Idle Worse After Plugs and Wires, WWYD?

[Mickey_7106]

Not saying this is your problem, but i always use ngk iridium and i think i have 8mm or 10mm Taylor wires that are low 400 ohms range.

If i were in your shoes, i would put the old plugs back and run seafoam through a vacuum line, oil and fuel. Run about 200 miles and then disconnect battery so that it can relearn all tables, switch to new plugs, change oil, clean maf and tb. That usually clears up idle issues for me

 

[George B]

To flesh this out a bit. When I noticed this in my case I simply noted more slight and random idle misfires. I immediately connected the Tech2 and looked at the live misfire data only to find they weren’t showing up in the misfire data. I then sent a log to BBP and they provided my first tune file without noting any issues with the truck.

I did an Italian tuneup and moved on.

I haven’t thought about it again until James brought it up.

 

[Doubeleive]

double check the plugs and the hummer mount will cause some very slight vibration at idle
clean the intake, put some injector cleaner in it for a few tanks, 2 bottles per tank full.
it's .99 cents at wallyworld.

 

[swathdiver]

You said the motor mount is new. Is it the fluid filled OE type or the Hummer one?

The motor mount is another stock one, with the fluid! LOL It did not idle this way immediately before changing the plugs and wires.

The TB was cleaned afterwards, no misfires noted on the Tech-2 after several full power runs. Ran 2 bottles of Techron Fuel System Cleaner back in December, a couple of weeks before the plugs and wires were changed.

I built a nice big step to reach under the hood but it is still too hard for me to do for any length of time. Looks like I'll have to hire another kid to help pull the plugs and wires and check them all.

 

[gooffeyguy]

So did this start happening right after changing the plugs and wires or did it just start recently?

 

[George B]

So did this start happening right after changing the plugs and wires or did it just start recently?

For me it was immediately after the change.

 

[swathdiver]

So did this start happening right after changing the plugs and wires or did it just start recently?

For me it was immediately after the change.

Just like George, right after. I reckon it's not anything else other than plugs and wires, the only changes we made that day.

 

[YukonRog]

Same here and share the same sentiments. I kept the old plugs too, technically, they are at half life. The wires even ohmed out a little better than the ones I put on save for one that broke, which is what precipitated this whole thing.

Been buying up new 41-985s whenever I come across them, have 5 so far!

Thirty years ago we ran NGK Splitfires in our Buicks and they gave us about 5 horsepower at the cost of 3 mpgs over the stock plugs. I have not investigated alternate plugs.

5 hp! Was that ever proven on a Dyno? I remember when you had to change plugs every 5-10k. Now they're 100k rated. Does it smooth out with a small increase in idle? Could it be coincidence? How's the IAC? For me, a rough idling 5.3 is normal.

 

[petethepug]

Plug wires. Oh the plug wires. If they’re not removed with a tool that can grab them at the boot to remove them without pulling the lead, they’re toast. Do you think your helper put the wrong lead on and removed it to replace it on the correct bank?

I’ve toasted high end HT leads before and I had to learn that the car ran better with one 99¢ lead and three of the four $60 leads vs putting the expensive damaged lead back on.

I unknowingly damaged the lead and caused the misfire. The local shop was cool and gave warranty on a new set. If possible, buy another set of identical leads knowing you can return them if they’re not up to spec or damaged. Swap the leads one more time, one by one one and return the other set as damaged for a refund.

Always start the remedy in the “if it works don’t fix it” mindset by trying to put things back to how they were when they had no issues. In this case installing new leads and being 100% sure they’re not pulled on is one option that doesn’t require a Tech II

 

[gooffeyguy]

Copper plugs still need to be changed about every 10-15k miles.

Platinum plugs didn't come out till the mid 80s and were expensive. Iridium plugs came out in mid 90s