Rough idle and misfiring, but no codes

[Blckshdw]

About 5 minutes into my morning commute, my TB started to idle funny. Accelerating from the stop light was responsive, but shaky until about 30mph, CEL began to flash around 40mph. Next stop light, checked the Scangauge... No codes CEL would only flash when traveling above 40mph, which I thought was strange, and after 10 more minutes driving to work, STILL no codes.

I've got about 73K miles, had my spark plugs replaced once since I bought it. I had noticed for the past couple of months, it would idle high (between 750 and 900) when cold, first thing in the morning before I got onto the main road. 2 weeks ago, I pulled coil packs 3 and 4 to get better access to the lower bolts to remove and clean my throttle body (I misplaced my universal joint ) Would it be possible that one/both of them became unseated because I didn't torque down the bolt enough and it started to back out?

I plan to check the coil packs, and wire connections when I get home, but if there are still no codes, what other items should I take a look at?

 

[Blckshdw]

Small update, went outside during lunch and let it idle for a bit, after sitting there for a couple minutes, a steady CEL came on, and threw a P0305. So at least I've got a better troubleshooting point after work.

 

[RayVoy]

Hey Carlton, sup

I think your on the right rack, a flashing CEL is always a mis-fire.

May be a bad plug, may be a water problem, but probably a bad coil.

 

[Blckshdw]

Picked up a coil on the way home and got it changed out. Seems fine in the parking lot, will probably take it for a spin around the block after dinner just for peace of mind. All I know is, DAMN these things are expensive, and I didn't even get a Delphi one (couldn't find them, or I would have)!!

 

[drwfaulk]

which coil pack was it? i had a problem with #4 cause the hood seal was leaking right on top of it, might want to check that out(just my)

 

[Blckshdw]

It was #5, I'm guessing it just lived it's life. We haven't had any rain in a while, although that's probably going to change next month I did get another reminder, I need to do some engine bay detailing though....

 

[Voymom]

We had the same shaky idle when we were getting the p1345 and p0014 the shaky idle was gone when we cleaned the CPAS, just a suggestion from experience as it could be a number of things when there is a shaky idle.

 

[Blckshdw]

I'll keep that in mind. Just went for a short drive around the block, back to rough idling, and flashing CEL, but no code yet. Damn my TB is slow to figure out what's wrong!! If it tells me the same cylinder is having the issue, then I guess I'll have to look at the plug next.

 

[gmcman]

had my spark plugs replaced once since I bought it.

Do you know what plugs went back in? Who did the plugs? Reason I ask is these coil packs pretty much go forever and the only issues that have been consistent are with good ole #4 getting wet. If you lost #5 then I would be concerned what plugs are in there.

 

[Blckshdw]

I'm not 100% sure what plugs are in there. Carmax replaced them as part of their 60K mile service (requirement per the extended warranty terms) The guy tried to cut me a break on the price, so the spark plugs aren't listed on my receipt, but on my previous service write up where they suggested the service, it says 41103 Spark Plug, which is the magic number. I do remember complaining to the guys at a meet shortly after this, that my mileage had gone down a lil bit. It was still within the normal ranges, but since I had just bought my Scangauge a month before, I was always watching my average MPGs and it went from really good to average, but couldn't figure out why.

At any rate, gonna walk over to AA when they open in a lil bit, and pick up a spark plug socket, and maybe a spare spark plug and some anti-seize for good measure. Probably won't get to take things apart until later in the day though.

 

[The_Roadie]

P0305

which coil pack was it?

Everybody should memorize this code: P030X is a misfire in cylinder "X" and they're numbered from front to back (on the I6).

 

[Blckshdw]

It gets better. Looks like the 2nd drive cycle is when it throws it's codes. Let it idle for a minute, and it kicked back a P0300, random misfire. After saying a few choice words, I took a walk and picked up 6 new plugs and the socket, best case scenario, I'll have some spare plugs and a coil pack for down the road. I wanted a 2nd opinion, so I went back and started it up again, this time back to P0305.

 

[MAY03LT]

Damn my TB is slow to figure out what's wrong!!

I tried to get mine to turn on the SES light so I unplugged the number 2 coil and waited. It ran like crap for what seemed to be a really long time before it actually set the p0302.

If it tells me the same cylinder is having the issue, then I guess I'll have to look at the plug next.

When it's idling rough, try unplugging the number 5 coil and see if the rpms change.

 

[gmcman]

What cyl did the code show as the misfire......did it show #5?

Do you have all the vacuum lines connected, especially the large one under the top?

 

[RayVoy]

What cyl did the code show as the misfire......did it show #5?

this time back to P0305.

Post #12

 

[gmcman]

Post #12

I see the P0305 comment.......

I wasn't sure if the scanner would state a cyl# on a random misfire P0300.

 

[RayVoy]

I wasn't sure if the scanner would state a cyl# on a random misfire P0300.

No, that's why it's a random code...............


The P0300 will set when there are multiply mis-fires, when the newest code is different from a stored older mis-fire code, or, when the poor PCM is confused

 

[Blckshdw]

Got home from the amusement park with enough daylight to scarf down some pizza and tear down my intake again, and what do I find? They used the wrong damn plugs!!

They put some AC Delco 41-981 plugs in, instead!! Now honestly, it may not make too much of a difference, but due to the fact this happened 14 months after getting them replaced, it matters to me!!

The idle was 100x smoother in the parking lot, took it for a spin around the block, and it's back to it's punchy (for a LWB I6) self again. In the morning, I will be checking/replacing the other 5 plugs. I wonder if Advance Auto will let me return that coil pack or not? I could certainly use that $75 for something (meaning ANYTHING) else.

 

[gmcman]

No, that's why it's a random code...............


The P0300 will set when there are multiply mis-fires, when the newest code is different from a stored older mis-fire code, or, when the poor PCM is confused

Yeah, I understand the random bit....I wasn't exactly sure if the ecm detected a random misfire, that there would be the chance the ecm could narrow down the cyl #.

When my #4 took a dump, obviously I had an 0304 code but that was a dead coil.
I didn't remember before that if I had randoms or not.....been awhile.

 

[MAY03LT]

They put some AC Delco 41-981 plugs in, instead!! Now honestly, it may not make too much of a difference, but due to the fact this happened 14 months after getting them replaced, it matters to me!!

Weren't the 981s discontinued a few years back? I'm wondering if they were replaced at all.

 

[Blckshdw]

Weren't the 981s discontinued a few years back? I'm wondering if they were replaced at all.

No idea, I was hoping to see some Bosch plugs, or some other brand, and kinda had a bit of a let down when I saw the AC Delco, until I noticed the part number was different. At least it was something easy, and not degraded/damaged wiring of some sort. That would have been a royal pain.

 

[Mooseman]

Basically, these plugs are the original ones that came with your truck:

Thank you for writing ACDelco, John.
We appreciate your e-mail regarding the spark plug for your 2002 Chevrolet
TrailBlazer. Please know the 41-965 and 41-981 spark plugs have been
discontinued.
Be aware the 41-103 Iridium spark plug is the recommended spark plug for
your vehicle....

So, they never changed them. Explains the random misfire too.

 

[Freddy G.]

I am actually doing the job right now and kinda stuck. I as well pulled lout the first plug to find the same thing BLKSHDW did. Now my question is, I have a Gapping tool and I notice the gap is different from the plugs I have in now to the New Ac Delco 41-103's I bought. I do not know the mechanical Terminology to use but the tip of the plug looks different to me. I do not see like the needle tip on it like the new Ac Delco 41-103 has. I know gapping is suppossed to be the same or is it? Do these new Plugs come pregapped? Do I just take them out of the box and screw them right in?

 

[Blckshdw]

Yeah, you can drop the new plugs right in

 

[RayVoy]

They put some AC Delco 41-981 plugs in, instead!! Now honestly, it may not make too much of a difference, but due to the fact this happened 14 months after getting them replaced, it matters to me!!

Ya know, plugs will fail, and that maybe all that happened here.

I don't know anything about the shop you used, but I have ALWAYS used the number on the plug I pulled out to find a new one (sure, if I was buying them the day before, I'd look up the number at the store and get the newest plugs), this maybe what the shop did 14 months ago; pull the plug, look at number, go to stockroom get the plug with the same number.

But, let's be real, the old number plug worked just fine when the truck was new, it just did not have the capacity to be reliable for 100k miles (or, maybe the new plug is made cheaper and priced higher), that is probably why it was updated

I wonder if Advance Auto will let me return that coil pack or not? I could certainly use that $75 for something (meaning ANYTHING) else.

Is the new coil still on the truck? You may still need a coil...........sometimes when the plug fails, it will take the coil with it.

If you did change the coil, and the truck works, clean it up and take it back

 

[Blckshdw]

Well I'm back to square one. After running fine last night, and for a good portion of the day, I was on my way home from Clearwater and the idle became rough. Shortly after that, flashing CEL. Made one stop on the way home, and sure enough, when I restarted the engine, P0305 again.

Ray, hopefully you're right and the coil I put back in, is indeed bad. I'll try the new coil on the new spark plug and see if that helps any.

 

[Blckshdw]

Well, after 13 miles of city driving (mixed main roads and side streets) everything is running normally. One thing I noticed this morning, when things were good, was my higher MPGs was back. I was doing 75 on the freeway, and instead of getting 16mpg on the Scangauge, I was just under 20mpg :wootwoot: This is what I was getting when I first bought it (the Scangauge). During this last test run, I tallied 19.2 mpg for the trip. Considering the length of my drive earlier today before it failed, I'll reserve judgement until I make the morning and evening commute tomorrow with no problems.

 

[gmcman]

I know you don't want to hear this, but anything ignition related....with possibly the exception of spark plugs....I would always purchase from the dealer. I would even say anything electronic mainly sensors get it from the dealer. I lost hope in aftermarket after numerous crank sensor duds and coil pack duds on my grand am. Everything I purchased from the dealer worked.

 

[Blckshdw]

I know you don't want to hear this, but anything ignition related....with possibly the exception of spark plugs....I would always purchase from the dealer. I would even say anything electronic mainly sensors get it from the dealer. I lost hope in aftermarket after numerous crank sensor duds and coil pack duds on my grand am. Everything I purchased from the dealer worked.

If a dealership was within walking distance from home, I would have considered it. We'll see how this combination plays out. I didn't have the aftermarket coil in the truck for more than probably 5 minutes with the engine running before swapping it again tonight. Nothing like rush hour traffic to put things to the test right? Hoping I didn't cut too much off the life of my cat though during the drive home this evening...

 

[Sparky]

I know you don't want to hear this, but anything ignition related....with possibly the exception of spark plugs....I would always purchase from the dealer. I would even say anything electronic mainly sensors get it from the dealer. I lost hope in aftermarket after numerous crank sensor duds and coil pack duds on my grand am. Everything I purchased from the dealer worked.

I wouldn't go that far.

I'd stick with OEM AC Delco stuff, but why pay dealer ripoff prices? I'll go somewhere like Rock Auto for the same exact part and save a few bucks personally.

 

[jimmyjam]

whew... thats good...
i'll keep my eyes open in the junk yards for spare coil packs, just in case...

 

[gmcman]

If a dealership was within walking distance from home, I would have considered it.

Yeah....that would be a deal-breaker for sure.

 

[gmcman]

I wouldn't go that far.

I'd stick with OEM AC Delco stuff, but why pay dealer ripoff prices? I'll go somewhere like Rock Auto for the same exact part and save a few bucks personally.

Agreed. Luckily I haven't really needed to explore elsewhere for OEM but if the price becomes drastic then RockAuto is definately an option. The few things I have needed haven't been terribly expensive.

 

[jballentine]

My truck is having a issue where it seems like it's going to stall. Then it's back up to normal rpm. It does it just after start up & normal after it's up to temp, Starts just fine no issue cranking over. No codes are showing for misfire, New plugs, cleaned throttle body and checked it for any vac leaks. I'm stumped on what to look for next, I even had the dealer look at it they are not sure either. Any help where to start looking at next?

 

[Mounce]

My truck is having a issue where it seems like it's going to stall. Then it's back up to normal rpm. It does it just after start up & normal after it's up to temp, Starts just fine no issue cranking over. No codes are showing for misfire, New plugs, cleaned throttle body and checked it for any vac leaks. I'm stumped on what to look for next, I even had the dealer look at it they are not sure either. Any help where to start looking at next?

Happens to me too and I've seen other members post about it. Kinda seems like a normal thing that can't be fixed even though it's undesirable.

 

[Capote]

I experience the same, I know my alternator may be going bad, which might be the reason for the drop in RPM's and Voltage decline as well. Maybe replacing your coil packs? I replaced one of mine and the issue got a lot better.

 

[Mounce]

I wouldn't advise replacing coil packs unless a code arises and you can determine that it is a coil pack. It'd suck to spend hundreds of dollars on coils only to have the problem continue.

 

[jballentine]

Yeah I'd only replace coils if a code comes up. No sense of replacing them if that's not causing the intermittent studder i call it.

 

[jballentine]

Today it stalled out on me at a red light.

 

[Texan]

Is your TB a I6 or V/8? Your profile got lost in the transfer to the new system.
Did you remove the throttle body and clean the back side? Reset the ecm?