Help,please! Possible IAC failure.

[RustedRanger]

I have an 87 4x4 2.9,so far since I got it last month I have replaced the following:gas tank,fuel filter,gas cap,O2 sensor,CTS,hoses,radiator,front brakes,air filter,exhaust,plugs and today the dist.cap and rotor and plug wires. I set the TPS and the lowest I could get is was .96V. I kept having a problem with the idle bouncing around and running rich at idle when hot. I have it running MUCH better than when I started BUT.....today I changed the dist. cap,rotor and wires. After that I found out my Uncles timing light didn't work. So I drove it to Autozone to see if they "loaned" timing lights but they didn't so I drove back to the shop and decided to clean the AIC valve to see if it would help the idle since I'd have to drive it 30 miles to use my Dads timing light. I took it off and it's the original (147,100 mi.) and cleaned it with what throttle body cleaner I had left(not much) and sprayed out the ports with carb cleaner. I started it and it runs horrible! Like a V-4! I tried moving the dist again with no change,I took the valve back off and put a little permatex on the gasket and blew it out with the air hose and still no change. Did I hurt it with the compressed air? The only other thing I did after driving it to Autozone was wire tied the wires down and routed them carefully. The engine still dies if I unplug the AIC with it running but it runs like it has a huge vacume leak and I checked all the hoses and lines. I double checked all the plug wires and they are all on. Can a bad or failed AIC valve cause it to run this bad? Thanks for the help.

 

[Earl43P]

If the idle changes (dies in your case) when you disconnect the IAC connector, it is working. I'd look elsewhere. Go after the plug wires, suspecting either a bad one (or two), connected to wrong cylinder, or pinched and grounding out. Sometimes you can see them arc if you mist with water, at night. I'd try that. They ARE the last thing you touched....other than the IAC.

 

[RustedRanger]

But it ran fine when I drove it to the parts store. I triple checked that they are all on all the way and none are touching metal and they are all seperated. But it is dark now so I will take a look to see if I see any arcs. Thanks

 

[Earl43P]

"The only other thing I did after driving it to Autozone was wire tied the wires down and routed them carefully."

I'm just going by what you said. Last thing you touched. I don't know what you mean by tied them down. They make plastic looms that keep the wires seperated. If you have plug wires grouped together and touching each other, that'd be your problem.

 

[IMenriched]

Have you tried to get codes..might be unrealated to what you've done so far.
http://www.therangerstation.com/tech_library/OBD_I.html

double check those grounds...and connections

 

[RustedRanger]

I checked and the ground straps are intact,all the plugs are plugged in. I used plastic wire/zip ties to sepperate and locate the plug wires.

 

[RustedRanger]

One thing I didn't mention was that I moved the main wiring harness around some. There is some white powder in the plastic loom. Could it be corrosion? Happy Resurection Day!

 

[IMenriched]

One thing I didn't mention was that I moved the main wiring harness around some. There is some white powder in the plastic loom. Could it be corrosion? Happy Resurection Day!

Hard to say what the white powder is ...suspect dried up adheasive from some tape somewhere. But wouldn't rule out corrosion either...that generally happens on connections or where insulation is worn thru.

 

[CraigK]

I've asked this before . . .

Just what does the IAC do????
Controls what air?
It doesn't (???) control exhaust recycle, as that's the EGR and associated system, right?

CraigK

 

[Tedybear]

IAC: Idle Air Control Motor

It controls air flow into the intake when the throttle plates are closed. If you look at one when removed you'll see it's two sections, and has a rod in the center, with a tapered part separating the two "sections". The first section is routed to a port just in front of the throttle plates, and the 2nd (rear) section is ported right into the intake behind the throttle plates.

The computer controls how much that tapered section is pulled back/open to allow air flow. The more it's opened? The more air flow gets into the engine. (the computer does this, and at the same time regulates the fuel flow from the injectors) It's a lot more accurate then the older systems that used choke plates and fixed ports to regulate idle with the carb systems.

S-

 

[CraigK]

Thank you tedybear.
Makes sense.
Additional questions ... (if anyone knows)

Does the IAC "motor" just receive and respond to a computer signal (i.e. open this much), or does it also provide electronic feedback?
If unplugged, the engine idles very poorly. Is that because the IAC then full opens or full closes, or because a circuit is broken that signals the computer?
If the IAC was blocked off (blank gasket), what would the effect likely be?
Just wondering, given that erratic idle seems very common.

CraigK

 

[RustedRanger]

After thinking about it I think I killed the plugs when I cleaned out the ports for the IAC. The wires are fine under the loom except a small hole in one wire and I fixed that. One of the first things I did when I got it was put in Bosch Plat +2's and then read here that they foul easily in 2.9L's. I ran a few weeks not knowing the thermostat was stuck open and I think washing all the junk from the IAC ports down in the engine did them in. I got the stock plugs today and hope to put them in tomorrow. I remembered a vacume leak would cause it to run lean,not super rich like it is now. I does act like fouled plugs. Actually the idle has been more steady its just that it runs really BAD! I'm just hoping and praying the plugs fix the main problem. A good way to explain the way it runs is like when you spay out a carb or throttle body and when you restart it and it runs really bad till it clears out except it didn't clear out. I already had sprayed out the throttle body when I first got it but not much reaches the runners since its at a downward angle. I really think/hope I killed the plugs not anything else LOL

 

[CraigK]

If the plugs are not your problem.
Is it possible you damaged the O2 sensor with the carb cleaner you used on the IAC? (Even if the O2 sensor was new.) Quick/Easy test - disconnect the O2 sensor and if your problem gets better, it's a clue the problem may be the O2 sensor.

Also, I found that throttle/carb cleaner will dissolve and melt some rubber-like vacuum hoses. Carefully check again for vacuum leaks and leaking connectors/gaskets.

CraigK