Yes, now the light came on upstairs in my noodle. I don't recall any problems with those , but it should be checked as part of a good checkout.

 

Yes, these are known to go bad and cause the HVAC vent doors to not open properly. It's fed by one of the 4 vacuum lines that come off of the quad connector on the throttle body plate. It is definitely leaking, but I already blocked off that vacuum line and there was no change in the lean condition.

 

I went ahead and bypassed the faulty vacuum reservoir, added in a new check valve and now all the vent actuators are working great. Unfortunately it made zero difference in my lean running issue.

I went ahead and did another "smoke test. This time I removed the rubber intake hose to the air cleaner and MAF and completely blocked off the throttle body inlet. I injected the smoke in to the manifold from the intake connector that would normally go to the PCV valve. I was not able to find any new leaks. However, I was able to maintain a positive pressure in the manifold for 10 minutes after turning off the smoke machine. I definitely don't think I have any leaks in the intake manifold.

If you recall, on the last smoke test, I found a very small leak in the EGR plunger to outside air.
If I sprayed starting fluid at the egr plunger, the STFT would go negative.
I went ahead and replaced the EGR just in case and it made No difference at all.
The only new thing that I noticed at all was that when I run the engine with the air cleaner off, it runs leaner, but I figure this is to be expected.

It just kills me that it is running like it is quite lean, but no leaks can be found.

Anyone have any new ideas?
I'm pretty much at a total loss on this one.

 

Some things to consider,
If there is any way air can get into the throttle body without going thru the MAF sensor , the oxygen sensors pick this up but the PCM is controlling fuel injection based on info it is getting from the MAF sensor.

You might try removing the PCV valve plugging the vacuum leak from it, then shoot a shot of (I like to use carb and choke cleaner) into the engine oil fill hole on the valve cover.
If you get any kind of response in engine RPM it could mean the lower intake gaskets are leaking.

You might confirm there are no exhaust leaks before the oxygen sensors.

 

Hanky,
Thanks for continuing to brainstorm on this.
I did check the rubber intake tube for leaks and did not find any.

There are only two connections into the intake tube prior to the throttle body.
One for the Idle air control valve and one that goes into the drivers side valve cover.

The PCV is on the passenger side and connects to the intake manifold "post throttle body".
The IACV was just replaced and seems to be working well.

I will revisit blocking off the drivers side cranckase vent tube and see if there is any change.

The O2 sensors seem to be reading within spec. and no obvious exhaust leaks can be heard.

On another note, I disconnected the the MAF to see how it would affect things and the open loop setting without the MAF in circuit puts the STFT at +36!
It then idles like crap. The idle is MUCH better with the MAF in circuit and working, but it always idles poorly when cold..

 

If you can, what are the intake air temp and engine coolant temps before starting the engine? When cold ,they should be the same, are they?

When you start the engine cold what are the Oxygen sensors readings, system should be in open loop and the rdgs should be close to 4.5 . are they?

When you say idles poorly, does that mean a rolling idle?

 

Unfortunately, I already started the engine before I got your reply.
The IAT shows in the 70's almost of the time, unless it is a hot day.
The coolant temp starts out around 50 and rises to an expected suitable level a think at about 180 I will have to wait until tomorrow to look at values before first start.

Did you mean volts to sensor for the O2 readings?
Because they show 0.00 before start and almost never go above 1.00 on the real time feed.

When I say idles poorly, I mean, yes rolling. If you put under load even as much as turning on the AC, it improves somewhat.
I can watch the O2 sensor reading bounce up and down from 0.3 to 0.8 as the engine tries to stabilize. You can also hear the IAC valve opening and closing as it tries to respond to the computer to keep things stable.

When the engine is cold, and running at fast idle for the first few minutes, the ST fuel trims are pushed high (as should be expected) and the engine actually runs reasonably smoothly

As soon as one gets off of idle the engine runs smoothly and smoothly on acceleration and cruising. But it's obvious that the engine is running lean, as it hesitates for a fraction of a second on throttle "kick" or when first accelerating from a stop when driving.

This is the last year E250 with 5.4L before they went to "drive by wire". The other unique thing about this year is that is has only three cats instead of four and only three O2 sensors.(two upstream and one down stream.)
It does not look like there is a monitor for the downstream O2 sensor.

BTW, since I had them around and they were cheap, I went ahead and replaced the upstream O2 sensors and it made no difference in readings or operation.

 

I started the engine cold this morning to see if I could find any possible vacuum leaks I had missed by spraying starting fluid around. (everywhere)
Unfortunately, there was no change in idle speed or O2 sensor readings. And I sprayed that stuff everywhere!

I was able to see a change in O2 sensor reading by spraying starting fluid at the outside of the leaking EGR plunger prior, so I know it works..
Nothing in that location now that I replaced the leaking EGR valve.

 

Hey I just wondered what inlet manifold you fitted .. was it the gasket kit or a Dorman type .., could it possibly be leaching across inside the inlet unit ? Is there any drop in coolant level ?
we’ll have to call you Sherlock 🕵️‍♂️ if you figure this one out!!

 

Hey, Briman, Yes, it was the "Dorman type" (now Ford type) with a fitted gasket as part of the manifold.
The coolant level has been steady with no leaks showing. I put pressure on the manifold for 10 minutes after the smoke test and there still pressure in the manifold when I disconnected the line.