Delete IAC in 2002 QX4

[FX4OFFROAD]

Dear forum members this is my second post to the forum. I hope I am doing things right. I really appreciate the help.

I have the P0505 code and I have replaced the IAC no change. I removed the ECM and the board is not burnt. If I unplug the IAC and take the throttle cable that controls cruise control it will run without surging. Is it okay to do this? will it cause damage? can I delete the IAC somehow? the relearn process didn't work for me. I would just like to be able to drive around the farm without it surging but not cause any damage.

thanks for the help.

AJ

[EdBwoy]

Hello and welcome to the forum. I hope someone who has actually done it comes and gives you direct advice.

If I may ask, what brand of IACV are you using?
Are you in a position to take it to a dealer for programming? - I might already have the answer to this, considering it's a farm truck. Hehe

Also, I wasn't clear of what you did with the cruise control wire. Did you pretty much manually operate the throttle plate? Because either the cruise control, gas pedal or that circular bracket will achieve the same function.
So here I needed clarification on what you said. Because when throttle is applied the IACV doesn't have a use and it will smooth out. When you (or the cruise control genie) have your foot off the pedal, the TPS (throttle position sensor) relays this back and asks the IAC system to take over and keep the engine running at whatever the idle spec is.
I am thinking you'll still need it hooked up.

Are you using the relearn procedure outlined on page 70 of the FSM's EC section?

[FX4OFFROAD]

Thanks for the reply Ed,

I am using a HITACHI IAC. The valve only seems to push out and therefore appears to remain permanently stuck closed. There are two throttle cables that I am aware of, one is connected directly to the pedal and the other seems to be actuated by the truck which is the one I have removed. Removing that one seems to take control away from the computer which I assume is trying to compensate for the IAC being stuck closed and causing the surge. I hope I am understanding that correctly. I have never worked with a vehicle quite as complex as the QX4. I followed the instructions in the EC manual but it did not seem to work. You guessed right about taking it to a dealer, I suppose I could trailer it there if it was the only way to get it to run.

Thank you for your consideration,

AJ

[FX4OFFROAD]

Could the TPS be faulty and cause the IAC to stay in the closed position?

[EdBwoy]

OK, as I recall - on the intake manifold, the throttle cable and snakes back around over the intake and into the firewall then to the gas pedal. The other cable is your cruise control, and I believe is vacuum actuated to maintain cruise.

You disconnected this one and the engine seemed to smooth out, correct?
First, I didn't think this system came into play at all during idling, as the manual throttle body doesn't compensate for idle - it merely relays the position of the plate.


What is the backstory - did the code P0505 pop out of the blue or did something else trigger these events?

Anyway, if disconnecting just that one cable smooths out the idle, maybe you have a sticky throttle. I would advice you to use some throttle body cleaner and make sure the throttle chamber and plate are reasonably clean.

[FX4OFFROAD]

The engine began to surge as i was driving it home from the seller, the seller had convinced me that a bad battery was to blame for its hard starting and no check engine light was on. Once the surging began i decided to plug in a scan tool and was horrified to find a laundry list of codes, as it turns out they had removed the check engine light bulb and knew that once it warmed up it would surge/maintain an idle over 1000rpm. the reason it starts poorly is that the IAC is stuck shut, if you take the IAC out and cycle the key repeatedly on and off it will push itself out and out and out until the mechanism falls apart, it never retracts like its supposed to. (even with the new IAC.) I don't know a lot about IAC valves so i pulled one out of a jimmy i have on the yard and cycled the key as a comparison, it moves out with key on and retracts with key off.

It shows a code for
P0031 Heater control circuit bank 1 low
P1140 intake valve timing control position sensor bank one
P0328 knock position sensor high voltage
P0505 Idle air control generic

Thanks for the advice,

AJ

[EdBwoy]

Ahhh, I see now. Potentially dishonest sellers.
Here is something I have said and will keep posting in as many relevant threads as possible:

...
Then, without encouraging anything unethical, I'll say that I know the CEL has a replaceable bulb.

*I'll also add that when buying a used vehicle advertised as having "no dash lights on", in addition to running the code reader, I still turn the key to the ACC then ON positions and observe to ensure all lights including the CEL illuminate briefly.

Back onto the idle issues. I have honestly never even thought of seeing its behavior with the key on or off. Just to rule out that the ECM is keeping it stuck as intended, could you use the battery as well to see if it still won't retract?
This is me guessing, and you know, some actuators are programmed to respond in one direction because something else reverses their direction outside of the electrical circuit... for example a spring that keeps something closed when current isn't applied any more.
It would be nice to know what the previous owners had done to troubleshoot the issue. Because I'd like to assume that they did try a lot of things before resorting to remove the bulb.


On another angle, can you check the 4 12/10mm nuts that are used to adjust the throttle cables? Do both sets of nuts have yellow or white paint marks facing up? That is the assembly mark to show the the throttle plate has been set to the right idle spot. I ask this to see if someone tried to alter the idle by tightening the cable a little.

Still, I encourage you to check and clean the throttle body. If it is gunked up, this could help.


On the other codes:
Knock sensor, if I recall is usually a ghost code that only shows up when other codes come up. I wouldn't worry about that one just yet.
The IVT code. Do the standard harness connection check. If it is snug and the pins aren't corroded or anything, check the oil level and cleanliness. It could be gunked up - removing it to cleant it wasn't too hard IIRC, but I also remember having to replace one.

[sroberts]

If you have not done so already I suggest checking the IACV resistances with an ohmmeter to make sure they are in spec per the manual. There's a thread on here somewhere about that. I had the same issue and found that one of the 4 values was way out of spec, even though the IACV was only a few months old.