Idle Adjustment Screw

I have a 97Z and I just put a BBK 52mm TB on it. If the idle is adjusted by the computer and various sensors, why is there a idle adjustment screw on the TB? I need to adjust it because my idle is too high because of it, but didn't want to just bottom it out if it actually had some purpose.

Thanks,
Anthony

Adjusting it will. If the blades are open too much the PCM can close the IAC and then after that there is nothing else it can do to reduce air flow. If the blades are too far closed the car can open the IAC as far as it can go. Then after that it can't do anything else to increase air flow.

Back it off SLOWLY until you get the specified idle speed, which is 800rpm for your M6. Remember the stock tach typically reads 100-200rpm higher than actual. If you put a scanner on it, you can read actual RPM from the PCM, then check the IAC counts to make sure they are in the range of 20-40, and finally check the TPS closed voltage to insure it is between 0.20-0.90V, preferably 0.50-0.70V.

Ok, sounds good. I put AutoTap on my car this afternoon and also found out that my TPS is reading open 15% at idle. Is this normal? I figured that it should read 0% or close to it at idle, right? I got a DTC for the TPS Low and Intermitent voltage. I'm going to the store to get a new one and replace it anyway, but was wondering if that could be the reason for my idle to be around 1200 or so in conjunction with the idle screw.

No, 15% TPS at idle is wrong. The screw is out too far. The PCM looks for a TPS voltage between the 0.20 and 0.90V that I mentioned above. Whatever value it sees at startup, as long as it is between those values, will be set as 0% throttle position. Look at the TPS voltage with AutoTap and you can see that yours is well above 1.00V, which sets the code.

Your idle is not high because you have a bad TPS sensor. Your idle is too high because the throttle stop screw it sticking out too far and the blades don't close correctly, keeping the TPS voltage too high.

If you back off the screw and the TPS voltage does not come back down to an acceptable value, you need to verify that you have correctly indexed the flats on the blade shaft to the sensor.

I backed down the screw and everything seemed fine while just sitting there idleing. Once I drove it around it bounced back up to about 1200rpm's again. I pulled out the AutoTap and it said the TP angle was at 21.2% and the TPS was at 0.8 volts. From what I'm getting from your reply is that I need to pull the TPS and index it correctly with the blades closed, right? I'm at work so I can't try it right now, so I want to make sure that way when I get a chance I can do it correctly. FYI, my IAC counts are at 97. Is that acceptable?

Thanks,
Anthony

Is this a new or used TB? If used, did you clean it before installing? I found when I cleaned mine that the RPMs would "hang". Dab some oil on a Qtip and lube the butterfly rod where it enters the TB housing to eliminate the hang.

It's a used TB. I'm not sure if my brother cleaned it before he installed it. I talked to him and he said that he might not have installed it correctly. I'm gonna go back and double check it just to be sure. I'll also check out the butterflys and see if anything seems amiss.

Anthony

BBK's are prone to sticking blades. Try cleaning it with some carb cleaner, the spraying it with a healthy does of penetrating lube. If it goes away for a while and comes back, your just going to have to keep lubing it up until you get tired of it and sell it like i did mine...lol

-Shannon

BBK's are prone to sticking blades. Try cleaning it with some carb cleaner, the spraying it with a healthy does of penetrating lube. If it goes away for a while and comes back, your just going to have to keep lubing it up until you get tired of it and sell it like i did mine...lol

-Shannon


Mine stuck sometimes. I just cleaned it then installed an extra throttle return spring on the spare hook on the TB. It works flawlessly now.