Hello,
My 2004 TL AT suddenly started stuttering at anything above light throttle, 20%ish. I also have codes P0301, P0304, P0306, and P0300. No recent changes to car, 4 days and 75+ miles since last fill up. Changed plugs 2-3 yrs ago with Autolite iridiums. I don't see anything obviously bad on plus or coils like arc tracing or significant discoloration. Any ideas would be appreciated. I hate to start doing swap-nostics. thank you

 

With those codes, I would start with the coils. Out may be just one bad, or more. Easiest way is to disconnect one at a time and see which one doesn't make a difference to the engine.

 

you got a bad coil. Start diagnosis by unplugging them one by one to hear which pack is causing your car to lose power. If it dips, it's good; the cylinder that doesn't change is bad. Then go buy a DENSO/NGK replacement one here: https://www.rockauto.com/en/catalog/...tion+coil,7060

 

Every coil makes a difference when I unplug them. Forgot to mention I had done that as well. That's not a guarantee they're good though is it?
Car starts fine. The idle is a little rough for the first 5-10 seconds, then cleans up. If I baby the throttle, it drives fine.

 

Unplug the IAC and try unplugging the coils again.

Anything else you forgot to mention?

Do you have a scanner or a way to see live data?

 

Nice to get such quick responses, thank you.
No I don't have a scanner. Been reading codes at Advance Auto. I bought a coil locally (couldn't get a NGK in town). I put it on each of the misfiring cylinders and test drove each time with the new one ending up on #1 . Little if any difference, hard to say for sure.
Cleared the codes, took a drive to set them again and got 300 304 & 306 confirmed and 301 pending. It was only a couple mile drive.
I tried the old carb cleaner trick around intake manifold and vacuum lines but didn't notice any change in idle.
I'm leaning toward either buying all new NGK plugs to rule them out or 2 more coils so all misfiring coils are new.

What do you all think?

 

I was going to unplug IACV and then unplug coils but I can't find it. Looking at Acuraoemparts, they only list that part up to 2003. Is that right?

 

SOLVED! Hey guys, the non NGK plugs were nagging at me even though the Autolite Iridiums had been in there working fine for over 20,000 mi. I installed them today and car runs great now! I hate subscribing to the theory that you "MUST" use a specific brand of plug to make a car run properly but 20k out of a set of iridums isn't very impressive.
If someone else is having the misfire problems I was experiencing, don't discount the plugs no matter how old they are.

Again thanks for everyone's input.
I'd still like to know if this model has an IAC valve that El Cheapo mentioned cause I sure as hell can't find it.

 

My mistake. I was sure it had one like the other J-series engines, but after some reading it looks like it does not have one. The idle is controlled electronically by the PCM.

 

Use only Denso or NGK iridiums. In fact, just stay away from NGK since they are copied all over the place.

 

unfortunately buying these products from ebay and other discount online retailers is a gamble. I stick to local auto stores, use their 25% off coupons amd know I'm getting what the label says.....hopefully lol

I wouldn't purchase anything named Autolite. Plugs were probably $3.99