TBI adjustment...??

[jpaitala]

Newbie want's to say hi to everyone!!!

How can I adjust the idle speed in my '89 Blazer(350).
Everytime when I shift to neutral(manual tranny) the idle speed jumps 500RPM upwards... This doesn't sound nice. The normal idle is a bit high, about 1000RPM. Can this be adjusted to ~750-800??

Thanks.

 

[azblazor]

Welcome to ck5! If your idle is high it is probably a problem with some part of the system. There is an idle adjustment on the drivers side of the throttle body unit, but it has a cover over the adjustment screw that must be removed. I would recommend scanning the computer for codes and proceeding from there (before trying to adjust the idle). Do you have factory service manual? They are very good for troubleshooting problems like this.

 

[HarryH3]

The computer controls the idle speed by regulating how much air is allowed to bleed around the throttle plates. It does this by moving a pintle in and out of the air bleed circuit, using the Idle Air Control (IAC) motor. However, if there is a vacuum leak somewhere else, then so much air will come in via the leak that even when the IAC pushes the pintle all the way closed the idle speed is still too high. Check all vacuum lines and connections for a leak before you start changing other things. /forums/images/graemlins/cool.gif

 

[jpaitala]

There was a minor vacuum leak, fixing that helped a little but the idle is still a bit high...

I can't get service manual in here(Finland). Could someone get a manual and send it to me, I can pay it through paypal?!

 

[azblazor]

There are GM service manuals on Ebay alot, give them a try.

 

[80 Chevy K20 4x4]

I've had to replace a worn and leaking TBI base plate gasket before on TBI motors and they made the engine idle extremely high. You might spray some carb cleaner around the base of the TBI to see if it changes the rpm any, if it does replace the gasket.