Back with another problem

No.Morning.Sun · Oct 3, 2011

I just put in a new upper intake plenum and 75mm throttle body. the car runs like a champ, and feels a lot more powerful. the only issue is the idle is all funky now. when I start it and when I push in the clutch to roll up to a stop it revs to 2000 and stays there for a while before dropping to 1000. it threw a code this morning so I went and had it read. it was the IAC. is it just confused? should I disconnect the battery or do I need to use a tuner? or am I gonna need an after market IAC to accommodate the added airflow?

on a side note, i think my next mod will be a CAI. recommendations? offers?

Musturd · Oct 3, 2011

Try resetting the battery.

No.Morning.Sun · Oct 3, 2011

will do, get back to you in 30 minutes

Musturd · Oct 3, 2011

Otherwise ur iac is prolly messed up you could try cleaning it unplugging and plugging back in.

No.Morning.Sun · Oct 3, 2011

resetting the battery didnt work, so im gonna unplug it and plug it back in see if that helps. otherwise im just gonna run it like this for a while, im not trying to spend 200 bucks on a IAC for a throttle body I get for free haha

mygreengt · Oct 3, 2011

how long did you leave the battery unhooked for? when i did mine, i waited 20-30 mins, then let it idle for a while

No.Morning.Sun · Oct 3, 2011

I left it off for a little over 30 minutes. I let it idle for maybe 3 minutes listening to it. the light isnt on but it still revs to 2000 before leveling out at 1000 so the light will prolly come back on.

mygreengt · Oct 3, 2011

all vacuum lines connected and in good shape? you could have put a hole in one or something.

No.Morning.Sun · Oct 3, 2011

not sure. are you talkin about all the hoses running from the air intake hose? they are all good. it does make a strange noise when I have the heat on though. every once in a while something makes a purging sound, only happens when the heats on though pretty wierd.

Im so new at this haha, still workin on the basics.

Willis_98GT · Oct 3, 2011

Sounds like the iac isnt reacting like it should, look into the iac mod

basically you need to space the iac from the plenum, by making a thick gasket so that your rpms will drop faster, very popular mod

joekd · Oct 3, 2011

Disconnect the wire on your IAC and see what happens

No reason at all for an aftermarket IAC (if anyone even makes one) I have a 75MM TB and plenum on my car and my idle is perfect

MustangChris · Oct 3, 2011

just get a new IAC. any "aftermarket" one is going to be an OEM manufacturer (such as ACDelco) anyways, theres no such thing as a "performance" one.

id find a friend with a properly running mustang and borrow his IAC for a few minutes. see if that fixes the problem....

also, you can not "clean" or "service" IACs. they must be replaced.

Kidd · Oct 3, 2011

you need to do an idle reset.

No.Morning.Sun · Oct 4, 2011

MustangChris said:
just get a new IAC. any "aftermarket" one is going to be an OEM manufacturer (such as ACDelco) anyways, theres no such thing as a "performance" one.

id find a friend with a properly running mustang and borrow his IAC for a few minutes. see if that fixes the problem....

also, you can not "clean" or "service" IACs. they must be replaced.

Ill give that a shot. I kinda doubt that my IAC is messed up it worked fine on my stock plenum and throttle body. all i did was switch them out

reivaxtorres · Oct 4, 2011

do you have a code scanner or tuner that will give you the live data off the computer? ill bet that your TPS is off. either get a scanner/tuner to see what the voltage is on the TPS, or get a voltmeter and measure it. key on, engine off, and it should read .98V -- any thing more or less, and you need to adjust the set/stop screw to get the voltage where it needs to be.

just one of a few possible causes.

Willis_98GT · Oct 5, 2011

reivaxtorres said:
do you have a code scanner or tuner that will give you the live data off the computer? ill bet that your TPS is off. either get a scanner/tuner to see what the voltage is on the TPS, or get a voltmeter and measure it. key on, engine off, and it should read .98V -- any thing more or less, and you need to adjust the set/stop screw to get the voltage where it needs to be.

just one of a few possible causes.

so by just adjusting the set stop screw you can cause problems?

reivaxtorres · Oct 6, 2011

Willis_98GT said:
so by just adjusting the set stop screw you can cause problems?

Cause or solve problems. If it's stock and never been adjusted before, you will cause problems. If it's aftermarket and it's mis calibrated, messing with it will correct the mis calibration.

No.Morning.Sun · Oct 9, 2011

im going to try adjusting the screws today, I will post back afterwards

Bullitt5339 · Oct 9, 2011

You guys are all over the place on this one........lol

Verify it's not the IAC before moving to the TPS or adjusting the set screw. Mine was doing the same thing, and it was sticking. A quick test to see if it's sticking is to rev it up and while it's stuck on high idle, tap the IAC with the plastic end of a screwdriver. If it immediately drops back down, the IAC is sticking. You can try to clean it, but that's never a definite fix. As someone mentioned before, the correct way is to replace it.

Then move on to checking the TPS sensor.........
Then move on to making sure the set screw is correct.......

There's no reason to try 4 things at once. Check one out at a time, from the most likely to the most unlikely. Eliminate them one at a time as a possible cause and move on or else you could make things even worse.