Wild Idle After Accufab 75TB/Plenum and JLT CAI

[bgbg22]

Ok so i just finished installing my JLT Cold air induction kit, and the Accufab 75mm TB/ Plenum Combo. I had to go to the mechanic cause i snapped a bolt in half, but they took it out and they replaced the bolt. It was on the front/right part of the plenum, if u face it from front(hood).

Well anyway. I start the car and idle goes wild(its an automatic 00 gt), it just cant seem to stay in place it goes anywhere from 700-1200rpm while in park. Thought maybe the car just has to get used to the bigger CAI, cause the JLT piping is a massive 4 inches in diamter and a bigger TB/Plenum combo.

But then, i driven regularly, and i come to a stop at a traffic ligth n the rpms drop to practically 100-200, causing the car to jerk forward, it was like the car was pressing the gas for me to compensate, i almost nail the guy infront of me. i had to slam on the break, and the car just dies. I start it up again, come to the next light and it does it again. Now this is maybe two/three days after install. I have no idea what the **** is going on. When it was working, i noticed def an increase in power, and was pretty happy with the setup.

Its sunday night, and i let the car sit for a day since saturday, the mustang shops i know are open on tuesday, so hopefully it wont give me problems. But im gonna call Accufab to see if they can help.

Is it the JLT cai, the bigger 75mm tb, or the plenum. I dont know wtf to do. No lights come on in the car (check engines) so i figured everything was fine. But you can definetly tell something is not right, im figuring the air/fuel ratio has to be out of whack. I have no idea what to do, any suggestions?

 

[BurningRubber]

Is you IAC hooked up properly? Is the throttle screw adjusted improperly, throttle cable, kickdown cable, or cruise cable hooked up to the throttle body wrong?

 

[blkhorse]

you might want to unhook your battery and let the car relearn the idle.worth a try anyway

 

[bgbg22]

yes everything is hooked up properly, i just think there is soo much of a difference from the amount of air coming into the system. I checked everything, all the connections are fine, no leaks, nothing.

Any other suggestions?

 

[scupking]

I would suggest letting your car idle and play around with the throttle set screw. I didn't have the idle problem you have but my screw was set to tight and you needed extra pressure to press down the accelerator.

 

[the98stang]

The high idle makes me think you have a vacuum leak. Take a butane/propane torch and wave it around the plenum/TB area. The car idle will surge/change if you find the leak.

Also, reset the battery. The PCM might need to relearn because now you've introduced more air into the engine.

 

[2002tbstang]

adjusting the throttle set screw will most likely fix the problem. I had the same problem after I did all my intake stuff and it solved it because the throttle body blade was letting in too much air at idle

 

[bgbg22]

im going to try n set the voltage, but does anyone have any pics on doing this, or where the screw is located??

 

[nyuk98gt]

bgbg22:

If you bought a new TB, don't touch the screw yet. Check for leaks first and reset your battery, as the other posters recommended.

There is no point in adjusting your TPS, imo. The computer learns the closed throttle position at start-up. The computer doesn't care whether it changes every start-up. If you must adjust the stop screw, loosen it so there is a gap between it and the stop. Then, tighten the screw until there is exactly 0.010" gap. Then tighten it 1.000 (exactly one) turn and tighten the lock nut while holding the bolt so it does not move. This is the correct throttle stop position. You may have to increase the isc_air in the tune to perfect the idle.

HTH,

Chris

 

[2002BLGT]

bgbg22:

If you bought a new TB, don't touch the screw yet. Check for leaks first and reset your battery, as the other posters recommended.

There is no point in adjusting your TPS, imo. The computer learns the closed throttle position at start-up. The computer doesn't care whether it changes every start-up. If you must adjust the stop screw, loosen it so there is a gap between it and the stop. Then, tighten the screw until there is exactly 0.010" gap. Then tighten it 1.000 (exactly one) turn and tighten the lock nut while holding the bolt so it does not move. This is the correct throttle stop position. You may have to increase the isc_air in the tune to perfect the idle.

HTH,

Chris

the computer does not learn TPS at start up , you need to check voltage and make sure its under 1.0 volts on the signal wire with a volt meter , make sure you ground with the wires leading to the TPS , make sure you double check it once the engine is started to make sure the voltage does not climb over .99 after its running due to the extra voltage from the alternator output ...

 

[BLKsteeda]

you might find some info here on accufab's site

http://www.accufabracing.com/article_1.htm

 

[steve_stang2003]

the computer does not learn TPS at start up , you need to check voltage and make sure its under 1.0 volts on the signal wire with a volt meter , make sure you ground with the wires leading to the TPS , make sure you double check it once the engine is started to make sure the voltage does not climb over .99 after its running due to the extra voltage from the alternator output ...

Actually it does learn the TPS at startup, sort of....
The computer has a table built into it that equates throttle plate angle with TPS voltage.
The reason you want the TPS to be under 1.0 is because if it is too high a voltage at idle, you will not have enough room in the table to get to WOT.
This is highly over simplified and there is tons of wiggle room in this.
IOW, you have to have a really way off TPS to cause problems because the computer will compensate, to a point.
All it is doing is moving the baseline, which it assumes to be idle, up or down a little in the table.

That being said, I had horrid problems with my Accufab combo on my 2003 auto.
I had idle hang problems, loss of low end power etc.
I ended up returning the unit.
Everything was set up fine, no leaks etc.
It just sucked.

 

[2002BLGT]

Actually it does learn the TPS at startup, sort of....
The computer has a table built into it that equates throttle plate angle with TPS voltage.
The reason you want the TPS to be under 1.0 is because if it is too high a voltage at idle, you will not have enough room in the table to get to WOT.
This is highly over simplified and there is tons of wiggle room in this.
IOW, you have to have a really way off TPS to cause problems because the computer will compensate, to a point.
All it is doing is moving the baseline, which it assumes to be idle, up or down a little in the table.

That being said, I had horrid problems with my Accufab combo on my 2003 auto.
I had idle hang problems, loss of low end power etc.
I ended up returning the unit.
Everything was set up fine, no leaks etc.
It just sucked.

not going to make a big deal out of it , but the voltage is what it is , if its 1.0 or over its going to surge , the computer does not change voltage to the TPS after you crank the engine , it supplies 5 volts , and the tps gives back between .9-4.8 volts at whatever angle its set to ......if you dont believe me go put a volt meter on yours and get someone to crank the motor and shut it off 100 times and see if it changes , ill put any amount of money you want on it that it ( the voltage measurement) doesnt change ......I have gotten into arguements about this subject before with people who say the voltage wont change because of the alternator output , but I have seen it on several cars with my own eyes ........here is another forum , same topic , 2 guys in there have verified voltage going up after the engine running

http://mach1registry.org/forums/showthread.php?p=886482

 

[fudleyd]

The high idle makes me think you have a vacuum leak. Take a butane/propane torch and wave it around the plenum/TB area. The car idle will surge/change if you find the leak.

Also, reset the battery. The PCM might need to relearn because now you've introduced more air into the engine.

+1 Vacuum leaks are sometimes tricky to find...might wanna double check the o-ring on the plenum as well to make sure it isn't folded or pinched...good luck man.

 

[blkhorse]

put your old parts back on one at a time (starting with the jlt) and see where the problem lies.those parts are easy to change.

 

[bgbg22]

Yea well im getting 4.10's put in in about 2 weeks, the idle isnt as bad as it first was, im getting dyno tuned that day, so im gonna have the guys take a look at it.

 

[R.J.]

Here is a detailed write up that I found and should help you eliminate the idle setting as your problem.

DO NOT TOUCH THE GAS PEDAL!!

What you will need: a mutlimeter, a big screw phillips screwdriver and some sort of small metal piercing tool
What will be handy but not necessary: an extra set of hands, a scan tool that will give you live data readings. you can rent one from O'Reillys or Autzone.

You will probably get a million different responses on how to do this. This is how I have done it and it works for me. And I've done it a lot. Refer to short in PCM wiring
1. Disconnect the negative terminal to your battery and turn on your headlights for about 10 minutes(there's a lot of speculation as to how long. some people will even say to disconnect the positive terminal and some people will say to leave it disconnected over night.)
2. Disconnect the wiring harness connector to the IAC
3. Turn off headlights and reconnect battery. DO NOT TOUCH THE GAS PEDAL!!
4. (People will probably argue over this step) DO NOT TOUCH THE GAS PEDAL!! Try to start the car. If the car won't start adjust the set screw on the throttle body a 1/4 - 1/2 turn and try again. Repeat until the car will stay running. It will run rough but that is what you want. (some people will say to turn the set screw a few turns before starting your car then turn it down until the car idles at 700rpm or so then)
5. Either way you go let the car sit and idle (DO NOT TOUCH THE GAS PEDAL!!!) until the car reaches operating temperature which to me is when the needle moves to the right leg of the letter 'N'
6. DO NOT TOUCH THE GAS PEDAL!!! Step 5 allows the computer to relearn idle settings. It's pretty cool when you follow my procedure because you can actually hear and feel the car figuring out the proper idle settings. It will go from idling rough to idling smooth as it warms up. Once the car is warmed up verify that the car is idling at around 700rpm. (this is where the scan tool comes in handy cause you can be more accurat but eye-balling it works too) If the car is not adjust the screw until it hits ~700rpm and then let is sit maybe another 10 minutes DO NOT TOUCH THE GAS PEDAL!!!

DO NOT TOUCH THE GAS PEDAL!!!

Turn the car off. Reattach IAC wiring harness. Now some people out there will tell you that this step is not necessary but I totally disagree. Remember we adjusted the set screw on the throttle body. That means that the voltage reading from the TPS sensor has changed. It should read between .96 and .99 volts. (someone correct me if I am wrong) Anything outside of that range will cause all sorts of issues including misfires and rough idle.

7. Now this part you may want to look up and verify before you go piercing wires. What I do is I stick the middle wire with a metal pin, a heavy sewing needle works pretty good (I think, it may be the top wire if you are viewing the connector while still connected) some people just peel off a piece of plastic wire cover because they have to do this so often.

8. Set your multimeter to volts. Turn your car to key, on engine off. then place your positive lead of your mutlimeter on the metal pin and your negative to some ground point. If it comes up as a negative that is okay as long as you are -.96 to -.99. If you get this reading then great you are done and hopefully your issues are gone. If not procede to step 9

9. This is where and extra pair of hands come in handy. Using a large screw driver you will need to loosen the bolts that hold the TPS. DO NOT USE A SCREWDRIVER THAT IS TOO SMALL BECAUSE YOU WILL STRIP THE BOLTS. They probably will be really tight so you have to really lean on the screwdriver and use some finesse. They will come off. Just don't try to turn the bolt all at once or you will strip it. A lot people have broken their TPS from being too rough with these bolts. Again, I'm not a mechanic by any means but just use some common sense.

10. Once the bolts are loose you will need to move the TPS up or down and continue to read the voltage. Once you get it to the desired setting you can retighten the bolts. What I do is I find .97 and then as carefully as possible I tighten the TPS down. what will happen is the voltage will change usually to
.96 or .98 but that it okay. Once you are done with this manually open the throttle body a few times and close it then reread the voltage and make sure it is still withing our desired range.

11. You should be good. I would put a little putty on the whole you made with the pin. Drink a dozen beers or so and crank you car. DO NOT TOUCH THE GAS PEDAL!! I would give the car a once over, make sure nothing came loose while you were messing around under the hood. Let the car idle for a few minutes then take her for a spin. You may want to wait on the dozen beers.

I hope this helps and fixes your problem. Like I said I had a similar issue and it turned out to be a cobination of a bad set of MSD wires only a few months old and a bad TPS. Shortly after that my EGR valve S%^T the bed and then my car developed a short in the lead wire for the PCM effectively resetting the computer every time it blew a fuse. But, I hopefully have it all fixed now. My car has been running smooth with the exception of a slight misfire due to some corrosion on one of the spark plug wires. I cleaned the connectors and have been golden since.