Think about it a minute. Wont run with hose hooked up. AKA a "sealed intake system. If you open the PCV valve hose or end it runs. So needs more air. My first thing I would try is a new PCV valve. Hows the MAP sensor.

 

MAP seems ok. The voltage and the pressure is correct when reading on OBD2 scanner. The PCV rattles when shook but I washed it with mineral spirits and it didn't change anything.

 

Do you have vacuum in the hose when it is disconnected? Where exactly does the hose go from/to?

 

The hose goes from the drivers side valve cover to the back of the intake near the EGR valve. Yes there is plenty of suction when it’s disconnected that’s how I realized I accidentally left it off. I can get a suction reading while it’s disconnected if it would help anything

 

How about the Idle Air Controller? I've seen those plungers either plug off or fail entirely causing the same symptom.

 

The IAC is built onto the throttle body but I pull the throttle body and check it. I believe it’s nonserviceable but I will check it for anything obvious

 

I am a teaching assistant in an auto tech class for high school students and I just discussed this with the instructor. He feels that you have a throttle problem. What seems to be happening is that when you disconnect the hose it allows the engine to get air through the hose, then when you hook it up the air flow is restricted killing the engine. Hope I explained it so you can understand it. If not let me know. I don't know if there is an idle air adjustment on this engine or not.

See above post.

 

IAC makes a point. It does exactly that , what AF26yr says. I am also an assistant instructor in automotive tech class. The IAC lets more air when you put a demand on say the power steering at idle or the AC kicks on. It allows air to basically by pass the throttle plate and up the idle.

 

I pulled the throttle body and cleaned it up. It wasn't terribly dirty and I popped the IAC controller cover off and didn't see anything really obvious. The throttle plate moves easily and the gears on the IAC didn't look worn. Is there anything I should've looked at closer? I did clean off some of the copper contacts in the IAC motor. I used an eraser and compressed air to remove the eraser shavings. It didn't change anything as far as idle goes. Oh yeah and I did make sure to put a new gasket on the throttle body when I reinstalled it.

 

So does it run rite now? Is it fly by wire or have a cable from gas pedal? How many wires go to the plug @ throttle body? I tried to find a wire diagram and so far no dice. So kind of throwing stuff to see what sticks here but here is what I would try. Pull plug on MAP sensor and see if will run, if no go hook back up. Pull plug on TB and try it. With a DVOM key on see if you get voltage at wires @ TB. I would think at least one would be power. How was the port the IAC is supposed to get air thru? I would maybe try a jumper and see if I could get the IAC to drive and it run rite.

 

No it still does not run correctly. It is drive by wire. There are 6 wires in the plug for the throttle body. I will go and pull the plug for MAP sensor and I will check the TB for voltages with key on and off and running.

 

Interestingly, the next post that came up as Recommended Reading was a V-10 post and it turned out to be an intake gasket that did not show up when fluid was sprayed around it. It was discovered by watching the O-2 sensor reading as it warmed up. Just a thought.....

Kevin

 

I pulled the MAP sensor plug off and started it up and it idled great even better than before. The plug going into the throttle body I had 4.7-5 v DC on 2 wires. I'm assuming a signal wire and return wire but without a wire diagram it's hard to say exactly. The ETC light did flash on and off while idling without the MAP sensor plugged in. I did check O2 sensor voltage readings and they were between 0.5-0.85V the whole time while running and I idled the truck to operating temp. Does that mean my MAP sensor is bad?

 

Hmmm so talking with boss today, With map disconnect it should go rich. Which is oposite of an open air line like egr. So whats the air filter look like? If it idles with map off, while its running reconnect and see if dies.

 

Air filter is brand new and I had the PCV hose attached the whole time it was idling.

 

OK had a round table discussion with boss today. Well across the office at lunch anyways. But tossed this back and forth. With the MAP/MAS disconnected it should go rich and closed loop. Which if already rich, which is what the open hose runs OK synario indicates it should choke out. But boss man had this interesting thought. What if the MAS sensor has failed and causing the PCM to go way more rich than open loop rich. Then when disconnected the PCM goes to "normal" open loop rich and can run. I dunno I'm outa ideas rite now. Whats a MAP sensor run?

 

Ok I was checking things out and while the MAP sensor is unplugged it did go rich and closed loop. I verified with the scanner. Now it was idling high enough to stay running by running rich, so what would cause it to go so lean that it won't idle with the PCV valve attached?

 

MAP sensor at advanced auto is just under $20 out the door. I ordered it and will pick it up and install and let you know how it goes. What is MAS? Mass air flow?

 

Usually have one or other I think. MAS=mass air flow MAP=manafold absolute pressure.

 

The only codes it has been throwing is P0300 random cylinder misfire

Missfires can stall an engine. You need to fiind out why it's throwing the code. When where the plugs replaced last? If the plugs aren't firing of course it wont run correctly. And a failing iac can cause the motor to stall because it's not adjusting the air fast enough to keep it running.

 

The plugs and coil packs and wires were replaced less than 50 miles ago. This is the 4.7 with 16 spark plugs the upper bank has the coil pack on it and the short wire down to the lower bank plugs. I made sure the gap was correctly set on the plugs when installing them

 

If its fly by wire throttle body, more than likely no IAC as the computerized, electronic controlled throttle makes up the idle speed compensation.

 

With the PVC open it is letting more air (not metered) in to mix with extra fuel. So it is leaning back. If you have another vehicle pull the PVC and see how it runs. But the open pvc is an indication of rich if it smooths out.

 

does anyone here see anything that stands out that my be able to help figure out why it will idle fine with PCV hose off but when driving whenever you start to slow down it will die but if you keep foot on gas and RPM up it will stay running. This was on a cold start and immediately the CEL came on for P0300

 

You need to either cap or hook the egr valve back up! Do not run it with it open, It is sucking in air there and the iac can not adjust the idle accordingly. Did you sort out the problems with the misfires. You need to get it running on all cylinders before you do anything else. Completey disconecting the map sensor the pcm will now have to run off of a default setting(no input from the sensor) so it can keep the engine running. Don't disconnect things just to see what happens.

 

I have everything hooked up but still with the pcv hose attached the truck won’t idle. I’m still getting p0300 as soon as I crank the truck. It never narrows down to 1 specific cylinder. The MAP sensor I replaced and it is hooked up. I’m wondering could it be a bad o2 sensor that is making it shut down? If the o2 sensor is leaning out the motor due to a bad signal it could cause these issues couldn’t it?