Idling Rough Lately

DenaliHD66

Original poster
Member
Dec 4, 2011
597
My truck has been "gurgling" while idling ever since the weather turned cold. I seafoam at every oil change, spark plugs are brand new, air intake and throttle body have been cleaned, fuel filter is new. What would be my next troubleshooting step? I just printed off the instructions for cleaning the CPAS, so I will try that. Is there a good enough reason to replace the o2 sensors before they throw a code? I have 105,000 miles on my truck with the original o2 sensors/CPAS. I've also seen some threads regarding a secondary air pump and check valve? Not too familiar with either one of those, but could they be contributing to my rough idling?
 

The_Roadie

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Member
Nov 19, 2011
9,957
Portland, OR
Get a scan tool on the O2 sensor data and see if the data wiggles as quickly as expected (1 Hz or greater) before changing it.

SAIS system is almost never involved.

Need a better description of the issue. Is it an RPM variation you can see on the tach? What's the max and min RPM you see on a scan tool? How often does it change from low to high RPM? How many seconds between changes? Is it a change that vasries semi-regularly from low to high, or is it at one RPM for most of the time, and takes a sudden jump to a higher or lower RPM? Was it different in the past? How long ago? What else could have changed?

Or is it a vibration that you can't see on the tach or in a scan tool observing the RPM? If it's 10 Hz, and worse in DRIVE than in PARK, it's motor mounts.
 

DenaliHD66

Original poster
Member
Dec 4, 2011
597
Well the reason I put the CPAS at the forefront was because of the sound it is making. Like a puttering type sound. I'll look into the other suggestions tomorrow and see what I can come up with.
 

DenaliHD66

Original poster
Member
Dec 4, 2011
597
Can't tell exactly whats going on in the video but no, doesn't really seem like the same issue.
 

CaptainXL

Member
Dec 4, 2011
2,445
The 02 and CPAS are known to degrade over time. Bosch's recommendation has always been to replace 02 sensor when plugs are changed. 02 sensor technology pretty much matches spark plug technology timeline for longevity. It was common in the olden days to replace the spark plugs and 02 at just 30,000 miles when they were unheated. So given the conditions many here have been doing just that. Also, it wouldn't be a bad idea to check clean the CPAS but given your mileage I would just replace it with an AC Delco. Odds are that the connector is either leaking or soon will or the screens are clogged or missing (near 99% probability). The CPAS screens are filters and will catch all kinds of crap.
 

Mypetropig

Member
Dec 29, 2011
226
If you recently replaced the plugs, did the trouble start after? If so double check the coil packs and make sure they are seated properly. If they are not seated properly then you will get a misfire. Did you use AC-Delco 41-103's?
 

CaptainXL

Member
Dec 4, 2011
2,445
jeffro312 said:
Hey captain not trying to hijack this thread. But my truck sounds exactly like the one in this video with it almost stalling right when hit gas. Etc. So your saying that's fuel pressure reg.. thanks and sorry for interrupting thread

He was running rich. Are you? Do you smell more exhaust than normal? Or does it smell relatively clean after idling for 5 minutes after a cold start?
 

jeffro312

Member
Oct 4, 2012
442
East Haven,Ct
CaptainXL said:
He was running rich. Are you? Do you smell more exhaust than normal? Or does it smell relatively clean after idling for 5 minutes after a cold start?

Exhaust smells more. Also notice its smokey more but prolly due to the 25-32 degree weather here.. but smell exhaust more then usual
 

CaptainXL

Member
Dec 4, 2011
2,445
jeffro312 said:
Exhaust smells more. Also notice its smokey more but prolly due to the 25-32 degree weather here.. but smell exhaust more then usual

Might need a new one then. Other than a stuck fuel injector there really isn't anything more that could allow excess fuel to leak into the system in open loop.

Stick with the cheaper stuff first and then move into diagnosis of injectors if needed.

But first check your coolant temp sensor with a scan tool. The coolant temp with KOEO on a cold engine should be close to ambient outside temp. The PCM performs a cold start and enriches the fuel if the coolant is cold. If the PCM gets the wrong temp from the sensor then it won't run right on a cold start and may run rich.
 

Old Coot

Member
Jan 2, 2013
58
CaptainXL said:
Other than a stuck fuel injector there really isn't anything more that could allow excess fuel to leak into the system in open loop.

A non-firing cylinder can do this as well ... I would check for a cracked insulator on a spark plug or open plug wire.
 

CaptainXL

Member
Dec 4, 2011
2,445
Old Coot said:
A non-firing cylinder can do this as well ... I would check for a cracked insulator on a spark plug or open plug wire.

That would present itself as a class A misfire and his check engine light would be flashing.
 

Old Coot

Member
Jan 2, 2013
58
CaptainXL said:
That would present itself as a class A misfire and his check engine light would be flashing.

Can you tell it has been thirty some years since I worked on automobiles for a living? It would seem as though I am a little behind the times. No wonder I read this forum so much since the Mrs. & I purchased our Trailblazer eleven days ago. Thanks Captain for your insight. Anything to help get the synapses firing is alway welcome!:thumbsup:
 

DenaliHD66

Original poster
Member
Dec 4, 2011
597
Mypetropig said:
If you recently replaced the plugs, did the trouble start after? If so double check the coil packs and make sure they are seated properly. If they are not seated properly then you will get a misfire. Did you use AC-Delco 41-103's?

Yep used ACD 41-103. The sound is kinda like the sound you get when you are very slowly pouring seafoam into the brake boost line, and when it starts going through the cylinders, the truck bogs down a bit, but in my case, the RPM's seem unaffected, it just seems to shimmy or something. Someone mentioned a misfire-- so I'm guessing it might not always show a "Check Engine Light" in this instance? I'll start with replacing the CPAS as indicated earlier, then replace the o2 sensors and then see where that gets me.
 

cbduffeck

Member
Jan 6, 2013
12
I had the same problem with our TB, It ended up being a dirty throttle body. Make sure it is really clean and the vacuum choke passage way is clear. Also what are the readings from the Mass Air Flo sensor? has this been cleaned?
 

CaptainXL

Member
Dec 4, 2011
2,445
cbduffeck said:
I had the same problem with our TB, It ended up being a dirty throttle body. Make sure it is really clean and the vacuum choke passage way is clear. Also what are the readings from the Mass Air Flo sensor? has this been cleaned?

There is no mass air flow sensor on 02-05's.
 

DenaliHD66

Original poster
Member
Dec 4, 2011
597
Problem solved: Misfire in cylinder 5. Going to replace the coil pack. I absolutely detail the throttle body when I clean it. On the back of the inside of it, there is a crevice in the bottom where grime will build up, and you have to take the edge of a small knife to clean it out. Doesn't make a difference as far as how it'll idle, but I make sure I clean every single part of it.

Going to replace the upstream o2 sensor and CPAS while I'm at it too.
 

DenaliHD66

Original poster
Member
Dec 4, 2011
597
Had my mechanic run a quick diagnostic through OBDII. Was misfiring every few revolutions so not every time. Just motivates me more to get a scanner of my own.
 

DenaliHD66

Original poster
Member
Dec 4, 2011
597
Going to replace ignition coil tomorrow. Cylinder #5 was diagnosed in the diagnostic scanner, so is that the 5th one back if I'm at the front of the truck looking inside the engine bay? Just wanted to confirm it wasn't out of sequence or something.
 

CaptainXL

Member
Dec 4, 2011
2,445
DenaliHD66 said:
Going to replace ignition coil tomorrow. Cylinder #5 was diagnosed in the diagnostic scanner, so is that the 5th one back if I'm at the front of the truck looking inside the engine bay? Just wanted to confirm it wasn't out of sequence or something.

Yes, that is correct. Some of us are pretty self reliant and have faith that we can find the information ourselves. So in that light I recommend a Chiltons manual or maybe Alldatadiy.com. You wouldn't have to wait around here to get simple answers such as this.:smile:
 

gmcman

Member
Dec 12, 2011
4,656
While you have the plug out can you also perform a compression test? Just something to note when you have a misfire like this, generally coil packs just fail and aren't generally intermittent.

Granted a compression test is more valid with readings from all cylinders but just something to check.
 

DenaliHD66

Original poster
Member
Dec 4, 2011
597
Okay well I just replaced the ignition coil with a Delphi, and it is still misfiring. Upon a cold startup, it ran smooth, then when it began to level off, is when it started misfiring again. What now?
 

jeffro312

Member
Oct 4, 2012
442
East Haven,Ct
DenaliHD66 said:
Okay well I just replaced the ignition coil with a Delphi, and it is still misfiring. Upon a cold startup, it ran smooth, then when it began to level off, is when it started misfiring again. What now?

Is it misfiring on same cylinder #5. Switch the spark plug and coil to a different hole like switch 3 and 5 and see of then 3 misfires instead of 5.

This will confirm if spark plug or coil is causing misfire.
 

CaptainXL

Member
Dec 4, 2011
2,445
DenaliHD66 said:
Okay well I just replaced the ignition coil with a Delphi, and it is still misfiring. Upon a cold startup, it ran smooth, then when it began to level off, is when it started misfiring again. What now?

DenaliHD66 said:
I don't have a scanner.

Exactly how do you know #5 is misfiring if you don't have a scan tool to look at codes and misfire counts? Huh??
 

gmcman

Member
Dec 12, 2011
4,656
CaptainXL said:
Exactly how do you know #5 is misfiring if you don't have a scan tool to look at codes and misfire counts? Huh??


Was already diagnosed by another person and was determined it was #5. :duh: :biggrin:
 

CaptainXL

Member
Dec 4, 2011
2,445
gmcman said:
Was already diagnosed by another person and was determined it was #5. :duh: :biggrin:

Well I would like to hear it from him. Unless the codes were cleared last time I'm just not buying it. It would also be more helpful to get a proper scan tool on it and look at live data to see when the misfires are happening. If they are consistent then I would be looking at either yes, a total meltdown of the rings or a burned exhaust valve or more likely a bad connector to the coil or wiring. If it's the rings then squirt some oil in the cyclinder, put the plug back in and take another live data reading.
 

DenaliHD66

Original poster
Member
Dec 4, 2011
597
gmcman said:
Was already diagnosed by another person and was determined it was #5. :duh: :biggrin:

This.


And the rest of these suggestions are beyond me so gonna have to take it back to the mechanics...
 

DenaliHD66

Original poster
Member
Dec 4, 2011
597
Going to get the injectors checked out hopefully sometime this week. Mechanic said there is a good GM cleaner that cleans out all the internals of the engine (much better than seafoam, etc.) and can only be purchased from GM or Ford dealers. If that doesn't solve it, then its on to a compression test.
 

CaptainXL

Member
Dec 4, 2011
2,445
So you don't want to or don't know how to do a compression test?

Basically what i mean is don't send it off to a mechanic to check injectors if you can do a compression test yourself first.
 

DenaliHD66

Original poster
Member
Dec 4, 2011
597
Has been narrowed down to a gunked-up valve. Gonna run a bunch of cleaners thru the throttle body and gas tank and see if that breaks it up. All else checks out fine.
 

gmcman

Member
Dec 12, 2011
4,656
Give this a try, works very well.
 

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DenaliHD66

Original poster
Member
Dec 4, 2011
597
Been pouring lucas upper cylinder lubricant and injector cleaner into the gas tank at every fill up. Also sprayed a full can of Seafoam through the intake. I poured about half in thru the brake boost vacuum line with engine running, then sprayed inside the throttle body with the engine off, let it sit, then fired it up. (it took a few cranks for it to finally start) but so far it seems to already be helping the problem. I'll just keep at it until it stops burning white smoke.
 

CaptainXL

Member
Dec 4, 2011
2,445
What you want for the top end is GM TEC, Chevron Techron Concentrate, BG 44K or MCCC (Mopar Combustion Chamber Cleaner). They all have PEA in them. BG 44K has worked the best for me thusfar. As far as Seafoam goes I don't recommend anyone put anything liquid down your intake or brake booster hose unless you want to bend a rod or squeeze a bearing.
 

DenaliHD66

Original poster
Member
Dec 4, 2011
597
Alright well after running about $100 worth of cleaners through the intake and fuel system, it hasn't improved. I took it down to run the codes, and it was throwing a bunch of codes... I didn't get the specifics, but it also showed a misfire history for every single cylinder. Most were in the 50-100 misfire range, with #6 having 178 misfires, and #5 misfiring repeatedly. Dropping it off next week to get it taken apart to check injectors, valves, and run compression test on it. Words of encouragement?
 

CaptainXL

Member
Dec 4, 2011
2,445
DenaliHD66 said:
Alright well after running about $100 worth of cleaners through the intake and fuel system, it hasn't improved. I took it down to run the codes, and it was throwing a bunch of codes... I didn't get the specifics, but it also showed a misfire history for every single cylinder. Most were in the 50-100 misfire range, with #6 having 178 misfires, and #5 misfiring repeatedly. Dropping it off next week to get it taken apart to check injectors, valves, and run compression test on it. Words of encouragement?

That's a waste of money and your going to get burned. Just do a compression test and fuel pressure test yourself. Also buy a scan tool. Shouldn't be working on an OBDII vehicle without one. Need the codes not just a general explaination.
 

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