Adjust the idle on the 3800sc externally (without reprogramming the PCM). (Page 1/1)
RotrexFiero OCT 29, 04:06 PM
Is there a way to adjust the idle, I'm running a little high around 1100-1200, rather than 800rpm.

Its been this way since I ported and upgraded my pulley (3.5).

[This message has been edited by RotrexFiero (edited 10-29-2021).]

olejoedad OCT 29, 04:17 PM
Have you checked for a vacuum leak? Blower to LIM is a common place for that.
RotrexFiero OCT 29, 06:01 PM
I'll double check.

I did check all the vacuum lines.

I've been dealing with this for some time. I upgraded the pulley at the same time I had the intake ported.

I never had the PCM reprogrammed, but I was told that would not be necessary.
olejoedad OCT 29, 08:34 PM
Showing any error codes?

Reprogramming the PCM is a good idea for optimum results....
Dennis LaGrua OCT 29, 10:12 PM
The 3.5" pulley is just a slight downsize so I can't see that affecting the idle. The supercharger doesn't put out any boost at idle. Many Grand Prix owners back in the day ran perfectly OK with pulleys as small as 3.4" with only an improved exhaust and cooler plugs. However, porting may change the amount of air that the engine will intake so you might have to adjust the MAF sensor values ( fueling vs air flow) in the program. That will adjust the fueling but not sure about the idle speed.
Before you do anything I would insure that you have no vacuum leaks. To answer the question directly there is no way to adjust the idle speed outside of changing it in the PCM. I would recommend that you purchase the HP Tuners Tuning & Editing suite. Changes on OBDII PCM's are not hard to do and the Grand Prix unit is very easy to work with. I'll open up the HP Tuners Editor later on and take a look at what could be adjusted
RotrexFiero OCT 30, 06:31 AM
Hi Dennis, nice to hear from you!!!!

Yeah, I'm thinking this ported intake is the culprit. I wish it was as simple as a vacuum leak.

I am getting a code. High Idle. Cant remember the code number.

I heard from fastfieros and he wanted around 135 to reprogram. But, is there a precedent for this type of modification? I'm into voodoo engine modifications?

If not I am thinking of going back to a OEM intake.

I must say the ported one lacks the punch of the OEM but does flow better at higher RPMs. I could live with either.