General Z

Hey guys,

Sometimes I wish I had jsut left well enough alone on my car. LOL.

Anyway, I did the home port and polish on my throttle body. I was very conservative. Did not do anything around plate circumference. Ever since cam install, car has always idled really rough. I figured while I was in the throttle body, I might as well drill hole larger to fix idle.

Drillign hole worked. I figured, if a little is good, a lot must be better. I drilled hole larger. Well, hole was too large. IAC counts at 0 and fast idle. I read a post about flipping idle screw over and using that for adjustment. I did it. I also read about filling in throttle body plate hole with a rivet. I did this.

I tried using idle screw to get IAC counts between 30 and 50. At about 38, the car is idling way fast, like 1200 to 1500. So, I turn screw in just a hair. Idle goes down, but IAC is at 0. Repeated this several times, never got a good medium.

I have tried a trick I read about, unplugging and repluggin TPS sensor in. That did nothing and my Scanmaster showed TPP at 1 before and after, unless I turn screw. I also tried unplugging and plugging IAC as I have read this resets it. This did nothign either. I also pulled PCM bat and IGN fuses and restarted. This also did not help. I am beginning to think I need a hold in throttle plate and use screw to fine tune IAC, or just make a smaller hole than I had until IAC is between 20 and 50.

Please help. ideas?

Thanks, sorry for long post.

P Mack

iTrader: (6)

What fuel trim cell are you in? If you're not in an idle trim cell, the iac won't adjust to your idle speed.

General Z

I don't really understand fuel trim cells. I have a scanmaster, which shows the cell, but I don't know what number I should be in. Can you tell me what one I need to be in, or how to change what one I am in? Isn't it a reflection of several factors, including TPP and other stuff?

Thanks

wait4me

iTrader: (10)

you do have a small hole in the blade still right? or did you rivit the hole shot completely? cell 16, 17 18 or 19 is what you should see at idle, and sometimes at warmup , you will see cell 22..

General Z

I riveted the hole completley shut and figured I would use the idle screw to adjust it. That's where the problem is coming in. I think I can't do a small enough adjustment. Must need a small hole as a helper, then fine tune with screw?

What if idle is not in proper cell?

Thanks again.

wait4me

iTrader: (10)

that is your problem, you need that hole in there, i would just settle with when you had it at 38, that is fine, if you adjust too far with your throttle set screw the computer starts to not be able to learn the starting position of the tps sensor, so it will no longer read 0% thottle, so it thinks you are pressing down the petal..

General Z

With Iac at 38, my rpm's are 1200 to 1500. That's too high right? I guess I will have to drill another hole and keep the riveted one riveted.

wait4me

iTrader: (10)

? high idle? there are no vacuum leaks right? does the car run like crap if you just turn the set screw on the blade and shut it more? if it is high idle that means that the blade is open too much, and the iac motor cant take out anymore air..that is why you drill the bigger hole so the iac motor doesnt have to work so hard. making the car surge or stumble or die..

RPM WS6

iTrader: (3)

I have found the 30-50 IAC rule that many go by doesn't work for every car. Anything below about 45-50 and I start to get idle hang. I'm at the 58-62 range right now and have very few hanging issues. When I was in the 3X range it would hang often. I may try to get back to the 48-50 range though, seemed to be a slightly more stable idle at those values..... Still gotta try some more tuning tweaks first though.

Stock hole size is 5/32" BTW.

General Z

No vacuum leak that I can find. I already redid my PCV system to eliminate my one vacuum leak. Should be sealed up quite well, I think.

Car actually runs quite well if I close the blade more. But, IAC goes to 0 when I do this. Car idles just how I want it too. However, I know you don't want IAC at 0. So, I am thinking, I should adjust idle screw until TPP reads 0 instead of one, and start drilling progressively larger holes until I am idleing well, and have a good IAC count? Is this right, or with a hole drilled, can I still use the idle screw to fine tune?

Thanks again

P Mack

iTrader: (6)

Exactly. And you can tell if the computer thinks that by looking at what cell you're in. You're right about cells 16-19 being closed loop idle cells, but i'm pretty sure the cold idle cell is 20, not 22.

General Z, this picture has helped me a lot with understanding fuel trim cells.