Rough idle/ shuddering in idle.

[iboughtatahoe23]

If you buy plugs, check the gaps. They say you don’t have to gap them but almost every one of my AC Delco plugs I bought from Rockauto were gapped at like 15-20, instead of 40. They tell you to return them and purchase new ones but that might take a while, with how many are not correct.

And you can get a gapping tool? Like at an auto store?

 

[iboughtatahoe23]

We had a 2002 flex fuel surburban and when I used E85 it was hard starting and I could tell the starter and battery wouldn't last near as long so I only occasionally ran it.

Hmmm. I don’t notice a difference in starting. I know they aren’t new (battery in alternator in my 2014 Tahoe)

I will get “starter lag” only on the first start of the day (sometimes)

It’s like it will skip or something but it always turns over and the crank isn’t slow. The crank just stutters or something sometimes. And this is only if it’s the first start and or if it’s cold. The battery usually hovers around 14.0V

 

[iboughtatahoe23]

Hmmm. I don’t notice a difference in starting. I know they aren’t new (battery in alternator in my 2014 Tahoe)

I will get “starter lag” only on the first start of the day (sometimes)

It’s like it will skip or something but it always turns over and the crank isn’t slow. The crank just stutters or something sometimes. And this is only if it’s the first start and or if it’s cold. The battery usually hovers around 14.0V

In reference to running e85

Wonder why that would happen for you with e85…. The slow starting?

 

[iboughtatahoe23]

Tahoes are one of the most heavy vehicles on the road, and slow as balls because of it but once they get up to speed its like riding on a cloud and that's where they shine.

The nearest freeway onramp near my house is a 20mph cork skrew onramp and I nearly get ran off the road every time I need to use the freeway because I have like less than 1 football field to get from 20mph to 70mph merging speed after the cork screw and sometimes the semi trucks don't have room to move over for me.

Ya not happening in our boats

 

[iboughtatahoe23]

We had a 2002 flex fuel surburban and when I used E85 it was hard starting and I could tell the starter and battery wouldn't last near as long so I only occasionally ran it.

Wondering how this would happen. And wasn’t aware they did flex fuel in 2nd gens… maybe I stand corrected? Thought it was only 3rd gen and up

 

[iboughtatahoe23]

I’ll keep adding to this thread about my idle as I keep running e85 consistently

 

[Fless]

In reference to running e85

Wonder why that would happen for you with e85…. The slow starting?

An informative read: https://eflexfuel.com/us/blog/do-cars-using-e85-start-in-the-cold

Keep in mind that the models with the virtual sensor may not be reading the alcohol content correctly, and may not apply the correct fuel table.

 

[Onlyone]

And you can get a gapping tool? Like at an auto store?

Yes. There’s a coin type that looks like it has a keychain hole but it’s actually where you can bend the tip without touching the delicate parts. Don’t use the Slide part to gap, only to check the actual gap. Use the little hole to widen the gap.

 

[OR VietVet]

Yes. There’s a coin type that looks like it has a keychain hole but it’s actually where you can bent the tip without touching the delicate parts. Don’t use the Slide part to gap, only to check the actual gap. Use the little hole to widen the gap.
View attachment 403334

They have stacks of those at AZ stores.

 

[Meathead16]

I admittedly didn't read through all the posts so this may have been mentioned but how's your motor / trans mounts?

 

[iboughtatahoe23]

I admittedly didn't read through all the posts so this may have been mentioned but how's your motor / trans mounts?

Not sure! Not familiar of the location of them

 

[Meathead16]

Pop your hood and shift from park to reverse, drive, then reverse and back to park. Watch the engine movement. Give the engine a couple snap throttles too while watching. If it moves fore or aft more than an inch (I think that's the general guideline) then it's time for mounts.

 

[iboughtatahoe23]

I know people were getting confised with my threads so I won’t make a new one as it’s still pertains to this issue:

Question:
Iridium plugs and premium wires worth it?

‘14 Tahoe 167k miles no idea last time plugs and wires were done. I’ve been debating on replacing both. Trying to fix rough idle. Engine mounts look good at a glance, throttle body was cleaned, idle pulley and serpentine belt and oil change so far.

My question is, Can I cheap out and at least go economy for the wires? Or should I just buy once cry once and get all the good stuff. (AC Delco wires and plugs recommended by Chevy)

 

[abrasumente]

Buy once cry once. I did. But get a scan tool first. Get a VxDiag off amazon for a buck fifty and dust off that old windows 7 laptop in your closet or find one for sale locally. Beats waiting for a Tech2 clone to get here on the boat.

After I changed my motor out, I had a slight miss that was getting on my nerves, same symptoms you're describing- I could see the tach bouncing from it, only happened in park or at idle, but it wasn't enough to set a CEL. Turns out one of the coil packs were bad. That vxdiag scan tool showed misfire counts that would go up and down on one coil. Since it was a junkyard motor with 140k on it that sat for god knows how long, I changed the bad coil, and did all the plugs and wires with OEM parts. Thing runs like a sewing machine now.

Those coils are $$$$. Usually with work like this I'd swap em all but that's $700+ in just coils, so I'll just wait for the next one to die. I'd recommend buying the OEM stuff, including the iridium plugs.

 

[iboughtatahoe23]

Buy once cry once. I did. But get a scan tool first. Get a VxDiag off amazon for a buck fifty and dust off that old windows 7 laptop in your closet or find one for sale locally. Beats waiting for a Tech2 clone to get here on the boat.

After I changed my motor out, I had a slight miss that was getting on my nerves, same symptoms you're describing- I could see the tach bouncing from it, only happened in park or at idle, but it wasn't enough to set a CEL. Turns out one of the coil packs were bad. That vxdiag scan tool showed misfire counts that would go up and down on one coil. Since it was a junkyard motor with 140k on it that sat for god knows how long, I changed the bad coil, and did all the plugs and wires with OEM parts. Thing runs like a sewing machine now.

Those coils are $$$$. Usually with work like this I'd swap em all but that's $700+ in just coils, so I'll just wait for the next one to die. I'd recommend buying the OEM stuff, including the iridium plugs.

Ok dang, I just ordered all new AC Delco plugs and wires for a little over $100 for all of it, also my starting the car has been kinda weird lately. Starting seems to lag or bog down sometimes. But will start fine.

Are you saying I might need new coil pack ? Thats not good. That sounds expensive.

 

[iboughtatahoe23]

Buy once cry once. I did. But get a scan tool first. Get a VxDiag off amazon for a buck fifty and dust off that old windows 7 laptop in your closet or find one for sale locally. Beats waiting for a Tech2 clone to get here on the boat.

After I changed my motor out, I had a slight miss that was getting on my nerves, same symptoms you're describing- I could see the tach bouncing from it, only happened in park or at idle, but it wasn't enough to set a CEL. Turns out one of the coil packs were bad. That vxdiag scan tool showed misfire counts that would go up and down on one coil. Since it was a junkyard motor with 140k on it that sat for god knows how long, I changed the bad coil, and did all the plugs and wires with OEM parts. Thing runs like a sewing machine now.

Those coils are $$$$. Usually with work like this I'd swap em all but that's $700+ in just coils, so I'll just wait for the next one to die. I'd recommend buying the OEM stuff, including the iridium plugs.

My funds are limited, especially after these wires and plugs , is there anyway I can diagnose anything with the scanner I have? Just an obd2 ?

 

[abrasumente]

My funds are limited, especially after these wires and plugs , is there anyway I can diagnose anything with the scanner I have? Just an obd2 ?

Most likely not, unless it sets a CEL. What you CAN do is buy one OEM coil pack for $80+t/s from Rockauto and swap it one at a time in place of the installed coils until the issue disappears. If funds are REAL tight, roll the junkyard dice and get a used coil pack. It might be bad too, but the odds are in your favor there. I feel if it was more than one bad coil it would probably set a multiple random misfire.

If you're having starting issues and weird running issues, I'd check your grounds- make sure they're tight and on bare metal, and the battery isn't old or crap. Just because it starts or shows 12.8 volts doesn't necessarily mean it's any count. Do a load test on it and see what the voltage drops to. I would do this before spending another dime, as it's free.

Story time:

I had a 93 cadillac I bought from a guy for 300 bucks several years ago, dude said the car would drive great for hours, days, weeks, months- and without rhyme or reason it would just start idling like crap, or die in traffic, or not start after sitting for a few days. Sometimes several times in a row, sometimes not for two months. He was tired of messing with it after firing the parts cannon at it to the detriment of his patience and wallet. I drove it home and poked around at it on and off over the span of a month, found a bad motor to body ground. I redid all the main battery wiring, and then drove it problem free for two years until some module caught fire in the dash and I sold it to a scrap yard.

 

[iboughtatahoe23]

Most likely not, unless it sets a CEL. What you CAN do is buy one OEM coil pack for $80+t/s from Rockauto and swap it one at a time in place of the installed coils until the issue disappears. If funds are REAL tight, roll the junkyard dice and get a used coil pack. It might be bad too, but the odds are in your favor there. I feel if it was more than one bad coil it would probably set a multiple random misfire.

If you're having starting issues and weird running issues, I'd check your grounds- make sure they're tight and on bare metal, and the battery isn't old or crap. Just because it starts or shows 12.8 volts doesn't necessarily mean it's any count. Do a load test on it and see what the voltage drops to. I would do this before spending another dime, as it's free.

Story time:

I had a 93 cadillac I bought from a guy for 300 bucks several years ago, dude said the car would drive great for hours, days, weeks, months- and without rhyme or reason it would just start idling like crap, or die in traffic, or not start after sitting for a few days. Sometimes several times in a row, sometimes not for two months. He was tired of messing with it after firing the parts cannon at it to the detriment of his patience and wallet. I drove it home and poked around at it on and off over the span of a month, found a bad motor to body ground. I redid all the main battery wiring, and then drove it problem free for two years until some module caught fire in the dash and I sold it to a scrap yard.

I did load tests on the battery and alternator around a month ago. They checked out. And you really think the coil packs Are bad? I dont have any codes? I know you said it’s possible to have misfires without codes. What is a miss fire symptoms?

I think I will start at plugs and wires and go from there


Good idea on the grounds. I’ll have to learn where All grounds are on mine. I know there’s a few on the engine.

What’s a good ground look like?

 

[abrasumente]

I did load tests on the battery and alternator around a month ago. They checked out. And you really think the coil packs Are bad? I dont have any codes? I know you said it’s possible to have misfires without codes. What is a miss fire symptoms?

I think I will start at plugs and wires and go from there


Good idea on the grounds. I’ll have to learn where All grounds are on mine. I know there’s a few on the engine.

What’s a good ground look like?

I think it's possible ONE of them could be bad. So in the ECM programming, there's a threshold that has to be met for misfire counts on a given cylinder/coil pack before it will set a check engine light. I don't know what that threshold is, but I can tell you from recent personal experience you can have a misfire without it turning the light on.

The symptoms you describe in your first post are almost IDENTICAL to what I experienced after I dumped that motor in the suburban, save that my truck would also misfire while sitting at a red light. It was definitely more noticeable when in park, it would be easily missed in drive if I hadn't worked on cars for 20 years. But look, I thought I was trippin at first, because even when sitting in park it was barely there. I'm used to cars either running so terrible you KNOW something's up, or the engine controls are so sensitive that when a gnat farts near your mass airflow sensor it turns your dash into a christmas tree. I'm like, there's no way it's misfiring. It would set the light if it was. Maybe I didn't tighten the manifolds up enough, maybe this junkyard motor has a bad valve seat, maybe it's a bad mount, maybe I'm just getting old. So, I bought that vxdiag tool off Amazon because I didn't want to wait for a Tech2 clone to get here from China.

So what it showed was that on cylinder 4, I had low double digit misfire counts. I forget exactly how it shows it in the Tech2 emulator but it's a real time data output from each coil pack. I had 7 coil packs sitting at 0 misfires, and cyl 4 would get to like, 15 misfires, and drop back down to 0, go to 12, drop down etc. I could watch the tach just BARELY seesaw in time with what I was seeing on the tool. So I put a new coil pack on that cylinder and since then this has been the smoothest running motor I've ever had.

I do wanna be clear, this may not necessarily be your problem. You could have something wonky going on with the cylinder deactivation. Worn cam lobe. Bad gas. Previous posters have talked about running premium regardless of if you're tuned or not, and I agree with them. The 5.3L LC9 in my burb has a 9.5:1 compression ratio, which should see at least 90 octane. I use 93. You CAN run 87 in them, the ECM will just pull timing. Keep in mind it's not about "will it run better" but more "will it run optimally". Higher octane=resistance to detonation. As long as you're not filling up at the country gas station out in the middle of nowhere, odds are you're getting good quality gas. Running E85 vs premium is moot around my parts- taking into consideration the higher consumption with E85 I spend the same money. BUT E85 also has a higher octane rating than premium, something like 100 if I remember right.

Put your plugs and wires in and see how it runs then, and report back.

 

[abrasumente]

Good grounds look like clean, tight crimps on their O ring terminators secured to shiny metal with a tight bolt. If you use a new spot for your ground, put dielectric grease or some other conductive protector on the metal so it doesn't rust.

We have ground straps on our trucks too, they look like braided wire. They serve the purpose. If you have one that's frayed or partially cut, I'd replace it with welder cable. Beats the price of car audio wire (which is what I used to use)- these days they wanna tell you the reason why their 2ga OFC wire is 40 bucks a foot is because it's 100% organic free range copper and the electrons flow smoother because they talked to the wire in a soothing voice while the machine put the insulation jacket on it.

There are grounds on the front passenger head and the rear driver side head to the firewall. I think there's another spot on the driver side of the block, right in front of the motor mount.