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Thread: rough idle issues

  1. #1

    rough idle issues

    so ive been noticing some really rough idle lately, and i looked overat my boost guage during this and it was fluxuating like crazy. I have tried 2 different cam tables on it and am currently running the tables nick posted(thanks nick). I however dont think that its the cam tables because it did it with both sets. I was also told maybe a boostleak?
    Heres a video of it, its kinda hard to see, but you can see the needle moving up and down.
    http://s178.photobucket.com/albums/w...t=8b60bc74.mp4

  2. #2
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    Uh oh. Better break out the compression gauge. Does it sound like a Subaru?

  3. #3
    it doesnt sound bad, and it just does it randomly. One time i could be sitting at the light and nothing, next light it will start doing this.

  4. #4
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    Hmmm. If it's intermittent you might be ok. When it's doing it go back to the exhaust and listen to it there. Put your hand over the pipe and see if the flow is even or pulsing. If you have a compression gauge it would be the first quick and easy test I'd want to do just to rule out a broken piston or valve issues.

  5. #5
    i would hope not, i have a brand new block lol. Im gonna throw the stock file on and see if its doing it tomorrow. How much are the compression guages and how do you use them, sorry for my noobish-ness.

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    Oh, I figured you were stock, that's why I was thinking pistons. If they're forged you should be fine.

    You can pick up a compression tester pretty cheap from your local parts store or tool store. You don't have to spend a ton on one, you'll be looking for differences between cylinders more than the actual number. Doing the test is pretty easy, just pull all the plugs, put the gauge in the first hole and crank it over 4/5 times. (meaning 4 or 5 times that the compression gauge needle rises from the cylinder's compression stroke, like 4 or 5 seconds of cranking.) Repeat 3 more times and look at the differences in pressures. You'll know if it's good or bad, less than 10% dif is good. If it's bad it's usually really bad.

  7. #7
    ok thanks for all the info. However i threw the stock file on this morning and this diddnt happen. I might just switch to the stock cam and see if that fixes it. Ill probably still go pick up a tester for the future though. I also read you should pull all the plugs and fuel pump fuse, should i?

  8. #8
    Advanced Tuner BackyardTurbo_FTW's Avatar
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    Im going to post my new final tables from the E Blend stuff in that thread, I dropped the idle area timing back a bit and the idle became quite a bit smoother. Keep an eye on that thread, Ill have them up soon!

  9. #9
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    Yeah for those that don't know, idle smoothness and control is a balancing act between ign timing, fuel mixture and airflow. Cam timing isn't, or at least should not be a factor at idle. The cams will/should be parked on cold starts and at idle.

    Here's the balancing act... Too much airflow and the ECM will try to control idle speed by retarding ign timing. Too little airflow and it will advance the ign timing too far. Too much ign timing and the throttle will be too far closed, loosing the control it needs. Too little ign timing and you'll have the throttle too far open to maintain an idle speed, again putting the throttle plate range on the end of it's control. (it only has a certain amount of control for idle speed, it's not like it can go full throttle trying to maintain an idle!) I've found on the LNF's that 15-20 degrees ign timing is the sweet spot for smooth idle and good airflow control. 15-20 degrees on cold start will give the motor enough power at idle to maintain a smooth control of rpm without excessive airflow. (Cat warmup off of course) More ign timing than that and it will start to hunt or surge, same with too little.

    The reason this is hard on the LNF ECM's is the fact we can't see all the idle tables. There are tons of tables that control idle. Basically those tables tell the ECM what to use and how much to use of ign timing or airflow to control idle speed. You don't want to take away either of those ways of controlling idle speed, you want to make sure they are both in the centers of their control range, and aren't fighting each other trying to control idle speed. Most would think it's all about how far open the throttle is, but ign timing is a huge factor in idle control. Ign timing is WAY faster than moving a throttle plate, that's why it's used to smooth idle speeds. If you have a nice, smooth ign timing graph at idle, that means the airflow is so close that it's maintaining a smooth idle without much ign timing intervention. If the ign timing is up and down all the time, that means it's trying to maintain that idle by varying timing. If those swings are excessive, that's telling you it's having a hard time controlling idle rpm's because something else isn't right or it's fighting it.

    Make sense?

    I know I didn't even mention idle fuel mixture, that's another subject!

  10. #10
    Advanced Tuner BackyardTurbo_FTW's Avatar
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    Very true, and good info as usual.

    If you watch the timing at idle, you will see it fluctuate to control the idle speed. You can also see what John is saying about the cams being parked at 0 while idling.

  11. #11
    Advanced Tuner silverbullet08's Avatar
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    I get a wierd idle problem like this randomly. It just started it today after going back to my E tune. I checked all my tables In the idle areas and they are the exact same as my gas tune, only thing that is different is the injector constant. it will idel completely smooth for about a minute or longer with a smooth ignition timing graph "0*-4*" the entire time then it will make a random spike to 10* and drop back to normal for a few seconds then spike again. It causes the STFTs to make a steady long sway going positive then negative by about 3-4% both ways... Like i said though I run this tune all the time and it just does it randomly out of nowhere
    HP-Unlimited Tuning and Custom Fabrication
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    1989 Chevy single cab 5.3 swap "Turbo to come"
    2012 Chevy Cruize bone stock mid 14s on 93octane and tune

  12. #12
    Advanced Tuner BackyardTurbo_FTW's Avatar
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    Possible air leak? have you ever changed the front O2 sensor?

  13. #13
    thanks nick, and thanks for the good info gmtech!

  14. #14
    Advanced Tuner silverbullet08's Avatar
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    Quote Originally Posted by BackyardTurbo_FTW View Post
    Possible air leak? have you ever changed the front O2 sensor?
    Yea changed it about 5k miles ago. Done many boost leak tests and had a few but they are all good now... so idk
    HP-Unlimited Tuning and Custom Fabrication
    Houston area performance parts dealer
    2007 first ever LNF swapped cobalt.
    1989 Chevy single cab 5.3 swap "Turbo to come"
    2012 Chevy Cruize bone stock mid 14s on 93octane and tune

  15. #15
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    Scroll to the bottom and see which one of the settings you gauge is doing, it should help diagnose. http://www.secondchancegarage.com/public/186.cfm
    1994 Mazda Miata turbo, aero, hoosiers Class=SSM

    Take my drop box referral and we both get an extra 250 Mb free!

  16. #16
    great link! it looks like #11 which means retarded engine timeing, might change up my idle timing and see if that gets rid of it.

  17. #17
    Advanced Tuner silverbullet08's Avatar
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    Whats wierd about my issue is it does it a few seconds after you stop then it starts to go away slightly. If you turn the AC on then it goes away completely. STFTs sit at .8 to 0 the entire time. I worked on the idle timing slightly just making sure those areas were close "which they were showing a 4*difference between 15,20, and 30%load areas. I pulled those closer together and raised it slightly. this helped alot but still isnt completely gone. Another wierd thing is that on my histo for STFT and LTFT they show like a 1-3% varience all over which is typical but the idle cells show 17 to 23! ? I tried multiplying those in to see what happened and it made it worse so i went back and used a small percentage. this helped as well
    HP-Unlimited Tuning and Custom Fabrication
    Houston area performance parts dealer
    2007 first ever LNF swapped cobalt.
    1989 Chevy single cab 5.3 swap "Turbo to come"
    2012 Chevy Cruize bone stock mid 14s on 93octane and tune

  18. #18
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    Post up some logs or at least screen shots of logs so we can see what you guys are talking about. If you post a whole log, start recording before starting the engine so we can see warm and cold startup also.

  19. #19
    will do tomorrow if i can plow my way out of my garage, i feel like im living on an island... 4 days of rain!

  20. #20
    messed with the idle timing and no more rough idle!