6g72 plug change..and now random drops small drops in idle

[8thLS6]

Had the same shop chamge my plugs today that did the first plug change for me since owning the car. I had ngk coppers in em since 2011 so no doubt I felt a change was needed, and went with Denso PK16PR11.

The car starts smooth, shifts smooth if not smoother, exhaust has a more consistent tone..all noticeable perks except a small drop in idle when I'm at the lights. Not enough to where the car feels like its gonna die, but you can see the needle twich a lil. And it doesn't happen a lot by any means. Say if I did about an hours worth of driving from the time I got the car back, it's only happened 3 times I can remember..and its no back and forth. Just a slight stumble and then picks itself up. Could it be the ecu adjusting to the fresh plugs and assuming better burn? I know it doesn't take much to get things out of whack. I've had similar results after cleaning my maf with maf cleaner or disconnecting my battery, and after about a day of driving its all good.

Just looking to get you guys take on the matter, before considering taking it back or waiting it out. Not like its smoking, dying or the needle is doing the harlem shake lol

[Silvertune]

It is 100% normal. In fact when it does that you know it's running quite well. Not sure exactly why they do it but it is a symptom I've seen on every single 3 liter with up to date maintenance that I've ever worked on and that's a pretty staggering number at this point. I believe it is simply the car testing to see if it can further drop the idle. My old 3 liter idled at 600 RPM's. Never died but it was so low you could hardly tell the car is on.

[DTP]

Can the same be said about the 64? Sorry to thread Jack

Sent from my SGH-I777 using Tapatalk 4 Beta

[8thLS6]

Interesting. Does it ever normalize itself? I took it out tonight after I made this thread, and I noticed every stop light it did it. No problems while moving or in park, other then it seemed the exhaust has more of a pulse to it, and seemed to a tad more than normal. Never could tell from in the car. But driving is so smooth..wasn't bad before but just better now. I did get the oil change as well if that makes a diff. QS defy, I like that stuff it more than mobil1 syn blend high mileage. Only two oils I've used since I owned the car. Also ran a small amount of mmo in the oil shortly before the change and some in the gas tank.

One more thing I had a service light prior to all of this. It use to come and go on its own. Now its constant..but sa me shop looked it up the first time and saw it was cat related, something about warm up. Seem to disappear and reappear only when I got gas, and when I ran mmo in it seemed to make it go away? Someone told me on here its probably the cat or o2 thats bad. Haven't bothered to get a 2nd scan since the shop charges $50! and advance autos scanner wouldn't even read

Thanks for the help..keep you guys posted if it changes

[thegalant]

any scanner from any where as long as it's obdII should tell you what that code is and most if not all places do it free.

[8thLS6]

yeah I made a post about it before, and someone said the typical scanner most autoparts store use (advance in this case), you kinda have to push it up good on the port to make a connection. The shop on the other hand doesn't have that problem, but for a $50 charge I can see why lol. But as far as the car, the drop in idle at the lights might be gone. I think the ecu might be getting use to things. I can still feel a slight movement now and then, but that could still just be me being over sensitive to the natural vibrations from the motor since I'm being cautious at the moment. However, it doesn't seem enough for the needle to drop as it clearly did the other day or the quick shake it does from it. I told the shop today about all of this, and if there's any issues still over the weekend I'm bringing it back Monday. Hopefully not though

[Silvertune]

I unfortunately have not dealt with any healthy four cylinders that were not modified in such a way that would mitigate the OP's symptoms. That said, I don't see why not. It's the same car, while the motors differ Mitsu's tuning algorithms had been the same for all of them.

Among other things, warm up catalyst codes are for a bad cat. Either the catalyst is coated or it's just plain worn out. If you end up replacing just remember to scrap your old cat if you can, I get $80 a piece for them up here so I bring in every one I can get my hands on (legally of course!).

As for the idle, it seems to come and go on the cars I work on. Even with cars that have manifold swaps and stock level engine swaps do it. All I figure is that the ECU is constantly learning and testing abilities against the data it compiles to make the car run as efficiently as possible. I know another thing that can make the idle fluctuate just a tad is when it runs the EGR. It has a duty cycle set that runs at idle under certain circumstances. I believe that may also be a contributor to it.

[8thLS6]

I unfortunately have not dealt with any healthy four cylinders that were not modified in such a way that would mitigate the OP's symptoms. That said, I don't see why not. It's the same car, while the motors differ Mitsu's tuning algorithms had been the same for all of them.

Among other things, warm up catalyst codes are for a bad cat. Either the catalyst is coated or it's just plain worn out. If you end up replacing just remember to scrap your old cat if you can, I get $80 a piece for them up here so I bring in every one I can get my hands on (legally of course!).

As for the idle, it seems to come and go on the cars I work on. Even with cars that have manifold swaps and stock level engine swaps do it. All I figure is that the ECU is constantly learning and testing abilities against the data it compiles to make the car run as efficiently as possible. I know another thing that can make the idle fluctuate just a tad is when it runs the EGR. It has a duty cycle set that runs at idle under certain circumstances. I believe that may also be a contributor to it.

Cool, and good idea on scraping the cats. I'll have to look into that if I replace it lol

[thegalant]

uhg! I've had a bad cat for a couple years now. I don't want to pay 400 bucks for a cat though... I haven't been able to find a used one any where, apparently there is a law about selling used cats... I almost got one and I stupidly asked if the precat came with and they wouldnt sell it to me after that!!! wtf!!! I had it in my hands...

[thegalant]

Spark plugs make a difference, I've found that ngk platinums dont last very long. But they give better fuel economy and I just bought the Denso u-grove iridium/rhodium plugs. KL16. The problem with those fine tipped plugs is that typically they run great right away but they suffer from erosion over time and the gap changes as that electrode erodes causing uneven gap and misfire. Thats why people recommend regular ngk R copper resisters because they are super durable. If you have any oil leaks into your plugs they will fade faster. The Denso's I've got have a .4mm electrode which is very small but they have the best plug in the market with a fine tip. NGK's don't have rhodium, denso's do. so blah...

[Silvertune]

I just picked myself up a set of .4 iridium denso's for my next block. Glad to know they have good feedback already.

[thegalant]

Here is what my platinums looked like after about 40k or 50k
click on the bottom right tab on the image to see exploded view. You will see 3and 4 did okay but 1 and 2 had gap fade causing misfire.

[IMG][/IMG]

[8thLS6]

Well never did come back for a visit that monday lol. Things seem to be a-ok and the car runs stronger with the new denso plats.