Mystery for the TW Gods

Well, after five years of ownership, and six years of reading this forum, I FINALLY had to sign up to ask a question I couldn't find an answer for. So here it is, my VERY FIRST POST. First off, thanks to this forum, and this one alone, I can say I have been able to troubleshoot and fix every problem (which is almost none) I have had with my truck. The information found here is absolutely unreal, and is an amazing resource. I used to read the paper in the evening, now I just read this. My truck is a 2007 access cab V6 4x4 auto and it has been an absolute dream to own. It still is actually, but I have finally found something that is really starting to bother me that I can't figure out, so here it goes...

I've got just over 178,000 miles (285,000 kilometres) on my truck and as the temperature starts to get colder here in the north, I've noticed the truck starting to idle a little low but only in one set of circumstances: Cold weather, in drive, stopped at a light, with the heater fan on high. Turn the fan off, idle smoothes right out. Battery is new, intake air temp sensor clean, spark plugs are new, etc. This truck is always maintained, everything is up to date. Now, it will do this in the summer as well with the A/C on high, but it is more noticeable in winter when the outside temperature is lower. It doesn't idle irregularly, just a few rpm lower, just enough to feel it in the cab. Also, it doesn't matter if the A/C compressor is on or off, the factor is the fan on high. I have searched, and read as many related threads as possible, so I will apologize ahead of time is someone can easily knock this one out of the park.

 

Have you ever cleaned the throttle body or MAF sensor? Both should only take about an hour.

 

If you have it on recirc the A/C Compressor runs. It is possible that could be an issue along with a dirty throttle body.

 

Normal, don't worry about it

 

Both, no change.

 

Awesome, welcome aboard! Mine seems to do the same at idle and I notice if I put in neutral it's back to normal. My truck is a 2015 with the 4.0 V6.

How is your 07 holding up as far as rust is concerned?

 

Turn on some other electrical devices with fan on high - such as wipers on high and high beams. If rpms drop further, I would suspect the charging system, either faulty connections and/or deteriorating alternator. Connect a voltmeter and read voltage when you turn on the electrical devices to see how much the voltage drops. Output at idle should be 13.5+ volts. Voltage drop with electrical devices on should be about half a volt.
https://www.familyhandyman.com/automotive/how-to-test-an-alternator/view-all/

 

It's doing really well actually. I have a few surface rust spots, but nothing major, yet. It was garage stored and not winter driven for the first five years of its life, so that might have something to do with it. I did have it inspected during the recall and sprayed, but not sure how well their product really works. The techs at my local stealership aren't exactly artists with the stuff.

 

Excellent, thank you. I will try this. Any idea how long the alternators last?

 

150K plus or minus 50K. This is a rough estimate as there many variables in play.

Here is another good source of alternator info that correctly points out you can have a bad alternator without the dashboard battery/charging light turning on.

http://www.econofix.com/alt.html

Do you have some of the other issues? Like headlights dimming?

 

No, that's the odd part, no other issues. I can turn everything electrical on: high beams, fog lamps, the plug in the box, everything. I can even turn the truck off with everything on and it turns over without hesitation. RPM never drops, nothing changes, the truck is a dream. But as soon as it's a little cold out, and the fan is on high, I lose just enough RPMs at a light to feel it, just barely.

 

I don't have an answer for you question, but welcome to the site!

 

Check the blower motor motor resistor connector. When the fans start to go bad the cause the plug to melt. You may have a short there.

 

Btw, welcome. Also, judging by your statement above, you have clearly mastered the "search" function. You have meritoriously been promoted to search feature use instructor and are now in charge of all noobs. GL.

 

are you blowing air onto the windshield? If so, that mode runs the A/C compressor and that is what is causing your rev change. It's completely normal. If you don't like that, there is a mod that changes the behaviour (I've done it) that works great

 

I agree with the above posts.. checking the blower motor smd resistor connectors is good idea. Realistically the idle is going to change, it's going to hunt around a little. The a.c. clutch will kick on when the dash vents are set to defrost under normal operation

 

Not running the A/C when this problem occurs. I'm familiar with how the compressor cycles and that system is working correctly, this is something different.

This is new information for me, excellent! I'll check it out shortly... LOL I spent days searching for this info... had I just known the proper terms I might have actually found it! Either way, here we are and once again TW comes through.