4.0 swap - High Idle Still

[lilfordrunner]

Long story short, a 93 4.0 is now in an 87 ranger and the idle is at 2k.

So, I checked the MAF, its clean and properly functioning.

I checked the IAC, when I take the IAC off and tape up the holes the truck idles 800 during ice cold start up. With the IAC on and connected it idles at 17-2200 erratically during ice cold start up. Once the engine warms up, the truck will die and the will not start until temperature is back to cold, whether the IAC is connected or not.

Second part of the equation, The o2 sensor is connected to the truck harness as it was originally, but the ENGINE harness that came with the 4.0 has two connectors for two o2 sensors. Do I need to hook anything to those, or will it make a difference since the o2 sensor is in fact connected elsewhere.

Could really use any help out there. This thing is on the verge of hitting the road; its been too long!!

 

[90jurassic2]

Does it idle down when you put it into gear?

 

[lilfordrunner]

Yes it does

 

[PanamaExpat]

Sure you got all the vacuum plumbing hooked up correctly? Also I ma curious as to why you didn't switch the y pipe over to the dual O2 sensor one from the donor vehicle?

 

[kimcrwbr1]

I would think you need to connect all the sensors the computer is looking for all the inputs. Did you try reving the engine up to around 2000 rpm and then unplug the IAC. See if that allows it to idle it should close the IAC when your using the foot feed. Maybe the throttle butterfly is open too far at idle if it idles good with the IAC disabled and closed. While it is idleing close the throttle butterfly until the engine stalls and plug the IAC back in turn the key off and the iac should open. then start it and see how well it idles. Check for vacuum leaks using a piece of vacuum tubing stick one end up to your ear and search around with the other end at all the gaskets and fittings the closer to the leak the louder it will hiss. If you stick it in the throttle body you will know what to listen for. It works good for isolating exhaust leaks also.

 

[kimcrwbr1]

My exhaust guy has a piece of vacuum tubing taped to a soft wire that can reach hard to get at places so you dont burn yourself just a side note.