idle problem

[al david]

Hi there, I am having a idle problem after the truck is at full running temp at stops. The idle drops very low, I have changed most every thing posable here is some things i've replaced and repaired, first it needed valve seals in order to pass smog, intake gasket replaced, timing set at 4, changed rotor, cap and module, spark plugs, wires, rebuild throttle body carb, replace the idle control sensor, replace the throttle control sensor, replaced the co2 sensor, replace the ignition coil, cleaned and checked the egr valve, I took the truck to a shop and they did a propane vacuum leak check, they could not find the problem as there was no leak detected. There is a thing at the back near the distributor it looks like a vacuum block with a wire plugged into it, I don't know what it is called and wonder if this could solve the problem, sorry I wish I knew what it's called hopefully you understand what I am trying to identify. Thanks for the help as I am out of sorts. Also I noticed the Idle goes low after I put the transmission in gear and during stops and off the freeway.

 

[thinger2]

What year, what model, which engine and transmission.
Always start with that info.
If you can post a picture that would help too

 

[Nad_Yvalhosert]

How low is your definition of low?
What year, model, engine size, transmission, A/C on or off?

 

[al david]

What year, what model, which engine and transmission.
Always start with that info.
If you can post a picture that would help too

Darn it, I am so stressed out that I left out that information thank's for your help, it is a 1988 silverado truck c1500 not sure about trans but may be 700r4 ,operating at full temp and ac off.

 

[al david]

How low is your definition of low?
What year, model, engine size, transmission, A/C on or off?

The idle drops and fluctuates from 539 to 499 and feels like it wants to stall. This is a 1988 silverado c1500 truck with a 700r4 trans and I have not turned on the a/c due to the fact that it is not working, the wire connector is broken.

 

[Nad_Yvalhosert]

The item you're referring to by the distributor is an oil pressure sensor. Nothing to do with idle.

 

[Nad_Yvalhosert]

There are a few things.
Start with a scan tool, and check your TPS voltage at key on, engine off. Should be .5V. Adjust TPS if its not.

Next, engine running, A/C off, tranny in park, check the the throttle linkage. Make sure the throttle blades are actually closed.

Third, there is an idle adjustment process. Start with knocking out the aluminum cover over the idle screw. It's a small disc, about a 1/4" round.

Fourth, you need to extend and unplug the IAC. Theres a listed procedure, starts with jumpering a couple pins in the DLC, I forget which ones. Once the IAC is fully extended, unplug it to keep it closed. It will set a check engine code, but you can clear it later.
Now that the air bypass ducts are closed in the throttle body, you start the engine and screw in the idle screw until you get the RPMS at your desired level.

Lastly, shut off the engine, plug in the IAC, unplug the battery, step on the brake pedal, reconnect the battery and fire up the truck.

Ought to be running at normal IDLE speed now. Best of luck!

 

[Nad_Yvalhosert]

Also, a vacuum leak will cause a fast idle.

 

[Erik the Awful]

Third, there is an idle adjustment process. Start with knocking out the aluminum cover over the idle screw. It's a small disc, about a 1/4" round.

DON'T TOUCH IT! Fix what's wrong.

 

[Hipster]

as per factory spec they idle 500-550 rpm, if it wants to stall at that rpm something else is up.

Has the timing been properly set?