Surging Idle help - Video attached

[Kegworth]

Just wondering where to begin diagnostics here. I have a vacuum tester and fuel pressure tester, but don't have the fitting for the schrader valve at the moment. Can fuel pressure be tested elsewhere?

Idle was great for quite some time, wasn't an issue until just the other day the gauge stopped working, tank is full however. And now i'm noticing a surge in the idle. Still sits at a good 1.5k ish during warm up, but once it drops it does the surge for a good while before eventually, or not, dying. I did also check for codes and there are none being thrown.

1988 Ranger 2.9L Ranger Surging Video

 

[Kegworth]

Did find this older post and i'll try these tests... any other thoughts appreciated:

"As far as the idle:
With engine warmed up unplug IAC Valve, it should close all the way and idle should drop to about 500, it may stall out so you might have to prop open throttle slightly.
But without IAC Valve connected computer is not controlling idle so if surging stops, it was computer causing the surge.
If surging continues then recheck for vacuum leak with engine at this low idle.
MAF sensor is the start of the "vacuum" area of the engine, it isn't just the intake manifold, any air entering engine without passing thru MAF sensor is a "vacuum leak".

If you have a timing light use that as well to see if spark timing is jumping around causing the surging, use SPOUT connector for this"

 

[Kegworth]

Update:

- I checked the timing and its sitting pretty at 10/12º - kind of hard to tell exactly, but i believe its 12.
- Disconnected IAC valve, idle dropped, but surging seems to still be present. It was stabilizing a bit for whatever reason, so wasn't a clear even surging like it WAS doing. But pretty sure that rules out IAC failure.

 

[Dirtman]

My first thought is you have a vacuum leak somewhere.

 

[Kegworth]

I did a vacuum leak test by using some propane and moving it around various vacuum lines to see if the idle increased at all as a result. I did not find anything, however, I noticed a hissing sound coming from what I think is the brake booster line? Right on the outside of the 90° angle attachment point that looks like Simon says... , so I jiggled it and was able to get it to stop hissing. Could that be a culprit area? I did still proceed to surge and die not long after correcting that.

 

[Kegworth]

Also - i did find this peculiar... what is this hose? It’s very loose and oily, and easily slides out and when removed, i can see faint smoke coming out of the hole.

 

[Dirtman]

Thats the Pcv valve. It is a vacuum source. So is the booster. Both would definitely be an issue.

Unfortunately the propane trick doesn't always work to find vacuum leaks. Besides using a smoke machine the only way is to literally just go over every vacuum source and tighten/test all the lines, hoses, valves, etc. There are also things that can cause vacuum leaks that most people never consider, like your oil fill cap and dipstick...

 

[Kegworth]

I do have a smoke machine actually. Is it as easy as blow it right into the engine bay and see if you can see the smoke get sucked in somewhere? Seems challenging with the fan disrupting the air space so much. Perhaps i can disconnect it temporarily?

 

[Dirtman]

No that's not how you do a smoke test. You stick the hose from the smoke machine into one of the vacuum lines and pump smoke directly into the engine (with it off!)

The smoke will fill the entire intake and all the lines and start pouring out of any leaks. You have to plug the throttle body opening with something though or it will just come out of there.

There are speciality smoke machines for automotive use, not exactly the same as what you would use for a disco party. You can make one fairly simply, or if you like cigars just light a big one and puff away while blowing the smoke into the brake booster hose.

 

[Kegworth]

oooooo nice ok forgive my ignorance... so, somehow downsize the exhaust port like 800% on the smoke machine (haha) and connect it to ANY vacuum line?

Also - check out this video of my PCV valve, lemme know if this is fishy af or if its just me. Doesn't appear to be vacuum either? Seems to push out out rather than pull in, hence the smoke. But not familiar w the routes of the lines...

Ranger PCV valve loose as a goose...

 

[Dirtman]

There is pressure inside the crankcase of the engine from blowby and the crank and pistons spinning around, the PCV valve sucks this pressure out to keep gaskets and seals from blowing and leaking. So one side is pushing, the other sucking. The valve is also metered to flow less at idle and more at high RPM. The valve is connected to the intake manifold (a vacuum source). Replace the valve and grommet. Costs like 4 bucks.