: Minimum idle speed adjustment on 1996 throttle body

03-15-11, 10:39 PM
How does one perform the correct minimum idle speed procedure on the 1996-1999 throttle body to obtain the proper idle rpm?

I'm unable to find this information in my GM Eldorado service manual.

I have a stock throttle body that I'm trying to get in the correct position after messing with it trying to get my car to run.

Would it work to disconnect and take out the IAC or ISC motor and plug the hole....Then adjust the throttle body screw until the car idles at a or "the" minimum idle rpm at 550rpms? By the way, is 550rpms correct?

After figuring out the correct procedure, I would then do an idle relearn procedure on the car with the IAC/ISC in operation.

Any thoughts?

03-15-11, 10:54 PM
The PCM controls idle speed. You cannot adjust it. Idle speed is 650 RPM. If the IAC valve is bad, it should set a DTC. Have you cleaned the TB?

03-16-11, 12:56 AM
Thanks Ranger.

I'm running one of AJ's tunes with the LS1 style computer and mild 272 cams and it won't run right. We've gone through at least 6 different tunes with no success.

I'm trying one last time to get this to run before I jump ship and go aftermarket. I've altered the stock throttle body setting and want to start from scratch with the stock idle settings. I'm double checking everything in the idle system.

My problem is that it stalls when I come to a stop sign or light. I've found no vacuum leaks by using propane. All my sensors are new except the cam sensor. Just cleaned the MAF sensor this evening with brake cleaner. Will be replacing the PVC valve on thursday.

I'll try to set it at 650 RPMs without the ISC and then do an idle relearn, I guess. Shoot. I'm at my wits end. Has new head gaskets and the heads were done at my local shop that said they were cherry nice.

03-16-11, 12:59 AM
Sorry. Yes, I do have a very clean throttle body with no carbon build up or on the ISC pintle.

03-16-11, 03:32 PM
I'm running one of AJ's tunes
Ahh, you didn't tell us that at first. That puts a whole different spin on things. Like I said, the PCM controls idle speed. You probably should be talking to AJ.

03-16-11, 03:53 PM
I'm running one of AJ's tunes with the LS1 style computer and mild 272 cams and it won't run right. We've gone through at least 6 different tunes with no success

This setup has nothing to do with 99.9% of the FWD Northstar drivetrains in here - the idle and cutoff problem needs to be worked out with the tuner/designer.

03-17-11, 11:24 AM
A-OK. Thanks.
AJ has been stumped as well.

03-17-11, 04:44 PM
throttle body screw? you mention adjusting it so i assume you have one. as do i? since i have a 96 as well. never looked for it since i have never had an idle issue. lift foot off gas. throttle blade closes. iac controls idle speed. sitting still or driving down the road. seems to me pcm controls iac.

03-17-11, 09:46 PM
Yes, the throttle body screw. It is set at the factory.

I don't know what that factory setting is...as I have altered the stock screw/butterfly plate position in conjunction with an idle speed relearn to try to stop it from stalling at a light or stop sign. The stock setting seems to be close to all the way closed just beyond the binding that occurs when its completely closed without the screw holding any position.

03-18-11, 10:34 AM
you cleaned bore. binding could be caused by worn shaft bushings. i had other GM car that would always die on hot restarts. cleaned throttle bore and issue went away. maybe source a used throttlebody? i bought a used intake. seller asked if i wanted throttle body also. did not need it so i got only nylon portion of intake. who needs extra parts.