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Old 07-27-2009, 01:45 AM   #1
DXO
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Default Rough Idle

Back about 6 months ago I installed MS on my car. Took my time double checked everything. When I first cranked it, it ran fine. Not great, but fine.
I have tried for months to get it to smooth out but my newest upgrades, injectors and straight-pipe exhaust, didn't help at all.

I have checked timing, over all and the cam gears. At idle I have seen people running anywhere between 10* and 18* advance but I can't get my RPMs below 1100 anywhere in that range. not to mention my AFR any better than 13.9.

After installing MS on my second car, a Nissan 240sx, I see how smooth it idles and want my Miata the same. I'm tired of this rough idle. ANY ideas would be appreciated.

Here are my latest msq files and a log of the car at idle.
2009-07-26_23.40.08.msl
2009-07-19_14.25.43.msq

Last edited by DXO; 07-27-2009 at 01:56 AM.
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Old 07-27-2009, 02:38 PM   #2
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I was going to suggest making sure you run hi-res, but it looks like you are.

It will typically idle smoother closer to 10* than 18*, but your 12* should be fine.

I see from your VE table that you've got some richer values in a 19 kPa row down near idle rpm. If your typical MAP at idle is 19<MAP<24 then it's going to idle really weird because of the different values you have in the 19 kPa row compared to the 24 kPa row. Basically you're leaving MS quite a bit of room to interpolate, so it will fluctuate a lot. I took my typical MAP at idle and have two rows of kPa with identical VEs bracketing that range. So I have cells at 24 and 30 kPa, and 700 and 1200 rpm (four cells encompassing the typical idle range on my car of 26-27 kPa and 800-900 rpm) all with identical VEs. When you adjust the table to be richer or leaner at idle, keep all four of those cells at the same value. You could try that and see if it idles smoother.

I haven't installed my 550s yet, but my impression from reading the forum is that a few people with larger injectors idle a bit richer or a bit higher rpm so your case doesn't seem too unusual from that standpoint. But it shouldn't be rough; that needs to be fixed.

I also see your AFR target table is 13.1:1 everywhere out of boost, so if you run EGO it will be pretty rich all the time. Your fuel economy will suck *****, for one. I see you have EGO enabled over 1600 rpm so it shouldn't be affecting your idle, but you need to edit your AFR targets anyway. IDK how much boost you run, but your AFR table only goes up to 150 kPa while your VE table goes up to 230. If you do go up to 230 then you'll definitely want to be richer than 12.7:1.

Your EGO settings are weird. The switch point for an LC-1 is 2.352 volts. Double check based on whatever wideband you have, but 2.509v looks like an uncommon value based on my (admittedly limited) memory. You also have step size set to 15% which is HUGE. With authority set to 10%, that means any EGO correction (when active) will be either +10% or -10% but nowhere in between. That is shitty. Set your step size to 2% and authority to 20% if your VE table is still pretty rough, and change them to 1% and 10% respectively when you are reasonably satisfied with your tune.
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Old 07-27-2009, 05:00 PM   #3
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The whole ego thing is way off in that tune because those settings are from some default tune I found and I have the authority set to 0 anyway. I have a set of settings to go in there once I fix my idle problem. And I am using a JAW wideband, so 14.7 is 2.5v on it.

As for the whole VE table, my car never goes as low as 19 much less 25 at idle. Those rows are there simply for deceleration. My idle is usually about 31-33 kpa.

Here is my car at idle.



EDIT: I just noticed something... in tunerstudio it says my AFR is 13-13.9 at idle, but in the log it says 14.5-15.
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Old 07-27-2009, 05:23 PM   #4
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I'm having the same issues and have just learned to accept my 1100rpm idle. Atleast its consistantly 1100rpms, never hangs below except when its cold. Pretty much been this way since installing my 550s.
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Old 07-27-2009, 05:48 PM   #5
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I am willing to accept the 1100 rpm idle. I just don't like the idle being so rough, with my exhaust I can hear it and it sounds like it missing.
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Old 07-27-2009, 05:53 PM   #6
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Oh, thats a problem I do not have consistantly, but I do sometimes. Usually just for a few seconds on a hot restart it pops and spits and stuff. Also (seemingly dependent on ambient temp) my idle AFR changes which causes some funny stuff.
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Old 08-25-2009, 06:57 PM   #7
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Quote:
Originally Posted by ScottFW View Post
I see from your VE table that you've got some richer values in a 19 kPa row down near idle rpm. If your typical MAP at idle is 19<MAP<24 then it's going to idle really weird because of the different values you have in the 19 kPa row compared to the 24 kPa row. Basically you're leaving MS quite a bit of room to interpolate, so it will fluctuate a lot. I took my typical MAP at idle and have two rows of kPa with identical VEs bracketing that range. So I have cells at 24 and 30 kPa, and 700 and 1200 rpm (four cells encompassing the typical idle range on my car of 26-27 kPa and 800-900 rpm) all with identical VEs. When you adjust the table to be richer or leaner at idle, keep all four of those cells at the same value. You could try that and see if it idles smoother.
After chatting with Savington today, I finally tried ScottFW's idea as explained above. Preliminary results are very positive! With the car warm, I drove for a while and then came to a full stop (as if at a red light, etc.) ... the idle still fluctuated but now it's only between 850-1050, vs. fluctuating quite wildly before from 600 - 1600 .... I also tried this test with the radio on and with the A/C cranked up (for more draw re: stock computer still controls IAC valve) and the results remained positive.

I'm going to keep an eye on this very carefully for the next few days/weeks.
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Old 08-25-2009, 07:19 PM   #8
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I totally forgot about this tread. I have since fixed my problems with my rough idle. My problem ended up being with my timing gears. I have adjusted them and now have better low end power and can idle as low as 700. I had to work to get it back up... I have never had a problem returning to idle, but then again I don't have AC to bog my engine down.
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Old 08-25-2009, 07:32 PM   #9
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Quote:
Originally Posted by DXO View Post
I totally forgot about this tread.
Thanks to the search function, one man's forgotten thread is another's savior!

Or at least it will be if this actually works. All I did this afternoon was conduct a 30-minute test. Long-term is the real test.
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Old 08-25-2009, 09:28 PM   #10
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I'm also going to try changing my VE table so the lowest RPM column is 700 instead of 900, then adjusting the next couple of columns appropriately. Theory: maybe the software isn't making good decisions in the 700-899 range because it's working from zero. (Or does it start the calculations from some higher RPM than zero? Someone please educate me.)
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Old 08-26-2009, 12:23 PM   #11
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I don't think MS extrapolates outside the bounds of the table if that's what you're asking. If your highest rpm row is 6500, then you rev it up to 7500, MS is only going to use the values in the 6500 row. Obviously that's not good. Similarly, if your lowest rpm row is 1200 but you idle at 900, that's not going to be optimal. Your lowest rpm row should be below your idle, and your highest should be higher than you'd ever expect to rev it up, so the engine is always operating within the bounds of the table. Based on the MSQs I've seen posted here, it seems that most guys have their lowest rpm row at 500.
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Old 08-27-2009, 02:12 AM   #12
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Thank you Scott, that is something I didn't know. As of today my RPM columns spanned from 700 to 7000. I'm going to change that high row to reflect my redline.

Last edited by evank; 08-27-2009 at 02:54 AM.
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