low rough idle on cold starts (3 Viewers)

[Kkxrw]

From all I have read on here, it would point first to (3) things:

Temperature Sensors in the head (You've recently done one)
IAC valve operation.
VSV valve operation.

As I think about what you have done and tested and what changes when the engine comes up to temp:
ECU goes to "Closed Loop" and the fuel pump changes speed. This is determined from the temp sensor.
This also changes the O2 sensor limits the ECU monitors.

Vacuum leaks could be a source, but unlikely.
Does the engine die or get REALLY rough if you remove the oil fill cap while running? It should get REALLY rough and nearly die when you open it. If not, you have massive vacuum leaks the ECU is already adjusting for such as valve cover leaks and/or spark plug tube seal leaks.

Possibly check fuel filters both in tank and under the intake manifold.

Check fuel pressure at idle prior to warm-up and again after warm-up.

Thank you for the reply. I appreciate it.

I will check removing the oil fill cap today. I have not done this yet

I have changed the fuel filter but not the sock in the tank.

 

[logicbyondreaso]

Any more progress on this issue?

 

[Kkxrw]

Any more progress on this issue?

Unfortuantely no. I brought it in to a shop to see if they can help.

 

[Kkxrw]

Just a quick update in case anybody else finds this thread. It turns out my vaf was malfunctioning. Even though it checked out correctly according to the factory service manual it still was not operating properly. I purchased a rebuilt VAF from a seller on eBay that rebuilds them in South Carolina. The truck drives awesome. So happy this problem is solved

 

[Kaosu]

So... after additional usage of my 80 I have determined that the throttle idle up "Choke" knob needs to be held at approximately 1900rpm for the first shot duration of driving or until the engine has warmed up to operating temperature. Once it is up to temp it works well as stated before but for the initial start up I hold my foot slightly on the accelerator pedal and once the car is started the "Choke" knob must be used immediately to lock the RPM and this will negate any coughing, spluttering or stalling.

** PLEASE NOTE**

Firstly the "Choke" knob is more of a accelerator lock as it does not affect an additional flap in the throttle body from what I can tell and it directly pulls and holds tension on the throttle cable.

Secondly I would not call this a solutions so much as I would call it a workaround of the issue until I can come up with a proper solution in whatever form that may take.....

I've attached a photo and video of the location and the way the knob operates in my car.... I have no idea if this is stock or an aftermarket addition though...

 

[ppc]

Correct terminology is "hand-throttle". That is an OEM part that in some markets is installed from the factory. In North America they are installed by the owner after purchase.

 

[Desert Dino]

Just a quick update in case anybody else finds this thread. It turns out my vaf was malfunctioning. Even though it checked out correctly according to the factory service manual it still was not operating properly. I purchased a rebuilt VAF from a seller on eBay that rebuilds them in South Carolina. The truck drives awesome. So happy this problem is solved

Do you have the contact info of the guy from ebay that rebuild VAF? and sold you your new VAF?

 

[Kkxrw]

Do you have the contact info of the guy from ebay that rebuild VAF? and sold you your new VAF?

Resurrectedautoparts in sc