2003 DF90 - Issue with idle air controller

[Lowery99]

Just finished rebuilding this engine. Runs like a top above idle. It will idle and stay running, but sounds starved for air and is just rough.

Figured something with the IAC. Bought a used one, no change. I do not see my old one or the new (used) one opening or moving at all when the key is turned on or when the engine is running (I left one on the engine, plugged the other into the loose IAC).

Neutral switch is triggered. IAC has a steady 12.7v running to it. On either of them, if I plug them in I can feel slight vibration, like a small motor running, but no movement at all on the IAC. Tested the resistance on the IAC leads and get 10 ohms.

Also verified the engine purrs like a kitten at idle if I loosen the IAC and allow a slight bit of air through. With the IAC tight, if I put my finger on the black IAC hose opening I can feel a very slight amount of suction.

Does this sound like bad luck to get a second bad IAC, or can anything else be at fault?

[catacom225]

Sounds like you may have to go through the RESET Air Idle procedure

[Lowery99]

Sounds like you may have to go through the RESET Air Idle procedure

I haven't been able to. I can get the engine above 1000 idle for 10 seconds, but the beep never comes to say it has gone into that mode.

[catacom225]

Dumb question but Can you confirm the buzzer is working , Engine warmed up and throttle closed. Using the bypass screw raise revs to >1000 for >10 secs. This will set the IAC system to a fixed value, Duty mode and set off the caution buzzer - 0.5 sec tone every 3 seconds, for 5 mins. Set the idle speed during this time to 625 plus minu 25 rpm using the bypass bleed screw.

[Lowery99]

Dumb question but Can you confirm the buzzer is working , Engine warmed up and throttle closed. Using the bypass screw raise revs to >1000 for >10 secs. This will set the IAC system to a fixed value, Duty mode and set off the caution buzzer - 0.5 sec tone every 3 seconds, for 5 mins. Set the idle speed during this time to 625 plus minu 25 rpm using the bypass bleed screw.

Yeah, buzzer is working. I put an aftermarket buzzer on and I am getting a 3-2 code (I think because the engine is starved for air) and the warning from that is deafening.

[redlowrey]

You are on your second iac valve and your second map sensor and you still have the same problem. I told you a month ago you have low manifold vacuum and a high map signal voltage that won't shift off 2 volts which should be 1 volt at idle, why the 3.2 code.

Fix that problem and everything else will fall into place, and checking the timing means jack shit in relation to where the camshaft timing is, it will switch the transistor off based on information from the crank sensor.

[Lowery99]

You are on your second iac valve and your second map sensor and you still have the same problem. I told you a month ago you have low manifold vacuum and a high map signal voltage that won't shift off 2 volts which should be 1 volt at idle, why the 3.2 code.

Fix that problem and everything else will fall into place, and checking the timing means jack shit in relation to where the camshaft timing is, it will switch the transistor off based on information from the crank sensor.

When I was checking that issue it was the entire rpm band was all over the place, ran poor at all rpm, sometimes would idle sometimes not.... we found replacing the plugs solved 99% of it, one of them was grounding out. I have multiple hours on the lake with it now, perfect performance everywhere but idle. And, I am working on the idea that if the iac is not opening, not enough air is getting in and causing low vacuum. Just tested the duty load last night and seeing 50% + with 12.7v like the engine is trying to demand more air but no movement on the iac. Also the fact that manually opening some air to bypass the iac (loosening it) it idles perfect at the 650 rpm. To get it to 650 with the iac tight, the adjustment screw has to be almost all the way out. There is a very strong vacuum at the intake at idle.

Would the iac show a duty load if the cam position was not correct?

Meant to say getting low reading / high vacuum, not low vacuum.

[redlowrey]

The only function of the iac valve is to control the idle speed at the required rpm, if something electrical or mechanical made the engine drop below the required rpm, the duty cycle would increase on the iac valve to bring the rpm back where it should be. I think your exhaust camshaft is one tooth out, and there is too much exhaust gas in the combustion chamber and not enough air to ignite the rich mixture at idle.
That would make the manifold vacuum drop and increase a steady map signal voltage and bring on a 3.2 code.

This is why you have to have the air bypass screw nearly all the way out so there is enough air being burnt in the combustion chamber to idle. If you had the screw out that far the engine would be running at 1200 rpm under normal conditions.

[catacom225]

Sometimes it pays to listen

[Lowery99]

The only function of the iac valve is to control the idle speed at the required rpm, if something electrical or mechanical made the engine drop below the required rpm, the duty cycle would increase on the iac valve to bring the rpm back where it should be. I think your exhaust camshaft is one tooth out, and there is too much exhaust gas in the combustion chamber and not enough air to ignite the rich mixture at idle.
That would make the manifold vacuum drop and increase a steady map signal voltage and bring on a 3.2 code.

This is why you have to have the air bypass screw nearly all the way out so there is enough air being burnt in the combustion chamber to idle. If you had the screw out that far the engine would be running at 1200 rpm under normal conditions.

I get what you keep repeating. I have seen the cams and gears on the second round of rebuild. They were in place when installed and in place after test rotations. The block had to be lifted again and was checked again before it all went together. It is not tough, these engines are very clearly marked for how the timing lines up.

At this point I am ordering a new IAC. With 1 IAC on the engine and disconnected, the other where I can see the plunger, it never moves. Key off, key on, engine on, RPM run up, never moves.... either of them. I can see the duty cycle at 0, 40 or 60, never moves. Also neither of them seat fully at zero duty cycle. Unlikely but after testing the duty cycle, seems to be two bad IAC's (One came with the blown engine, other was used).

However, like I said, if I loosen the IAC bolts a couple of turns and lift the IAC to let air bypass slightly, I can put the idle screw in to a normal place and have perfectly smooth idle at 650 rpm. To me, I would think with a cam out it would never idle smoothly.

[redlowrey]

The reason why I think a tooth out on the exhaust cam you keep getting a 3.2 code meaning a steady map sensor signal voltage, If you had of been able to give a vacuum reading and it was fine, I would have headed in another direction, thinking why is the map voltage staying steady not changing. Why don't you check the operation of the iac valve your self, just apply battery pos and a ground, if it is alright, when you ground it the plunger will retract. You would not think that you would have two faulty iac valves and two faulty map sensors. Your iac valve resistance is in spec.

Have you checked and made sure your closed throttle switch on pin 24 is working, because if the computer does not see zero volts in neutral it will think the throttle is open. If your throttle plate was clean the engine should be able to idle at around 500rpm without any assistance from the iac valve. How have you got your duty cycle meter set up, and what do you mean the neutral switch is triggered.

[redlowrey]

I should of added, the little hole where the map sensor sits is not blocked, I should have asked you that in my first post because if it is restricted that will bring on a 3.2 code.

[Lowery99]

I should of added, the little hole where the map sensor sits is not blocked, I should have asked you that in my first post because if it is restricted that will bring on a 3.2 code.

Yeah holes are all clear, iac and map. By the neutral switch i did mean the little bump sensor for the throttle closed sensor, it is working. Also tested the temp sensor, working as well. We tried 12v on the iac and it just budged, so I think the coils are burnt on my aic, the second is completely bad from what I can see. Used it for testing and now it is 0 ohm and completely shorted - think I did that while not connected to the computer. 12v solid is 100% duty cycle, so it should have gone full open.

Will see when the new one gets here. I'm also not ruling out a bad ecu, if the new iac does not change anything ill order the test connector and pick up the software. Not really a terrible issue right now, it will start and idle, and runs 100% perfect outside of idle, so it is usable for now.

And yeah, I can get it to still stay running even at about 400 rpm as-is, just choppy.