08 Ford Fusion Idle Rough (rat nest in air cleaner!)

[wolfehunter]

Did try the idle relearn a few times early on in this process but the car would usually stall a few times before coming up to temperature and completing the full process. And I remember turning the AC on per the relearn instructions and noticed that the rough idle went away while the AC was on. I did drive the car to work one day after that relearn attempt which was 20 miles round trip and check engine light came back on with no change to idle.

The idle air control unit is located right on the throttle body and I checked the resistance on it. It is 4.8 ohms. There are no screws or bolts holding on the black plastic looking cover that is over the IAC. Is there anything in there to clean? I see you can buy IAC gaskets for the unit but there is no actual valve to replace. Looking at all angles but surely missing something.

 

[clinebarger]

Originally Posted by gathermewool
Fuel trim is irrelevant until you drive the car some. They're not called long-term fuel trims for nothing'.

There's a Short-Term Fuel Trim value that reacts VERY quickly after closed loop.

 

[gathermewool]

Originally Posted by clinebarger
Originally Posted by gathermewool
Fuel trim is irrelevant until you drive the car some. They're not called long-term fuel trims for nothing'.

There's a Short-Term Fuel Trim value that reacts VERY quickly after closed loop.


IME, STFT fluctuates too wildly to be useful. LTFT is the long-term average of STFT.

The best way to determine actual fueling is to log both. The sum of both will be actual fueling. One cell, say in an excel spreadsheet, may not give you the full picture, it hundreds of cells will. I'm not familiar of ways to log outside of my own Cobb Accesspprr, which costs hundreds of dollars and doesn't support the OPs car.

I use the DashCmd app and a cheap OBD dongle for all other cars that I use offers instantaneous fuel trim, but I haven't figured out how to log (no real need to).

The lower right gauge is LTFT.

 

[clinebarger]

That hasn't been my experience, STFT's are very useful, Especially after a reset of the trims before enough long term data has been stored to learn LTFT's.

If you have a big enough vacuum leak to cause idling issues.....Both LTFT's & STFT's will be maxed out (Positive). STFT's respond so much faster to fueling changes which makes them invaluable in finding/proving vacuum leaks with alternative fuel sources such as Propane, Carb Cleaner, & Brake Clean. Propane is my favorite but not everyone has the Whip & Adaptor to use it.

Here's a short log of the cammed 6.2L in my Camaro, Drops into closed loop at the 2m 48sec mark, As you can see....The STFT's are pretty stable, Though it is making some corrections for being a little rich, Which is the way I tuned it.

 

[zzyzzx]

Originally Posted by wolfehunter
Sure enough there was a large rat nest built in the air cleaner with bird feathers, corn husks and the like.


Did you take any pictures of this?

 

[gathermewool]

I take back what I said. STFT is useful if there's an obvious issue, since you'll notice an obvious trend toward high pos or neg numbers.

I guess I'm biased by only having had minor issues discovered due to monitoring fuel trim. Eg, I had a torn turbo intake that made some squealing noise that only produces pos 8% or so LTFT that wasn't obvious by monitoring STFT only. By the time I noticed the high fuel trims, LTFT cells were already populated

 

[wolfehunter]

Sorry, no pictures. But it was about the size of a cantaloupe. As a last ditch effort before taking to a garage I ordered a new throttle body and will report results.

 

[wolfehunter]

Replaced lower intake manifold gaskets and also the new throttle body did not fix it. Took to local garage and his code reader suggested cylinder #3 misfire. He cleared code and swapped coils and plugs with cylinder #6. Started car and threw code pointing to cylinder #3 misfire which ruled out the coil and plug being the problem. He said it is pointing to the ECM/PCM (computer) and to take to Ford dealer as they would have better means of diagnosing. I know they will charge me a lot just to hook up to their diagnostics so I've come this far and am not willing to give in and take to dealer! Did some research and the original coils were known to cause the coil drivers in the computer to go bad. Exchanged some emails with a company from Illinois that repairs these computers. They asked that I replace the coils and spark plugs and see if it resolves the problem. Although they do feel from the things I described to them that the coil driver needs repaired. They ensured me that the computer doesn't and won't ruin the new coils but that the original coils would damage the computer. I got the new Motorcraft coils and am waiting for the spark plugs to arrive from Rockauto. We'll see..........

 

[clinebarger]

This is ridiculous!!! I would bet money it's NOT the PCM! The ignition coil primary control transistors in the PCM are VERY hardy.
Unless you have a P0352......I wouldn't even think PCM. Even if you did have a P0352.....It more likely a wiring/connection issue than a PCM Driver/Base Transistor issue.

Don't forget about an Injector causing a misfire & setting Bank 1 lean DTC's.

I've only replaced a handful of Ford & GM OBD2 PCM's not counting the one's I bricked from "Adventures in Tuning".

There has to be a good Diagnostic Tech in your area, I don't see how it's cheaper for you to blindly throw parts at it!!

 

[wolfehunter]

Ordered a set of fuel injectors since I will have everything apart and will replace them the same time I replace coils and spark plugs. Good maintenance as she is planning to keep the car a few more years. It has been a problem free vehicle to this point so not complaining at all about it. If the new plugs, injecectors and coils don't sove it I am left with the option of sending the PCM for diagnosis to see if coil driver is fried. Check back for more scoop soon!

 

[mk378]

And load up the parts cannon for another round.

Have you established does it fire good on all 6 when driving, or is the cylinder cold dead? Problems only at idle are a different diagnostic track. If you were that interested in doing diagnosis.

You could check the coil driver by hooking up the coil outside the head to a test plug and watch if it makes good sparks.

 

[wolfehunter]

New coils and ijectors did not correct the problem as predicted. For kicks I took it to Autozone to hook up to their diagnostic reader. It threw the lean condition in both banks and points to replacing the canister purge solenoid. I did some research on these and they can actually cause a lean condition, poor fuel mileage and rough idle if the valve is stuck in the OPEN position. In my mind I would think it would throw a different code like in the p0400 range but I have tried everything else besides taking it to a dealer.

Going to pull it tonight and see if I can test it by powering it on and off and seeing if I can blow air through it to determine if the valve is operating as it should. I still did not give up but this is wearing me down for sure!

 

[wolfehunter]

Upon locating the Canister Purge Valve unit on the inner passenger side fender well behind the engine and along the firewall I attempted to remove it tonight after work. I had to take the air intake manifold off and squeeze my hand back there to try and unhook the two hard plastic lines that come off the unit. The top one was the easiest one to get at and I noticed that both lines ran up to the top of the firewall and over towards the driver's side. The top one then came off the firewall and ran into the intake manifold. AS my hand squeezed back there to try and pinch the clip holding the line on I felt something jagged scratch my wrist. There was a crack/hole in the plastic line. I found the vacuum leak that was making the computer sense a lean condition and dump fuel causing the rough idle and poor gas mileage. Ford stopped making this line so I cut it at the leak and used a rubber piece of fuel line with two stainless steel clamps to splice it. Hooked it back up and it runs terrific!! Thanks to all for their help.......I was close to throwing in the towel.