My last hope on my rough idle

[Nick from NE]

Hello everyone, as the title states this forum is my last resort before I fork over the cash to a real mechanic.

(video link at the bottom if you care to see it)

First, the issue - the vehicle has a rough idle that gets worse as the weather cools, (the engine temp doesn't affect it) at its worst it shakes the cab and has even stalled out at a light (once in 20,000 miles) in high temps it runs almost normally.


Some info on the vehicle and some of what I’ve done so far.


2000 ford expedition Eddie Bauer 5.4 triton 2 valve awd - 4wd


Codes 171 174 and P0300 the random misfire is only if I let it idle for a while, the lean codes are always there if I’ve driven a bit or idled a while

189,000 miles

fairly small hole in muffler

Engine rebuild at roughly 110,000 miles i’ve seen the receipts and I don’t think the last guy was smart enough to fake them…. Not entirely sure what was done in this rebuild though so take it with about a pound of salt.

Fuel pump at 111,000 according to the grease pencil under the hood

New MAF

Smoke tested for vacuum leaks found some (PCV elbow) , fixed slight improvement

Cleaned original AIC valve with no affect then replaced it with a motor craft one - small improvement in idle.

New battery, not sure if this could have an effect but still

New fuel filter

liquid moly engine oil flush

Injector cleaners of all sorts

Spark plugs

Ignition coils

Replaced faulty upstream passenger side o2 sensor

Regular 3000 miles oil changes with various high end 5w 30 synthetics for the last 20,000 miles Passenger side exhaust manifold gasket

IAT sensor

Air filter

Pulled and cleaned sediment from fuel tank, (learned that a light bulb is an effective redneck fuel float.

AAT sensor

New Napa metal PCV valve

Removed and cleaned entire throttle body.

A few new vacuum lines that were cracked.


Since doing all this I’ve done multiple smoke, water and propane tests looking for vacuum leaks but I’ve found nothing.

I'm attaching a two minute video showing the tac and some live data, as far as I can tell its only really bad in open loop, in closed it appears to be able to compensate, under load the trims improve some but at best it is still adding about 7% on both banks. it only seems to switch to CL if I rev it a few times.

Note on the video - I rev it at the beginning and then I don't touch the gas, brake, ac or anything else for the remainder of the video.

Link to the aforementioned video on YouTube because the quality drops when I post it here.

https://www.youtube.com/watch?v=zG9NPIIJcw0

I really appreciate any help, thank you.

 

[Billme]

I’m going to say you need a new computer..When you have done all that, with slight changes, you need to consider it..I just went through something similar..

 

[Nick from NE]

I’m going to say you need a new computer..When you have done all that, with slight changes, you need to consider it..I just went through something similar..

That's ominous, how would I confirm it?

 

[DieselMonk]

Check the actual fuel pressure. A plugged CAT can throw lean codes, stalling, misfire…

 

[Nick from NE]

Check the actual fuel pressure. A plugged CAT can throw lean codes, stalling, misfire…

Good call on the CATs I'll take a look tomorrow, fuel pressure came to 35 at idle and 35 at 2000rpm in park, it seems to me it should have jumped when I hit the gas but I've read mixed things so I'm not sure.

 

[DieselMonk]

Did you look at the fuel pressure while the engine acts up?
Go around the fuel injectors and see if one is loose. There is a video about it, sucking unmetered air into one cylinder. They should be tight, no little wiggles.

 

[DieselMonk]

other than that, I am thinking the intake gasket is leaking. Take a bottle of water while engine running and give it a good squirt of water. If there is a leak the engine starts to shake and miss. The leak may be so tiny that you may not see it with the smoke unless you know where it exactly is. After that, I am out of ideas for now.

 

[eurolux]

My 5.4 was running/idling rough but no error codes. Someone suggested a smoke test and I found several vacuum leaks, especially around the PCV, and I fixed all of them. It ran a little better but I wasn't happy. It turns out it was the rubber attachment from the PCV hose assembly on the back of the Idle Air Control Valve. The smoke test didn't show any evidence of a leak back there but I put my hand behind the valve and sure enough there was a small hole. When I replaced it (I have attached a photo with what I ordered from Amazon) the entire rubber piece practically crumbled in my hand. Not sure if this will help in any way but it made a world of difference in how my 5.4 idled/ran. Good Luck!

 

[02Sexpedition]

Have you changed the coil packs and plugs?

 

[jr1under]

This is just speculation but what would cause multiple cylinder misfires if the plugs, coils and injectors are all good? Could it happen from damage to the wiring harness between the cylinder banks and the PCM?