What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

88 TBI idle help wanted!!!

firemedicsafd

firemedicsafd

Professional Murphy magnet
 Premium
Joined
Jan 23, 2005
Posts
565
Reaction score
50
Location
St Augustine, Florida
I have an 88 K5 Blazer TBI 350/700r4 combo. She will not idle correctly. During the morning, she will start fine, idle at about 1000 to 1200 in park AND in drive, and run good. As she warms up, the idle drops off to the point where i have to keep my foot resting on the pedal to keep it running and it runs rough. But once i get going, she smoothes out and runs good again. All my sensors are new...replaced at least 2 times each. I USED to get the ESC code but once i removed my TBI spacer and got my TV cable back to normal...that code has NOT resurfaced. Sombody PLEASE help me!!!
 
You need to read up on how to check base idle and or adjust if needed.
 
Now that i have time i can explain how to do this.

First you need to jump the A and B terminals in the ALDL connector (the 2 upper right terminals) then turn the key to the ON position (key ON engine OFF) and wait for 30 seconds, leave the key ON and now climb under the hood and remove the connector from the IAC motor (Idle Air Control), now go back to the ALDL connector and remove the jumper and start the engine. Look at the driver side of the TBI unit and locate the "plug" that covers the Base idle screw and if it is still there you need to carefully pry it out and discard it. With the engine running and the trans in gear you now need to adjust that screw so that you achieve 550rpm. Once you've done that turn the engine off and reconnect the IAC wire and restart the engine. What you've just done is set base idle and now the IAC controls idle as it should. If you still have an incorrect idle then you need to be looking for a vacuum leak somewhere.
 
BlackBourbon said:
Any way to do this without a tach?:o
Click to expand...

It will be hard to set the idle speed without a tach unless you mark the pulley and can count REALLY FAST. :D

Sounds like it's either time to buy some new "toys" (tools) or pay someone to do this for you. I would rather buy tools than pay anyone to work on my stuff. If you don't know how to do something there are plenty of us here that can guide you through it if you have the tools required.
 
This must be why I have high idle all the time after swapping the 700 to 465.
 
Cool info! mine idles at approx 750 when warm...

Rene
 
4X4HIGH said:
It will be hard to set the idle speed without a tach unless you mark the pulley and can count REALLY FAST. :D

Sounds like it's either time to buy some new "toys" (tools) or pay someone to do this for you. I would rather buy tools than pay anyone to work on my stuff. If you don't know how to do something there are plenty of us here that can guide you through it if you have the tools required.
Click to expand...


haha that's kinda the answer I was expecting. I was shooting in the dark incase there was a way to reset it back to some factory "preset".

I have a tach in my car I can rob for a minute to do this.

And I couldn't agree more about other people working on my stuff.
 
I wonder what the IAC steps are? Wonder if the IAC changes steps? Maybe a scanner would help out? I'd use a scanner to check the IAC before making any changes to the throttle blade angle. Maybe the IAC needs a good cleaning? Maybe the IAC is not changing steps because the IAC is stuck in one position because of carbon build up?

It's not easy to figure out TBI problems without a few special tools!:mad:

There is the option of programming different IAC steps with TunerCats. The IAC has a park position and a park neutral offset parameter.

dave

IAC.jpg
 
THUNDERUSONE said:
What and where is the ALDL connector?
Click to expand...

ALDL stands for (Assembly Line Diagnostic Link) and is used to attach a scanner to figure out where to start looking for a problem should you get a SES (Service Engine Soon) light come on. Like was said it is located under the dash on the driver side down near where your knee would be.

Here is what the ALDL connector looks like.

ALDL connector.jpg
 
4X4HIGH said:
ALDL stands for (Assembly Line Diagnostic Link) and is used to attach a scanner to figure out where to start looking for a problem should you get a SES (Service Engine Soon) light come on. Like was said it is located under the dash on the driver side down near where your knee would be.

Here is what the ALDL connector looks like.
Click to expand...

I thought that was it. I have been out of these trucks for a while and I bought a 91 burb over xmas. Thanks for the clarification.
 
4X4HIGH said:
Now that i have time i can explain how to do this.

First you need to jump the A and B terminals in the ALDL connector (the 2 upper right terminals) then turn the key to the ON position (key ON engine OFF) and wait for 30 seconds, leave the key ON and now climb under the hood and remove the connector from the IAC motor (Idle Air Control), now go back to the ALDL connector and remove the jumper and start the engine. Look at the driver side of the TBI unit and locate the "plug" that covers the Base idle screw and if it is still there you need to carefully pry it out and discard it. With the engine running and the trans in gear you now need to adjust that screw so that you achieve 550rpm. Once you've done that turn the engine off and reconnect the IAC wire and restart the engine. What you've just done is set base idle and now the IAC controls idle as it should. If you still have an incorrect idle then you need to be looking for a vacuum leak somewhere.
Click to expand...

Ok, i followed your instructions on the base idleadjustment . it all worked correctly until i reconnected the IAC connector again and restarted the engine. Now it idles at 1000 in park. When i put it in gear it drops down and then revves back up to about 1100, then when i put it back in park, it jumps to 2000 then slowly drops back down to about 1100. but it takes about a minute to do that. I have replaced the IAC twice before i posted, checked all vacuum lines, they are fine, AND even replaced the ECM with another one i had. Everything stays the same. Isnt there some kind of adjustment on the IAc itself? PLease help me....i have to work tommorrow and i would like it to run properly. Thank you!
 
Have you disconnected the throttle cable from the TBI unit? Alot of times the TBI body gets wore out where the throttle shaft goes through it and makes the throttle sticky. Try disconnecting the throttle cable and then start the engine and physically pull back on the throttle lever to make sure the throttle is fully closed. If you can make the RPM's go down you have a wore out TBI unit and will need to get it rebushed (shouldn't really say RE-bushed as they don't have bushings from the factory but i think you know what i mean).

There is no physical adjustment for the IAC motor, that is the job of the ECM (IAC counts).
 
You must log in or register to reply here.

Latest Posts

Top Bottom