Weird off idle stumble/miss

[ghunt81]

Last week I drove my car on Monday and it drove fine, but I had to park it in the garage the rest of the week and was gone over the weekend, so I disconnected the battery.

I reconnected the battery and got it out yesterday and the idle just sounded off but thought maybe I was just imagining it. Today I drove it to work and something is definitely off. The idle sounds a little bit different and there's definitely some kind of a stumble or miss right as you come off idle, I can feel it and hear it.

What do I need to look at? I changed the plugs to Autolite HT1's last winter and it has been running great up until today. I'm going to pull the coil packs and make sure the plugs are tight and/or pull them and see if I see anything unusual but I'm not really sure what would be causing that. Runs perfectly fine through the rest of the RPM range as far as I can tell and I'm not getting a trouble light.

 

[Dino Dino Bambino]

Have you scanned the ECU for codes?

 

[Rick Simons]

Last week I drove my car on Monday and it drove fine, but I had to park it in the garage the rest of the week and was gone over the weekend, so I disconnected the battery.

I reconnected the battery and got it out yesterday and the idle just sounded off but thought maybe I was just imagining it. Today I drove it to work and something is definitely off. The idle sounds a little bit different and there's definitely some kind of a stumble or miss right as you come off idle, I can feel it and hear it.

What do I need to look at? I changed the plugs to Autolite HT1's last winter and it has been running great up until today. I'm going to pull the coil packs and make sure the plugs are tight and/or pull them and see if I see anything unusual but I'm not really sure what would be causing that. Runs perfectly fine through the rest of the RPM range as far as I can tell and I'm not getting a trouble light.

That's interesting; I had a similar situation. The engine would just go flat at cruising speed, and the AFR gauge showed it to be full lean. Lifting the pedal then putting it back and it was fine again. Looked it when I got home and found a leak between the MAF sensor and the mounting pad on the CAI. Put the stock intake on with a matching tune and ran around like that for a few months. Put the JLT CAI back on with tis tune and had the same issue as you; if the throttle was opened too far from idle I would get a stumble and sometimes a backfire. Put the stock airbox back on and haven't had time to mess with the CAI since.

 

[ghunt81]

I hooked up my little handheld code scanner but it shows nothing, I may have to try with my sct.

My first thought was a possible vacuum leak as well but a quick look didn't find anything. I'll have to take the cai off and check it all over.

Just seems odd since it was running perfect last week.

 

[Juice]

Battery disconnect cleared adaptive memory.
Your tune is off a small amount. PCM should relearn.
This is why I prefer a trickle charger.

 

[ghunt81]

I guess, except I've been disconnecting the battery every time I park the car because it has a bad habit of drawing the battery dead after a week-ish and I never know how long it's going to sit. So yeah I've probably had the battery disconnected like 20 times already this year and never had this issue before.

 

[Juice]

I guess, except I've been disconnecting the battery every time I park the car because it has a bad habit of drawing the battery dead after a week-ish and I never know how long it's going to sit. So yeah I've probably had the battery disconnected like 20 times already this year and never had this issue before.

Well, thats new info.
Dead batt in a week isnt right. Mine will kill the battery in 6-8weeks. Will start, but clock resets.
So, do you leave the key in the ignition when stored?

 

[ghunt81]

I know it's not right, it's something that it just started doing in the last couple of years and I'm not sure why since I haven't added any new electrical accessories except my Raxiom taillights. No I do not leave the key in it. I just know it ruined my old battery by drawing it dead so many times, I got a new battery and don't want to kill this one as well. I don't know exactly how long it takes but I know it will run it so dead that the interior lights won't even come on.

 

[crjackson]

I know it's not right, it's something that it just started doing in the last couple of years and I'm not sure why since I haven't added any new electrical accessories except my Raxiom taillights. No I do not leave the key in it. I just know it ruined my old battery by drawing it dead so many times, I got a new battery and don't want to kill this one as well. I don't know exactly how long it takes but I know it will run it so dead that the interior lights won't even come on.

It might be time to dig in, and repair the root cause. This type of thing would really annoy me personally.

 

[Windstang]

Time to do a parasitic draw test to find the problem. I assume you have the Shaker 500 radio. Apparently they are know as a battery killer after a while when they go bad.

 

[Juice]

^^^ That, or the sjb isnt going to full "sleep". I know I have seen my park lamps blink on for a second. Car was in driveway, been off and key out for about 20 min. It was dusk. I was sitting in front of the car working on something. My park lights blinked on for a sec.. Never seen it do that before or since (but didnt look for it either)
Point is, the sjb was doing something with the car off. Im guessing that is when the sjb went to "sleep".

 

[ghunt81]

Alright so...last weekend I pulled off the CAI, everything looked good except the hose going from the passenger side of the tube to the cam cover kinda looked like it had a tear in it, and it was pretty old anyway, so I replaced it. Pulled all the coil packs, the plugs were all snug but I did not remove them. Wasn't sure what else to look at.

Drove it to work today and I can't tell if it feels slightly better or if it's just a placebo but it is still doing the same thing. Seems to be confined below 1500 RPM, I can feel it stumble coming off idle and it certainly sounds like a misfire, and then above that it is perfectly normal. Really weird.

BTW- I'm not particularly concerned about the battery drain right now as I have other problems to deal with first, but it probably is the shaker 500 doing it.

 

[06 T-RED S/C GT]

If you know for certain it's not your plugs? Check your coil boots to make sure there are no signs of any cracks

 

[ghunt81]

It shouldn't be as the plugs are brand new but I will probably pull them and check.

When you say cracks, where would the cracks be? On the silicone boots themselves or another part of the coil packs? I didn't see anything obvious when I had the coil packs off but I only looked at the bottom of the boot where it goes onto the plug.

 

[Pentalab]

Did u gap the plugs correctly ? Any scanner, like my aeroforce gauges, plugged into the OBD port will show total misfires. (resets to zero with eng off).

I had a similar issue with excess current draw, with eng off, on my old Honda. I had to insert a DVM (in DC current mode) in series with every electrical device in the car. The easiest way to do this is to remove the fuses, one at a time, and temp put the DVM probes across the fuse terminals. There should be no current, none on any of the fuse positions...except for the passive ignition alarm setup.

For an initial fast check, disconnect the negative terminal of the battery, and insert the DVM (in dc current mode), between negative of battery terminal..and negative of the disconnected battery cable.

 

[06 T-RED S/C GT]

It shouldn't be as the plugs are brand new but I will probably pull them and check.

When you say cracks, where would the cracks be? On the silicone boots themselves or another part of the coil packs? I didn't see anything obvious when I had the coil packs off but I only looked at the bottom of the boot where it goes onto the plug.

Examine the silicone boots thoroughly.. If there's even a small hairline crack? it will cause your engine to misfire.. Check the boots from top to bottom, not just the bottom!

 

[ghunt81]

I did not gap the plugs because they are the ground strap type and said right on the box to not gap them.

 

[Pentalab]

I used Br

I did not gap the plugs because they are the ground strap type and said right on the box to not gap them.

I used Brisk plugs. For NA cars, they have to be gapped at .060"...( same as oem plugs in a NA 4.6). With my small Roush M90 blower, ( 5.7 psi boost), they are gapped at .035". With 8-9 psi boost, the gap is reduced to just .032". At just over 10 psi boost, one step colder plugs are used.

When I installed the new Brisk plugs into my 2010 4.6 eng, the misfires dropped to zero.

 

[crjackson]

I did not gap the plugs because they are the ground strap type and said right on the box to not gap them.

I hope you at least checked/verified the gap before installing. They’re probably okay, but I would have checked. I’ve found the so-called pre-gapped plugs are gapped wrong out of the box sometimes, but I don’t the plugs with the looped electrodes. You should always check plug gap however.

Mine are gapped at 0.032 as well since I’m boosted.

 

[DieHarder]

I'd try replacing the plugs. Easy elimination step. Went with the Brisk plugs myself. True one-piece; a bit expensive but after dealing with broken plugs they're cheap insurance in my book. Gapped at 0.032 like the gent above (also FI). I also replaced the stock coils recently w/OEM units. Doing that actually improved idling slightly; not that the old ones were acting up terribly but figured being 15 years old it couldn't hurt.