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KMP1171, ASE Certified Technician
Category: Chevy
Satisfied Customers: 224
Experience:  Mech for 20yrs and GM Specific for 15
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How do I adjust the Idle up on a 1989 Chevy pickup TBI I t

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How do I adjust the Idle up on a 1989 Chevy pickup TBI? I t runs so good now that the idle is a little low,If i can ajust it up a little it will be fine.I know that might not sound right but it runs really well,just need to get the Idle up.


The engine idle speed is controlled by the ECM through the Idle Air Control (IAC) valve mounted on the throttle body. The ECM sends voltage pulses to the IAC motor causing the IAC motor shaft and pintle to move in or out a given distance (number of steps) for each pulse, (called counts).

This movement controls air flow around the throttle plate, which in turn, controls engine idle speed, either cold or hot. IAC valve pintle position counts can be seen using a scan tool. Zero counts corresponds to a fully closed passage, while 140 or more counts (depending on the application) corresponds to full flow.

The IAC valve can be on the throttle body, usually next to the throttle position sensor

The IAC valve can be on the throttle body, usually next to the throttle position sensor

Customer: replied 7 years ago.
Hi,Thanks for that info,But can I adjust it by hand or do I have to take it somewhere and let them do it...If it were a Carb just turn a screw,but how do I do it,you see what im trying to say?
UNfortunately it isnt adjustable. But have you checked for Vaccum leaks and have a injector cleaning done with a good Throttle body cleaning. Check air filter 2 may solve issue.
Customer: replied 7 years ago.
Okay,becuase i added headers,all new exhust,E3 plugs,Accel wires,cap rotor,msd coil..I can upgrade to a 25%better flow TBI and be able to adjust the fuel pressure up from stock 11psi to like 13-14 then that should boost her up and more power.That way I think it will Compement the upgrades.would you say Maybe..this is my lat Question,but thats what i want to do next for it..
To change what you are wanting to change. You need to buy the computer E-PROM chip and replace .
Customer: replied 7 years ago.
One More Sorry! Where would I get that? E-PROM CHIP Thing....I tried a Jet chip and it didnt work at all,just worse..but what ever it takes i guess to make more power and all..
Another expert just offered this.
Most aftermarket Perfomance parts places can order

Maybe there is a throttle plate adjusting screw(20 torx) at the front of the TBI unit? Has a aluminum removable cap?
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Customer: replied 7 years ago.
Okay,I will look at it again to see if it has that.....THANKS For youre Help..
let me know
Customer: replied 7 years ago.
I will look at it tommorow,thanks 4 youre help,CYA..