Good idle cold, low/stumble idle warm or hot

[RichardH]

Hello:

I have a 2001 4.6 2wd XLT with 208k miles.

I have replaced the PCV, and the hose to the rear of the elbow several months ago.

The truck is very drivable. Never a problem with starting cold or hot. I have idle issues when it's warmed up though and in Drive. It seems to hunt a little bit and idles low and surges a little bit. Between 550 to 800 rpm. When in Park or Neutral it returns to stable idle when warm. It has never stalled out but was wondering how to approach this idle issue. I have no CEL lamp on.

So to summarize: low idle only when warmed up and in drive...

Thanks

 

[1997SCEBFEX]

several issues come to mind based on what I've experienced with mine; sure others will chime in:

could be fuel filter
could be Idle Air Control Valve-I'd address this first
could be gummed up Mass Air Flow Sensor
when was your trans serviced last?
when was your fuel and air filters last changed (or re-oiled if you have a K&N or similar)?

 

[RichardH]

Idle control valve was also replaced, should have mentioned that., mass air flow looks clean, air filter changed recently. Two ports to the exhaust sensor were clogged a few months ago, had the elbow removed for cleaning, and CEL cleared up, new sensor too. Pretty clean/clear intake.

I am probable going to do a spark plug and COP refresh. Someone mentioned wires to the COP, or were they referring to the boots?

Looks like I can do the fuel filter and reinspect the ICV for the heck of it. Overall it runs good, but low idle in drive and when warm.

So reevaluate ICV,
change fuel filter
change air filter too
(trans service done recently)
plugs/COP refresh

Thanks for the feedback!

 

[Bwhite]

Sounds more like a vacuum leak somewhere. My PCV hose was cracked where it goes in under the IACV, did the same thing, idled fine cold, looped when warm, did you check the boot that the hose plugs into back there? That was my issue.

 

[grantpa]

I'd second the vacuum issue but also look at leaking (when hot) COP's. I've had a similar issue with my '00 Expy.

 

[RGTFanatic]

I currently have the exact same problem with my '02 5.4 AWD.
I suspect that its one or more of the TCC solenoids. I can feel the TC disengage when I begin rolling from a stop. My RPM's return to normal as soon as it disengages.

FWIW, I have a 4R100 trans w/HD towing package.

 

[RichardH]

Hi, and thanks.

Dummy question but what is the TCC solenoid. I'm thinking some trans issue?

Just looked it up. Trying to figure out what the repair might look like. I read that fuel consumption increases with this symptom and have noticed that too. Not locking up at hwy speeds.

Edit: I also need a neutral safety switch replaced. Don't think this would have any relation to the current issue.

 

[RGTFanatic]

Hi Richard, you're very welcome. Apparently there are three TCC solenoids. One or more of mine were, in fact, faulty. I had my torque convertor replaced as well. One symptom I had was a very low idle stopped at a light/sign while in drive. If I shifted the trans into first gear, while still stopped, the idle would return to normal. I then shifted through the gears manually until I had to stop at the next light. The rough idle was back again. I went through the entire procedure at each light countless time to confirm that it was not an anomaly.

The trans work I had done cured all of my problems. I paid about $500.

 

[RichardH]

OK, again thanks for the feedback all.

Just an update. CEL light just popped on a day ago. Only bank 2 is showing lean P0174 if I recall. So out of the many potential fixes, I'll start to look at some of mayne the lesser expensive options that might help and go from there.

Some other post linked: http://troubleshootmyvehicle.com/ford/4.6L-5.4L/troubleshooting-p0171-and-p0174-page-2

I found some good info there in that link. I wish it was a simple MAF cleaning. I doubt that would only make one bank lean but will do that and a few other options. The computer at AutoZone said that the most likely culprit is the EGR valve. Have not hit that job before. Will need to see some youtube vids to see what is involved.

Most likely it is a combination of a few things: maf cleaning?, small vacuum leak somewhere, maybe a funny injector. I'll also see of I experience different behavior if I change the gears on the 'tree'.

I'll have to do some digging on the weekend if I am not called to the local Ports.

Cheers-
Rich