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I have an idling issue with my 383 LT1. The camaro will fire right up and idle normally (1100rpms), but as soon as I apply throttle it wants to idle at 400rpms for a second and then kick back up to the 1100rpm. I have had my tuner look into the issue and they have adjusted many parameters in the tune several times. I replaced my IAC valve with a GM part (car starts better, but still a wobble in the idle). With the old IAC I had to give a little throttle to get it started sometimes. The car doesnt lean out under throttle either. Any help would be appreciated (I'm at the end of my rope hahaha)!!! See video here:
I have an idling issue with my 383 LT1. The camaro will fire right up and idle normally (1100rpms), but as soon as I apply throttle it wants to idle at 400rpms for a second and then kick back up to the 1100rpm.
-BBK 58mm throttle body
This may be your culprit. Mine used to do the very same thing and after several start cycles (maybe two tanks of gas?) it would level out. Reason being is my TB had no idle hole drilled into it so the IAC had issues with trying to find the right idle speed. Once the PCM learned then it was fine. I don't remember if those BBK's have an idle hole or not, but you can either search here or google "LT1 throttle body drill mod." So, you can either live with it and see if it clears out after a few weeks, or try the drill mod if your TB does not have an idle hole. Just know if this is the issue every time you remove power from your PCM you'll have to go through this all over again. Once I drilled the TB I never have an issue after resetting/removing power.
Interesting; I will see if my BBK throttle body has a IAC bypass hole. I was reading some people just adjust the throttle blades to be open a little rather than drilling.
I don't remember. Did it years ago. Try a search on this forum. Unless you have an adjustable throttle position sensor you don't want to adjust the blades.
I'm definitely going to check the BBK throttle body to see if that hole is there. I just checked the stock throttle body and it looks to be about an 1/8" hole in it.
That is a good thread! Thank you. I sure hope this is the solution.
Just checked. The BBK 58mm throttle body doesn't have a hole, but my stock throttle body does. Im gonna pull it and drill it 1/8" to start. I'll do a coolant bypass while im at it. I'll update the thread if this fixes it. Thank you for your help!!
First off, I performed a throttle body coolant bypass for all of $4. Super easy to do! 😃
Next, I removed the BBK 58mm throttle body and drilled a 1/8" hole with a drill press. I cleaned all the shavings out. Then, I put it back together and fired it up. It idled like garbage for 30 secs before slowly creeping up to the 1100rpms (im guessing the computer was relearning the IAC sensor again after unplugging it with the battery disconnected).
After that I gave some throttle input and it stumbled up the rpms, and then went back to a low idle again. This time it seemed to drop to about 700-800rpm and occasionally dip to the 400-500rpm range before creeping back to 1100rpm. I ran it for about 10 minutes total.
I turned it off checked for coolant leaks and then restarted. It fired up more naturally, and idled at 1100rpm and throttle input didnt cause it to drop to low rpms (it did this before the drill mod too).
I measued my stock throttle body IAC bypass hole and it appears to be between 5/32" and 11/64".
I took it out this afternoon. It idled at 1100rpm like it should and rpms returned to 1100rpms after throttle input. Usually when I let it cool down all the way it has the idle issue. Im gonna test it all week to see what it does.
I've read many forum posts saying the stock one is supposed to be 1/8"... but mine is definitely 5/32" (fAcToRy FrEaK lmao). See pictures below:
Im gonna take it to my tuner and log the IAC counts before I drill more.
I appreciate the help!! I'll make updates with progress or issues I encounter.
you really need to be monitoring your IAC counts before doing ANY drilling. Stock TB is 1/8" hole. Cam cars needing slightly higher idle than stock (850 rpm) often need the hole larger. drill in 1/64 increments until IAC counts at idle are 32 (30-35). On my 383 using a stock TB bored to 52mm my hole is 11/64"
1/64" larger makes a considerable change. You can't "undrill" so scan IAC at each step of drilling bigger
even with a hole on aftermarket TB's, some have different air passage machined in them than stock so compare aftermarket to stock. IMHO unless you are making over 500hp, a 52 is better and the 48 is certainly good to 450.
Definitely makes sense. My BBK 58mm appears to have the same passages as the stock one minus the IAC bypass hole.
My engine made 520hp/485tq (crank) and I think it dynoed like 440rwhp/415rwtq on a pretty hot day. The intake is ported to 58mm too.
My stock throttle body IAC bypass hole is definitely 5/32" (1/8" and 9/64" drill bits fall straight through the hole with ease, where as the 5/32" is a perfect fit and moves easily).
I'm definitely going to data log before drilling the BBK 58mm throttle body any more. My 383 idles fine (1100rpms) until I give throttle input and only does this after the car sits for a few days/weeks. After the 383 has been warmed up and restarted, it usually idles fine; it is only ever on the initial start up after sitting for a while 😵💫. It has been an issue that has been driving me crazy because it is intermittent.
I have an update. I've been driving the 383 for the past few weeks on and off; the idle issue has only appeared 1x since drilling a 1/8" hole. This is a noticeable difference from before the hole.
Below are the IAC counts from a data log. They ranged between 90-100 (95 in picture). Im going to drill a little bit bigger hole and test again; I think I am shooting for counts in the 35-40 range. I think it is on the right track though!
You can slot the screw holes on the TPS to "rotate" it to get the volts right. IMHO kinda a hack way of doing it
Best to dill the size hole you need but take BABY steps as 1/64 bigger makes a good drop in !AC counts. IIRC mine is 11/64 on my 383 but my TB is a stock rebore to 52. Never drill without being able to monitor IAC counts at each step
I appreciate that! Im going to do a 9/64" hole next, then Im gonna data log again. I just havent had time and the weather has been junk lately. Im working it in baby steps; the 1/8" hole helped a lot so far! I don't think I need much more.
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383 LT1 Idle Issue 
lmao). See pictures below:
