Solving Idle/surging Issues With Iac Mod

varunner

New Member
Jun 16, 2014
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Hi All,

I'm a new member here. I have a 95 mustang GT auto trans. Engine is stock except for headers, CAI. I recently added a different cam, very mild specs. So as others have experienced, the idle is rough, somewhat expected, but the problems is that it dies when put into gear, and also pretty bad surging in idle and in gear. I checked thoroughly for vacuum leaks. So after searching for help by moding the IAC, I put an extra gasket in place and cut through both of them creating an open space between the 2 air holes giving it a constant by-pass. At the same time I re-set the idle using the procedure found on this site. This greatly improved the idle, and eliminated the surging, and so far it doesn't die when put into gear. So my question is how do I fine tune this modification ? Just by ear ? O2 sensor reading ? I don't have a WB O2 now, but plan to. Thanks in advance. Great site btw.

Brian
 
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They actually make a little plate that goes under the IAC that you can adjust the bypass with two little allen screws. It's not very expensive. It's something that we used to use in the long long ago. Now everyone runs a tune anyway, and you can adjust it through the tune, so there really isn't a need. Do you happen to know what your vacuum is at idle?

Kurt
 
Vacuum at idle is around 15" I have a tweecer. Do you know if the bypass can be regulated with a tweecer ?


They actually make a little plate that goes under the IAC that you can adjust the bypass with two little allen screws. It's not very expensive. It's something that we used to use in the long long ago. Now everyone runs a tune anyway, and you can adjust it through the tune, so there really isn't a need. Do you happen to know what your vacuum is at idle?

Kurt
 
15" of vacuum is plenty. You should be able to adjust the IAC to hold a good idle with a tweecer without any bypass modification. Keep in mind that the IAC is a common failure item. An old IAC can cause problems controlling idle.

Kurt
 
Unfortunately I have no experience with the tweecer. We used to have quite a few people on here that messed with the tweecer setup, but most people have swapped to the Moates Quarterhorse now. I've never messed with either.

Kurt
 
I found about 6 different settings for ISC in the tweecer. A couple of them deal with idle speeds, so I'll have to try a couple of things. Not sure if I'll undo what I did to the gasket or not. Sure would be nice if I could find some good tuning info. Just a little info here and there. thanks

Brian
 
Seems all is good now. In addition to the gasket mod I did, I found a conflict within tweecer. There was an idle setting associated with the ISC that had to be within 100 rpm with the Idle in neutral and Idle in gear setting. Thanks for the help.

Brian