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Intermittent Rough Idle?

30K views 51 replies 23 participants last post by  RatherNotSay 
#1 ·
I've been experiencing some intermittent rough idling. I noticed it first yesterday on my way to a friend's house after being dyno'd. I did, just a few days ago, install NGK Iridium IX's (ZFR6AP-11) 1-step colder plugs only a few days ago however I haven't had any idling problems until now.

I don't know if dynoing it (taking the car to the top of 4th gear for the first time ever) had something to do with exasperating an underlying/existing problem but I certainly notice it now.

The RPMs at idle usually sit around 690-700, however sometimes it starts to dip and bounce back and forth between the high 500's and 700- until, after several seconds it levels itself out. If I wait long enough it'll happen again.

I took a short clip with my iPhone with it occurring:
http://www.gmelliottvideo.com/roughidle.MOV


I'm assuming this is directly related to my recent plug install after MS1 went in. I read that some didn't run right with ZFR's and went with the BKR6EIX with better results. Would there be any reason for the ZFR's to be causing this? Maybe I damaged one or more of them gapping them- we really didn't have good tools to do it.
 
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#2 · (Edited)
I've been experiencing some intermittent rough idling. I noticed it first yesterday on my way to a friend's house after being dyno'd. I did, just a few days ago, install NGK Iridium IX's (ZFR6AP-11) 1-step colder plugs only a few days ago however I haven't had any idling problems until now.

I don't know if dynoing it (taking the car to the top of 4th gear for the first time ever) had something to do with exasperating an underlying/existing problem but I certainly notice it now.

The RPMs at idle usually sit around 690-700, however sometimes it starts to dip and bounce back and forth between the high 500's and 700- until, after several seconds it levels itself out. If I wait long enough it'll happen again.

I took a short clip with my iPhone with it occurring:
http://www.gmelliottvideo.com/roughidle.MOV


I'm assuming this is directly related to my recent plug install after MS1 went in. I read that some didn't run right with ZFR's and went with the BKR6EIX with better results. Would there be any reason for the ZFR's to be causing this? Maybe I damaged one or more of them gapping them- we really didn't have good tools to do it.
Did you reset your pcm after installing the spark plugs?
 
#3 ·
As in remove the battery? No- I'll give it a try though. How long should the negative be left off for the ECU to "reset"?

PS That video should be up shortly- just finishing cutting it!
 
#4 ·
As in remove the battery? No- I'll give it a try though. How long should the negative be left off for the ECU to "reset"?

PS That video should be up shortly- just finishing cutting it!
Thanks.....I would try 10 mins or so. I could not hear it at all. Maybe its my laptop but I got very low volume. I understand the stock plugs by design add more timing than the bkrs. Your pcm may have been compensating. Its just a guess.

Were you still at the dyno when my clutch took a dump? That was so disappointing. I'll tell you, the mechanic was getting real excited when we started seeing better numbers. I guess he wasnt expecting it and then again, neither was I.
 
#6 ·
it the drive by wire, mine does it as well.
after a 10 mile trip on the high way i let it idle the rpms jump up and down. mine did this after the ms1 install
 
#7 ·
So you only notice this after driving for a while (ie after it's hot)? When I felt it, it was indeed after some highway time.
 
#12 ·
yep, it only seems to be after a steady long drive.
 
#8 · (Edited)
Idk if it helps at all(coming from a non srt owner) but mine will also do that, but not as much. It will dip so low it seems like its going to die, and then flutters for a minute, and then everything is a-ok.

One thing is for sure, all this computer controlled, electronic garbage, is well... garbage..
 
#15 ·
My local dealership has asked a Chrysler Engineer to come and troubleshoot my car on Tuesday. Hopefully this can provide a more definitive answer to what is causing the RPM drop and fluctuation. A dealership Tech observed a similar idle drop and fluctuation on my car that you seem to describe. I asked if there was any sign of misfire and the Tech indicated that he observed nothing to indicate a problem with the injectors or plugs. The Tech recommended flashing the ECU. The ECU flash did not help the idle and the Technician is at a loss to explain why it is occurring. Has anyone noticed an accompanying knocking sound towards the rear of the engine when the idle drops low or fluctuates?
 
#16 ·
my car is practically stock and i get that also... I have just stopped paying attention to it altogether.. i can hear it in my exhaust.. but its just another part of this car i have to accept lol.
 
#17 ·
I noticed mine was dropping from ~650RPM to <500RPM the first day I woke her from her winter nap. Sounded like it was going to stall, then it recovered.

Filled her up with good premium gas and took it for a hard run on through town and on the hwy.
My case, it may have been dirty plugs as it was running really rich before hand. That helped in my case.
I'd say take it for a good run, then pull the plugs to see what they tell you.
 
#18 ·
Well, it did it to me again today. I think it may also have to do with temps. Today it's pretty warm in S.Jersey, 78 degrees. I took a 12 mile trip and when I got to my destination the idle was bouncing up and down between 500-700 rpms. The AEM WB showed it going rich when the idle dropped each time as well (though that could be the computer adding fuel to avoid stalling).

When the rpms dip (near or slightly below 500 I DO hear a feint knocking sound from the engine). But I presume that is normal from such a rough low idle. It kinda like when you don't give it enough gas when taking off in first.

Another thing I noticed is, in general, the car isn't very smooth at low speeds in first gear- for example driving around a parking lot. It's very jumpy.

I wonder what the cause for this is??? I'd be quick to say it's something to do with MPS1 but some have mentioned they've experienced this on their stock vehicles. I also though it may have to do with my plugs (NGK iridium 1-step colder) though- again, I'm not sure everyone has these that is encountering this issue. It's quite annoying becuase at stop lights after a long drive it feels like I'm driving a clunker. I can even HEAR the rpms in the exhaust rhythmically when it happens as well. :icon_flaming:
 
#21 · (Edited)
I dropped the car off at the dealership this afternoon. Hopefully when the Chrysler engineer helps troubleshoot with the Tech tomorrow morning it can provide an answer. Of course the problem is intermittent so maybe it wont do it. I find it happens more often during a prolonged idle like when I have to wait for a couple street light to changes. I personally thought the knocking sound was coming from the flywheel area.
 
#22 ·
mine just started doing this a lot worse today than ever before. im actually afraid to come to a complete stop. it is really warm today here, it hit 80.
my rpm dips below 500 then shoots up to 1000 and my a/f reads 10.0 then lean--- and just about shuts off. it just keeps bouncing back and forth and cant seem to straiten itself out.
and i noticed my tial bov seem to whistle a little as im coming to a stop, it only does this when its warm out. it sounds like its not closing all the way when im in vacuum.
the car seem to be fine when cruising.
 
#23 ·
soon as the temp got below 65 my car went back to normal, if you want to call it that.LOL
 
#28 ·
My car does it all the time where the idle starts dipping down low like that then bounces back and forth it usually only happens in warmer weather I havent noticed it at all during the winter. I've had the car actually stall a few times or I will try to go and then it stalls. Thats why I almost always have to rev me engine at a light when its warm otherwise it will stall.
 
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#29 ·
This could be a totally different issue then what I had experienced with the neon when the PCV valve host was cracked.
What the neon would do is idle erratically once it hit running temp. Before it hit that temp, the censors involved would not cause any issues.
The car would rev up or stall out. When the crack was minor, it would drop in RPM, and the car would then over compensate, bringing the RPMs back up above normal idle for a second or two. Then back and forth.

Now understanding these cars have a turbo, and a crazy computer, it could be something else. I would think that it would be something similar to the PCV valve, where there is a potential air leak, and something allowing the computer to monitor and try to compensate.
 
#30 ·
I think you are def on the right path because it does feel like the car is over compensating when it does that and it just keeps going back in forth. Should be interesting to find out. I just hit 30,000 miles on my car anythings possible.
 
#31 ·
85 degrees here in South Jersey (What happened to Spring?!)- anyway it was doing it pretty bad today. I'm tempted to switch back to my stock plugs but don't want to go though the trouble if it's something else.

My car has less than 2,000 miles on it but I did mod it (MS1, MPx catted DP, Needswings Intake, NGK iridium 1-step colder plugs).

I'd really like to get to the bottom of this sooner rather than later! :mecry:
 
#32 ·
The engineer analyzed the data and determined that the idle fluctuation on my car is a result of FAULTY FUEL INJECTORS. I haven't had a chance to get a more detailed explanation from the service manager. The new injectors are in transit and should be in the car Wednesday or Thursday. It seems strange because they did not behave like a typical fuel injection issue. I wonder if my MPG will improve or become more consistent.
 
#33 ·
i dont have stock injectors so i doubt thats the problem.
 
#34 ·
Well I bought a set of the BKR6EIX NGK plugs (currently I have ZFR5FIX's in there). I painstakingly and meticulously gapped them with a proper gapping tool (one that doesn't put pressure on the tip) all to .031.

I'm going to install them tomorrow along with anti-seize on the threads and dielectric grease on the boots. If this doesn't work maybe it's the fact that they are 1-step colder and I'll try the stock plugs which only had like 1,000 miles on them. I already pre-gapped them to .031 as well.

If THAT doesn't work I'll try upgrading the injectors (though I probably don't have enough boost for this). Newb Question: How do you install injectors...also if they are slightly larger than stock with they automatically put out more fuel or is that CPU controlled?
 
#35 ·
the injectors are easy, its really self explanatory once you start taking them out. the hardest part is putting the new injectors in the rail. i just put a little oil on the o-rings and slide them right in, its like a 15min install. make sure you wrap a rag around the fuel line before you disconnect it from the rail.

the injectors are controlled by the pcm. you really wont need bigger unless your clamped.
 
#36 ·
I was talking about getting new injectors to replace the possibly faulty stock ones. Though, as you said, you have aftermarket injectors and have the idle issue.
 
#37 ·
I have the same problem, the only time mine does is in hot temps with stop and go traffic and at the track usually after each run when I'm going to get back in line. It sounds like it's a heat problem, maybe when the fans come on it starts idling rough???
 
#38 · (Edited)
UPDATE: Well I changed my plugs this morning over to the BKR6EIX (previously had the ZFR5FIX's) . When I took my engine cover off I also noticed a crimp in one of my vacuum hoses. The one that comes out of the bottom of the catch can and up to the valve cover. Because it has to take on sort of an S-shape it ends up folding the line. I decided to NOT re-install my engine cover which allowed me more clearance to turn the catch can and cut about 1/2 and inch off the hose so that it wouldn't fold.

Anyway after that was all done I went out for a drive. Heated up the engine and came to a stop. It ran perfect! Reluctant to believe I had fixed it I kept driving it for another 10 minutes or so and stopped- once again it idled perfect! I was quite happy at this point and decided to turn around and start heading home. :bigthumb:

Well....at a stoplight on the way home I felt it do it again. Granted it wasn't as aggressive or long (it seemed to smooth out in a few seconds-while previously it would seemingly be caught in a idle bouncing loop and never recover.

So...NO the plugs did NOT fix it. I said screw it, rolled up my windows and turned on the AC- it doesn't do it with the 100 rpm rise with the AC on. :icon_flaming:

I wonder if it does have something to do with the fans turning on. Though I've never heard them running. Are they that quiet in this car?

I did some research on this issue on Google and found a bunch of Z owners with the same issue. They found on their cars it was the CHTS (cylinder heat temp sensor). Do you think it could be the same culprit on our cars?

I guess I could always put the stock plugs back in to test it and/or put the stock ECU in. However I really don't feel like going through the trouble. After all if I find the stock ECU solves the issue where does that leave me? I'm not going to go back to the stock ECU. Maybe the PTP tune if anything.

PS One interesting note- because I had the negative terminal disconnected during the plug install it reset my ECU, and what do you know the ESP/BAS light issue is back. lol Maybe the computer has to learn or something- because previous to this I hadn't seen it in weeks!
 
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