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Idles rough after warm, some surging with light throttle while driving?

markwoodlief

Full Member
Joined
Feb 7, 2015
Messages
63
Location
Mount Vernon, WA
As the title states my truck seems to idle rough after it gets up to operating temperature.

So far I've done:

  • Changed Plugs
  • New MSD Wires
  • Cleaned MAF with MAF cleaner
  • Cleaned Throttle body with throttle body cleaner, then a seafoam session
  • Seafoam in the tank
  • replaced both EVAP valves, 1 under the hood near the throttle body, the other under the rear of the truck near the spare/exhaust/gas tank
  • Replaced Both Upstream (before cat) 02 Sensors


I had a check engine light a few days ago, P0455.  Which led me to replacing the two EVAP valves, light is off after that.  Not sure which one I needed so replaced both.  Cheap and easy to do.

I'm thinking I'll need to bite the bullet here and take it into a service center.  I'm a fairly good wrench at home, but thinking a service center will have the more advanced diagnostic tools that I don't have.  I've checked codes and there are none now.

I also should mention I can hook my truck to my laptop and get real time logging data for anything available in the OBDII for the Avalanche, which is quite a bit actually, but... I have no idea what i'm looking at.

I looked at the volts for the O2 sensors, trim levels, etc.  But not sure what the volts are supposed to be for each piece.  So am not rulling out a funky 02 sensor or even a cat at this point.

This is a 05 with 113k on it.  Any thoughts on this?  My wallet would much appreciate it.  :help:
 
When warmed up the front O2 sensors should be bouncing up and down.  Short term fuel trims dither the fueling around stoich AFR.  The narrow band sensors are above 0.45 volts when rich, below when lean.  The PCM goes to a fueling level wear small amounts of dithering result in sensor readings on each side of 0.45 volts.

Where are your long term fuel trims at idle?
 
enoniam said:
When warmed up the front O2 sensors should be bouncing up and down.  Short term fuel trims dither the fueling around stoich AFR.  The narrow band sensors are above 0.45 volts when rich, below when lean.  The PCM goes to a fueling level wear small amounts of dithering result in sensor readings on each side of 0.45 volts.

Where are your long term fuel trims at idle?

give me about an hour and I'll report back what they are.  Currently getting kids up, fed, and off to school, then I can go out in the shop and 'play'  :cool:
 
Ive been having issues posting images, let me know if you can see this.  The image is large so may need to scroll to the right to see the Long Term Fuel Trim.  I cut out most of the data and left what I thought may be relevant in.

idledata.png
 
Check your air filter, has your fuel filter been changed?

Also you should check your fuel pressure. A fuel pressure gauge is a cheap investment.

What are you using to scan your truck? Just curious since I have a couple different software packages on mine and thinking about getting the HP Tuner package.

Rodney
 
redheadedrod said:
Check your air filter, has your fuel filter been changed?

Also you should check your fuel pressure. A fuel pressure gauge is a cheap investment.

What are you using to scan your truck? Just curious since I have a couple different software packages on mine and thinking about getting the HP Tuner package.

Rodney

Air filter is newish... Haven't checked my fuel pressure yet, and I have no idea if the fuel pump/filter has been changed out in the past, I got this truck used with 100k on it already.  I don't have the classic symptom of hard starting, so haven't started pulling the tank or cutting the hole yet.

I use this for diagnosing and logging


http://www.scantool.net/software/scanxl-pro.html

, but don't have a tuner for this truck yet.  I had the predator for my H2 which worked pretty good, thinking of getting the Diablosport Intune next.
 
The O2 sensor voltages look good, but they still may be switching slowly.  With those miles and that age of truck I'd try replacing the two forward sensors.
 
enoniam said:
The O2 sensor voltages look good, but they still may be switching slowly.  With those miles and that age of truck I'd try replacing the two forward sensors.

Forward = Before Cats = Upstream?

I was thinking of doing those today just for the halibut.  Cheap and since my truck is lifted, super easy to get to.
 
enoniam said:
Yes, the ones between the engine and the cats.

Thanks.. off to shower, coffee, autoparts store, garage to go have fun with the truck, :)

I'll keep you posted if that turns out to be the issue.. If you are anywhere close to western wa, IOU a sixer.  (y)
 
2 new Denso 02 sensors in.  Same issue.  I went and drove it about 30 miles afterwards as well.  I may disconnect the battery for a bit to see if the computer needs to relearn with the new sensors in or something.

Kind of at a loss.  One thing I noticed about my data logging is that once the temp reads 195, it stop recording the temperature, seemed kind of odd to me.

coolanttemp.png
 
I am far from an expert but I also notice when it reached temp the truck went to removing fuel at -7 then went back to -2. I think maybe the fan kicks on at that point also but not sure that would cause or should cause the fuel adjustment. Just pointing that out Is the engine in closed loop or open? Probably closed but this might also be an indicator but I really don't know.

Just for an example my Fiero is a little rough until the fan kicks on.
 
Same here LornesAV I use Scan XL pro also I have never seen the reading drop off like that.

Maybe the charging system is bad. How does the volts gauge look like, does it stay at 14 volts.
 
ronthehandymanga said:
Change the EGR valve.  (y)

How confident are you?  Initial search doesn't yield much for an EGR Valve for my 05, looks like the 02's had some issues.  Note I did replace the vent valve and purge valve already.
 
MS03 2500 said:
Same here LornesAV I use Scan XL pro also I have never seen the reading drop off like that.

Maybe the charging system is bad. How does the volts gauge look like, does it stay at 14 volts.

Battery looks brand new, as does the alternator.  But I didn't change them, assume the previous owner did.  Charging system seems just fine, holding at 14v'ish when running.
 
Is the coolant gauge in the cluster holding around 195 when the scanner quits recording?
 
enoniam said:
Is the coolant gauge in the cluster holding around 195 when the scanner quits recording?

it gets up to like 220-230 and holds... I may have turned off that PID during that data logging session mid way through, going to do another data log this afternoon, since I've re cleaned my TB, including the backside. (not sure who the braniac is at Gm that ran the hoses into the bottom of the throttle body from PS to Radiator), as well as put 2 new 02 sensors in yesterday.
 
We had a 95 pontiac transport with the 3.8 in it and when going down the highway at cruise speed it would jerk like it had a miss. We changed the plugs and wires then the coils and it was still there, then I took it to the stealer and they put plug and wires in to it after I said I had done it and demanded the plugs and wire they took out.  then I took the rep for a ride and made the van do it for them and it came down to changing the EGR valve to solve that problem, so I just put that out there for you to consider in your quest for a fix.    (y)  R.
 
ronthehandymanga said:
We had a 95 pontiac transport with the 3.8 in it and when going down the highway at cruise speed it would jerk like it had a miss. We changed the plugs and wires then the coils and it was still there, then I took it to the stealer and they put plug and wires in to it after I said I had done it and demanded the plugs and wire they took out.  then I took the rep for a ride and made the van do it for them and it came down to changing the EGR valve to solve that problem, so I just put that out there for you to consider in your quest for a fix.    (y)   R.

Appreciate it.  It seems on the 02 Avy the EGR valve is right there in front of your face.  On my 05 it's still a mystery as to where it is actually located.  I search online for a while this AM, to no avail.
 
220-230 is a bit high.
 
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