Unplugged vacuum line- runs better - SOLVED: IAC

[Chapap]

I just replaced injectors and PCV valve. I pulled the top half of the intake manifold to do it. Old injectors truly need to be replaced. Now the truck needs some gas to start and almost dies when going down to idle. It catches itself and gets to a decent idle.

So what makes it better? Pulling a vacuum line makes it quite good. Pulling the vacuum line off the fuel pressure regulator acted just like the non engine related vacuum line. Pulling the PCV “intake” in the valve cover makes it run better. I pulled the brake booster vacuum line and I could get a surprising amount of leakage and the engine would just speed up. Enough leak and it’d die tho. I initially thought I had the wrong PCV valve. The new one has a much weaker spring than the original. It ran a tad better when I put the original back in. Any thoughts?

 

[Dirtman]

Remove the IAC valve. While still plugged in look into the hole, turn the key to the run position and see if the piston moves. If not, your IAC valve is stuck and that's why the extra air from a vacuum leak is allowing it to run better.

 

[Chapap]

Remove the IAC valve. While still plugged in look into the hole, turn the key to the run position and see if the piston moves. If not, your IAC valve is stuck and that's why the extra air from a vacuum leak is allowing it to run better.

that makes sense. I did that but was by myself so I couldn’t watch in real time, buy it didn’t move. It seems to have gotten better today so it’s trying it’s hardest. New valve will be here at the end of the week.

When I’m cruising, the engine really doesn’t like transitioning from power to costing. When I let off the gas, it’s almost a violent transition. Would that be iac?

 

[Chapap]

It’s night and day after the new IAC. Transition from power to coasting is much better too.

 

[cbxer55]

IACs can be troublesome. The El Cheapo $39.95 that Auto Zone sells barely makes it past it's one year warranty, then fails. Went through a bunch of those. Finally, one day, saw that AZ has a "Premium" IAC, made by Hitachi of Japan. Costs double (bit over $70) what the el cheapo part costs, but haven't had to replace it since 2015. Also put one in my Lightning the same year.

 

[Dirtman]

Hitachi is the OEM maker so yes, best to get that if you don't get a Motorcraft. Same with MAF sensors.

 

[cbxer55]

Hitachi is the OEM maker so yes, best to get that if you don't get a Motorcraft. Same with MAF sensors.

That I didn't know. Good to know.

 

[Chapap]

I wish Rock Auto listed country of manufacture in their descriptions. The cheap one didn’t look specifically designed for this vehicle, but made of universal parts for ease of manufacture. I’d describe it, but the pics will do a better job. So I counted that one out and went to the next cheapest that made shipping make sense. It was Standard Motor Products I ended up with... and it had the heart by it.