of a hole are we talking? Anywhere on the plate?

Well, still no luck. I confirmed again i don't have a vac leak......19-20 in vac at idle, LTFT at 0.... all that is where it should be

Originally Posted by Iron Indian

Really? Wow, i've honestly never heard of that being done. Then again i'm more used to cammed carbned cars vs FI. Thats good info to know for the future if I ever cam my car or another FI car. Speaking of which, how big of a hole are we talking? Anywhere on the plate?

Supposed to start with a 1/8" hole in the center of one half of the blade Like a dot in the middle of a D. Then step up from there as needed. I left mine at 1/8 which did help btw. Dave can give better details, if need be.

Ok, well. I messed around adjusting the plate again. I took a look at my stock TB and the plate is completely sealed around so I figured the aftermarket should be the same. So I backed the set screw all the way off until it wasn't touching and ran it in a 1/4 turn, much like I had it when I reinstalled it. I poped in my original IAC valve and reset the PCM a few times. At idle in park its reading 27 although it was at 40 for a time. How long does it take for the IAC to properly adjust?

27 should be fine. When it is sitting at 0 then the pcm has no control over idle rpm anymore and often throws a code. You want the throttle blade to have a good seal all the way around, NO light and it should touch the bore. If it is even the smallest amount open then you have a lot of air getting past it that shouldnt and is why the iac count goes down to zero.

Thanks!