surging idle.... won't idle on its own after heads and TB install

[95CobraMike]

Well i just got done with my engine rebuild....
while rebuilding i put on some ported TW heads and a BBK 75 mm throttle body

put everything back together and it will not run on its own.... it keeps dying
but i can keep it going if i put my foot on the gas a little and hold it to about 1700 rpms, at that point, it runs good....if i let it fall any like to 1200 rpms it goes nuts....down to 1000, up to 2000, down to 1000 and back up....

the bbk throttle body says it comes preset for our cars as far as the idle screw goes. i also checked and set the TPS voltage to .985, and cleaned the IAC i have read and searched quite a bit on the topic, but i cant seem to get this thing to run on its own.....

BTW i am not sure of the timing becuase i cant get it to idle to set it....

 

[bimmertech]

vacuum leak is my guess

 

[95CobraMike]

i will check them, but i am pretty sure i dont have one.........

as far as vac is concerned, you have vac connections
-3 by the throttle body
-2 under your upper intake
-1 in the brake booster
-a few under the supercharger
am i missing any?

 

[Pokageek]

Let me save you $1200 that I paid. You can't just slap an aftermarket MAF on your car and call it a day. Mine had to be programmed BIG time...Car wouldn't run right until I did that. Good luck.

 

[95CobraMike]

The MAF on the car has been on the car for over a year and it has been dyno tuned into the mix
i dont think thats the problem

 

[Pokageek]

Vacuum leak. My bet.

 

[94opalgt]

i dont see anything in your sig about a self tuner or a chip burnt for the car.if you have no vacuum leak then your car needs tuned,either a self tuner or have a chip burnt for it. the only way i got my car to idle and run correctly is to have a chip burnt for it,its a sct chip.i didnt even change my cam and i had to do this.

 

[ES Stangin]

it has been dyno tuned into the mix

His car has been tuned..

 

[94opalgt]

well how did he get it tuned if it wont idle correctly?has it been tuned since the swap?he didnt say it was tuned with the new heads and tb on it.from what he said the car was tuned before the swap right?well if if it wont run after the swap and there is no vac leak guess what?it needs tuned again.

 

[R.J.]

My buddies 94 GT did the same thing after the same exact mods and this was the only thing that fixed it:

Begin with a cold vehicle. The idea here is to get the car to a firm cold idle with enough air bleed capacity left in the idle circuit for IAC adjustment.

The idle stop should be set first. Back out the idle stop screw, away from the bell crank arm, until about 1/2 turn past the point where it no longer makes contact (blade fully closed). Using a 0.010" feeler gauge, tighten until gauge just drags between screw and bell crank arm. Remove feeler gauge. Tighten screw exactly 1 1/2 turns. If the screw is very loose, put a drop of loc-tite or silicone on it, so it doesn't work out of adjustment.

Now remove the connector to the Idle Air Controller (IAC) just on the other side of the throttle body. Start the car and allow vehicle to warm for 2 minutes. Give a small "blip" to let it settle. If it is having a hard time staying running you may have to get an assistant until you can get to the front of the car. Now open or close the air bleed screw (CCW opens) next to the IAC until the car idles at 575 to 600 rpm. For guys with aftermarket cams and an EEC tuner, you might want to idle a bit more briskly, say 650 to 675.

Obviously, this rpm range is by what the car and driver wants...IE, no set idle speed, whatever works for YOU.

Turn off the car. Now count the number of turns clockwise to close on the idle air bleed screw. If it falls between 1/2 and 2, it's okay, now reverse it out the same number of turns. Log the number somewhere in case you need it for the future. Reconnect the IAC. You are done.

If the air bleed screw is above 2 turns, it's a good idea to tighten the idle stop screw another 1/2 turn, and then repeat the idle setting. If it is below 1/2 turn, then loosen the idle stop screw by 1/4 to 1/2 a turn, and repeat the idle setting. Be sure to put another drop of silicone RTV on the stop screw if it was disturbed. Reconnect the IAC. You are done.

 

[95CobraMike]

it was a vac leak!!! one of my couplers on the S/c wasnt tightened all the way...... i feel like an idiot... but it runs now and it sounds niiiiiiiicce

to clarify the car was tuned yes....but no not since the heads and TB

i might have to adjust the base idle though, its around 850 right now and some of the times it stalls out when i let off the gas or right when it starts, after the initial rpm jump from the starter...
so once i do that, things should be working well....thanks for the help!!

 

[Pokageek]

it was a vac leak!!! one of my couplers on the S/c wasnt tightened all the way...... i feel like an idiot... but it runs now and it sounds niiiiiiiicce

to clarify the car was tuned yes....but no not since the heads and TB

i might have to adjust the base idle though, its around 850 right now and some of the times it stalls out when i let off the gas or right when it starts, after the initial rpm jump from the starter...
so once i do that, things should be working well....thanks for the help!!

Glad you found it man. I know that can be frustrating.

 

[ES Stangin]

Its always a nice feeling to have found the problem..

 

[94opalgt]

great to hear you figured it out.