Stock MAF, ported TB, LS6 intake, ported heads, TR220/.553/114 cam, FLPs ... '98 Trans AM

Had it tuned and the results are in another thread.

When coming to a stop, the car would hunt for idle and finally find it.

Was told to drill out the TB plate.

I have a set of drill bits graduated in thousandths.

I found the drill bit that just fit into the feeder hole @ .165 ....
I inserted the next size up @ .169 and drilled it straight in. Took the slightest amount of metal. I had a rag behind it and cleaned the TB bore before removal.

Now the car stumbles when the throttle is opened. It's worse when cold and but almost non-existant when warmed up, at least I think I still feel it.

Any insight?

Does the PCM need more time to learn?

 

Mitch- where is your idle speed set? With idle set at 900 RPM (Ed Wright programming), I didn't have to drill the TB at all with that cam. No hunting or surging- perfect idle and drivability. Either your idle speed is too low, or your tuning is a little off, IMO.

 

Just <img border="0" alt="[driving]" title="" src="graemlins/gr_driving3.gif" /> it! <img border="0" title="" alt="[Razz]" src="gr_images/icons/tongue.gif" />

 

Is your ported TB epoxy-filled? If so, the air holes may be too small.

Do you know what your IAC counts are?

 

Just a few things off the top of my head:

I'd check your idle speed. With that cam you can get away with 800rpm idle. Use autotap and get a good IAC reading. At warm idle with no accessories on it should be ~30. With the A/C on ~45.

Another thing you can look at (if you have LS1edit) is the IAC park position and in gear settings. This setting tells the IAC motor what step count to go to when you're in park, and when you're in gear when you let off the gas.

I'd also pull your IAC motor and see if it's just dirty. Take the time to clean out all the air passages in your TB. If these are blocked, even partially, you'll have issues with idle.

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by mitchntx:
<strong>Just stumbles when opening throttle from closed or partially closed. And only real apperant when cold.

Also, it is idling at 1100+ via the stock tach</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Do you two-foot your start? IOW, do you push in the throttle to give the car gas when you start the car? If so, you may be making it harder for the car to learn how to start.

Check the throttle body blade at idle. With the car off, try opening the throttle body blade with your fingers. Is there a "sticking" near the closed position? If so, your closed position might be too far closed. You can adjust with the screw at the base of the TB. Again, using Autotap, check the voltage when your TB is at idle. I believe the spec is ~0.6V. If I'm wrong, someone please correct me. And again, keep the IAC counts ~30.

Stock tach LOL...my tach was off anywhere from 300-400rpm. Use AutoTap to find the real idle. Take off your console and adjust accordingly.

 

I set mine to 900 and runs like stock <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

At cold start, it hunts for idle for about 4 seconds and then runs stock smooth.

Someone please define the acronym IAC for me <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by mitchntx:
<strong>
Now the car stumbles when the throttle is opened. It's worse when cold and but almost non-existant when warmed up, at least I think I still feel it.
</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Clarify ... it no longer hunts.

Just stumbles when opening throttle from closed or partially closed. And only real apperant when cold.

Also, it is idling at 1100+ via the stock tach

It's been really nasty here the last couple of days.

I will get IAC counts ASAP

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by The Dragon:
<strong>Someone please define the acronym IAC for me <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">IAC = Idle Air Controller