Ok so I have a 2004 fx4 with the 5.4. I have 92k miles and just replaced spark plugs and two coils. I also just flushed the radiator fluid. My engine used to idle at 500 Rpms while in drive at a stop. It now recently (after coolant flush) started idling weird. When I come to a stop and sit at a light, it will go down to 300rpms or so and the go back to just under 500rpms. I have no misfires and it drives fine when not at stop in gear. I'm getting 16.3 mpg with mixed driving. It is bone stock and I cannot figure this out. Had the tps checked and it said it was within range. The alternator is not making noise and within range. Is there a coolant temp sensor on these trucks? Because it threw an emissions code that said catalyst below threshold at 195 degrees but I was told by a mechanic that it was air pockets in the cooling system that threw it. I had the code shut off and the light hasn't come back on. I'm so frustrated about this because it is a great truck and has not given me probs until now. Anyone?

 

Forgot to add that my fan clutch is going out but not sure how that would affect idle

 

Anyone? I figured I would get some good responses on this one.

 

I have an '06 with 5.4 .....

The only idle issue I have every had is the past day or 2 but my CEL is also on and I'm throwing a P0351 code (#1 COP issue). I did plugs about 2000-3000 miles ago.

I have been reading here in the V8 forum. I would read there. Several people have reported a variety of idling isshes there and some without throwing codes.

Some of those thread may help.

 

Thanks man... I'll check there. It is so weird man.

 

it wouldnt hurt to clean your mas airflow sensor...

 

I am going to clean mass air flow and throttle body after I replace fan clutch. Someone else said that it could be air in my coolant but I've been driving it for 4 days without any cooling system issues. I've also heard tps sensor... I'm just not wanting to throw a bunch of money at this. I'll try and do the free stuff first. My buddy at gm said that sometimes they have to upload calibrations to the truck's computer to fix idle issues. The ****ty thing is that it is one of those things that is really hard to find.

 

Ok so I am cleaning my throttle body today but the other thing I have noticed is when it is warm and I get to a stop, if I just let off the brake, the truck idles down and doesn't move forward until I use the gas pedal. Almost like it is struggling under load.

 

Clean the throttle body with throttle body cleaner
Clean the maf with maf cleaner
Change the fuel filter

You might want to disconnect the battery while you're doing these so the pcm resets...

Another thing to check is the fuel pump diver module(fpdm).....I've seen a few that have caused crazy idle issues when they're about ready to die from corrosion....

 

And to add to this, it has not thrown any codes for the idle. I had an idle issue a year ago that was similar and it went away for some reason. Could it be alternator dragging the motor? I punched it the other day and the headlights dimmed. Thought that was strange, but my voltage meter on the dash reads where it always has and is plenty above half way. I just had my fuel filter changed about 2months ago, so it can't be that. When I had my plugs and 2coils changed, the battery was never disconnected. I am getting an edge Eco tomorrow. I am getting it for the fuel mileage and diagnostics. Wonder if that will affect it?

 

Correction.... Edge Evolution

 

Go over to the parts store and get the alternator and battery load tested.

 

Ok, got the Edge and put it on. I bumped up the idle by 60rpms and it idles higher but still drops when stopping and surges to save itself. (Goes from 600-490 and back up to 600). I have been crazy busy and haven't been able to clean the throttle body or maf. I will stop by autozone this weekend and get battery and alternator load tested.

I have some questions now:

1) When I roll down the window while the truck is in idle and I hold the button with the window all the way down, the lights dim and my rpms drop until I release the button. It doesn't do this as bad when I actually am using the button to move the window (instead of pushing the roll down button while it is already down). Is this normal?

2) With the edge, will it be pointless to try resetting my pcm but unplugging the battery cable if the edge is on the vehicle?


3) I saw a post where a guy said that air in the coolant can cause this idle issue as well. Like if the air is by the TPS. Possible?

4) People have said the TPS could be the prob, the Throttle Body, The Mass Air Flow, some screw by the Throttle body, my alternator, my battery.... My truck has not thrown a related code to any of these. Will they cause issues without throwing a code?

5) I don't have the money to take it to the dealership and get raped...Is this a fixable problem or should I just deal with it?

 

no money to get it fixed by a mechanic but money foe an Edge? First off, I'd remove the Edge until you have this fixed.

If you believe air in the cooling system is the culprit have you done anything to try getting the air out? Have had the alternator and battery checked? Have you cleaned the MAF or throttle body?

You might try Autozone or the like to see if they have the ability to check you codes.

 

Ok so I threw the p0420 code again. Points to 02 sensor/ catalytic converter. Maybe after changing plugs it threw some carbon. Cleaned throttle body and maf and that is when it threw the code again. It says bank 1 is below threshold. Thinking of taking it to the dealership. They will run the tests my edge can't. Ps, I got the edge for 45 bucks, so that's how I paid for it blue blood