Problems at idle

[JHogg419]

Good afternoon everyone. I am sitting here in the hospital after my wife just had a major back surgery and I thought I would get some of your expert opinions. I have a 2004 GMC Envoy 4.2. I bought it two months ago after my wife totaled my car. (which explains the back surgery) After a few weeks it started dieing out while idling. It has continued to have gotten worse. I replaced the spark plugs because it needed them and I scrubbed the TB since I had it off. Throttle body was not that bad. Afterwards, nothing has really changed. I have noticed that when it starts dieing, the alternator drops quickly. Not sure if that is what is causing the car to die or if it is just from the RPMS dropping. It doesn't always completely die either. Most of the time the computer will give it extra gas to save it.

There are no check engine lights or other dash lights coming on. It seems the charging gauge seems to be running at able 13.5 all the time. I figured it should be at least straight up at 14. Once I get my wife better that is what I am planning on checking first. I am just a bit lost. Other than idle, the motor runs perfectly smooth.

Any thoughts???







(Edit: I am sorry if there is poor wording. I have been awake for 36 hours. I am just going stir crazy and I thought a little ORTB would help)

[navigator]

3 items stick out to me...
1. what plugs did you put in it when you replaced it?
2. have your alt and battery tested.

hope your wife has a full recovery, mine is about 1.5yrs out, doing well but will never be the same.

[ErikSS]

I'm sorry to hear about the accident and the surgery. I hope the recovery is quick and complete.

13.5 seems low to me also. I would start with having your alternator, and then your battery tested. Did the truck sit for a long time?

[TBYODA]

Yes god speed on the full recover of your wife.

Did you pull the two pcm fuses 10 & 28 and wait 15 min's so the pcm clear and relearn in start up?

[JHogg419]

Battery went bad about a month ago. Out of no where. No build up or anything just went out and nothing. It was five years old though. I didnt think about it. Haven't tested the alternator yet. It is next on my list. I have just been busy with this surgery lately. In my head, I figured it would still run on the battery even if the alternator wasn't working properly. I do have a SLT with every electrical option possible. One thing I just noticed when I ran out to take a breather. I went to roll up my windows and hit the back two switches not the front too and it bogged down to almost nothing before I let go and it pulled back up. I am thinking alternator....Every vehicle I have owned in my 14 years of driving has been a bit above. I didn't know if all the bells and whistles on my Envoy just kept it a bit lower. I know I don't have to jump it when It sits over night.

Question: What is your charging gauge running at? Straight up at 14? A little under? A little over?

[drburke]

it bogged down to almost nothing before I let go and it pulled back up.

For what it's worth, mine does this too and I believe they all do-- however, not to stall. This immediately raises a red flag for your alternator. Once the vehicle has started, it runs almost exclusively off the alternator. If it almost stalls out because of an electrical overload, it's nearly 100% the alt/battery.

Check the battery connections. Had something similar happen on my 2500. Truck started exhibiting no-start symptoms randomly, then the battery went out (luckily, in the O'reilly's parking lot). After replacement, it still continued to no-start and die at idle from speed. Found out my negative terminal post wasn't screwed in all the way, simple fix.

If that checks out, next step is the alternator.

Your wife is in our prayers here.

[Trail X]

These trucks also tend to sometimes die at idle when transitioning from winter to summer. Something about the fuel differences. The computer tries to optimize the idle, but sometimes goes too far which results in a random rpm crash. But the voltage gauge does sound quite low. I think mines normally a hair above 14.

[Moots1288]

The gauge on my cluster is always under 14 probably around 13.5, never really bother with it cause my scan gauge says 14-14.5 and I have a semi new alternator and my battery is only a couple.months old

[mason9905]

By any chance while you were sitting there at idle was your a/c on?
The reason I ask is I've had a few come into the shop with similar complaints. If so when it starts idling rough shut the a/c off and if it starts idling normal start by cleaning out your condenser and radiator area so it can get air flow if that don't help check your clutch fan. If your a/c system doesn't get proper air flow the high side on your a/c pressure will rise and will start to lock the a/c compressor up temporary which will kill the truck once the pressure drops its fine

[JHogg419]

I think you are right. Last night on my lunch break I left the ac off and it ran perfect for 20 minutes. Turned it on and it started the problems again. How can I check my fan clutch? It doesn't seem loose or anything.

[mason9905]

In most cases itll throw a code do you have a check engine light on? Or the fan will just always be engaged and the fan will roar at higher rpms.

[DirtyBacon04]

swap your AC relay.
it's a common issue we have. still happens to me on occasion.