IAC issue on 87 K5 350

[04401k5]

This truck has an idle problem but no check engine light comes on, haven't checked for codes yet. I've changed many parts trying to isolate the problem and the only thing that I've found that makes any difference is to unplug the IAC wich causes a high but stable idle and it runs great when you rev it up. Plug the thing back in and it runs like crap. I don't want to spend the cash on a new IAC unless I have to. Can I run the truck with the IAC unplugged and bring the idle down by adjusting the trottle stop? Any help would be great.

 

[bp71k5]

This truck has an idle problem but no check engine light comes on, haven't checked for codes yet. I've changed many parts trying to isolate the problem and the only thing that I've found that makes any difference is to unplug the IAC wich causes a high but stable idle and it runs great when you rev it up. Plug the thing back in and it runs like crap. I don't want to spend the cash on a new IAC unless I have to. Can I run the truck with the IAC unplugged and bring the idle down by adjusting the trottle stop? Any help would be great.

The fuel injection section might be a beter place to ask this, but the iac is what controls the idle speed. It might be dirty or stuck. Try removing it, cleaning, and then resetting it before buying a new one. Do a search for the reset process since it's kinda confusing.

 

[04401k5]

can't post in the injection section so I put this here, just wondering if I can drive around with the IAC unplugged, I'll give a reset a try, thanks

 

[bp71k5]

can't post in the injection section so I put this here, just wondering if I can drive around with the IAC unplugged, I'll give a reset a try, thanks

The bore for the iac plunger may just be clogged. You need to jumper the aldl connector and remove the cable after the plunger has shut. Then you can remove the iac and clean any junk out of the hole. I forget the exact process.

 

[thatK30guy]

My '91 K5 ran like crap at idle for a long time. It would level out when I revved up the motor. For a while, I thought it was the IAC, too.

Turns out it was the fuel pump. A new one did the trick. The old one was putting out like 5 psi when it should be 7 or 9 (can't remember which).

 

[zombie1969]

My '91 K5 ran like crap at idle for a long time. It would level out when I revved up the motor. For a while, I thought it was the IAC, too.

Turns out it was the fuel pump. A new one did the trick. The old one was putting out like 5 psi when it should be 7 or 9 (can't remember which).

9-13 is the operating range.
Cleaning the throtle body is easy and cheep to do so thats you best place to start.Unplug the valve before removing it or you risk damaging it.Dont use metal or sharp objects to clean the body.A tooth brush works good with carb clean.

 

[04401k5]

Pump, tank, filter, fuel lines are all new, new plugs and wires, no vacuum leaks, everything is working and plugged in, truck has plenty of power and runs strong but it would not idle.

IAC port and pintle is clean and I did a reset on the IAC, it is working. Still would not idle. So I decided to do what they say not to do... I removed the plug over the adjustment screw on the TB to bring up the idle but first I placed an indicator on the throttle arm and set the dial to zero so I had the ability to bring it back to the factory setting. I backed out the screw so I could measure how far the arm moved down to the fully closed position but it did not move down at all. So there is probably some carbon build up that is keeping it from closing all the way or the screw might have backed out over time, I don't know. I then adjusted the screw so I could get an idle set and now all is good.

Right now I only need this truck to plow but I plan on fixing it up as time goes on. I just replaced the floor in it and I have one of the few rust-free K5's in Maine so its worth it go for a full rebuild. Just a matter of time.

Any way... that's what I did to fix it, not the correct process but I will go through the thing 100% some day. Thanks for the help.