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Thread: RB25 hesitation and weird idle.

          
   
  1. #1
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    RB25 hesitation and weird idle.

    This is one of the weirdest problems I've ever had.
    It seems to mostly do it after a warm start up, but it's random for the most part. There was a period of time (like a week) when it didn't do it at all.
    Basically, the car will idle just fine, until you give it a little throttle (lets say pulling out of the driveway) then the revs drop to like 100 and surge back up to 800ish. If you just let it sit it will surge lower and lower and sometimes die. If you hit throttle hard and rev it to like 3000rpm, it will idle fine for about a minute and then goes back to surging.
    ALSO when it starts doing that, it hesitates at partial throttle. Lets say you're accelerating from 20 to 20mph in 3rd with like 15% throttle. It hesitates and stops pulling, making a slight popping exhaust noise (not loud at all) applying a little more throttle does nothing but spin the turbo faster (i can hear it spool harder and harder with more throttle but the RPM or speed don't change), even builds boost. At like 75%-100% throttle it just breaks loose and pulls hard. Almost feels like launch control but at speed.

    Really annoying when driving around town because sometimes I gotta accelerate at damn near full throttle and people look at me thinking "what an unintelligent man"
    It's been getting worse lately. I don't even know where to start.

  2. #2
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    BTW this is an S14 with an RB25DET (series2) all stock, stock boost. Just exhaust intake and FMIC.
    Swap was done over a year ago, this is a new problem.

  3. #3
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    hey alex ^_^

  4. #4
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    1990 s13 coupe(sold) Red SR s13 hatch(sold) 89' s13 coupe(sold) 92' s13 coupe w/ rb20det (current)
    I had a very similar problem with my rb20det, i had the same mods as you, exhaust and front mount. My problem ended up being a kink in the fuel line somewhere and that caused my fuel pump to slowly go out. i had Svperformance fix the kink in my line and replaced my fuel pump with a wahlboro 255. this fixed my problem instantly, hope this helps!

  5. #5
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    I already have a walbro 255 on mine, and it seems to run very rich.
    I do have a nismo FPR ready to go on so I'll probably throw that on along with a fuel pressure gauge and see if there are any faults in fuel system.
    And hey, Cassie?

  6. #6
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    maf might need to be cleaned??? it could be affecting the sensor...did that to my rb20det when idle was bouncing around a little.

  7. #7
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    I already tried cleaning the maf...

  8. #8
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    check your gap size.
    afr conditions
    check for boost leaks'
    check tps .45 at close throttle and 4.5 volts at wot.
    Check you IAC valve.Some times a sinple cleaning solves it.
    Inspect your coilpacks and look for micro cracks on the lower side of the plastic insulation.

    It's good to install a ground from chassis to motor also.
    But First download the fsm for your motor.R33 ecr33.
    Good thing to have

  9. #9
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    check your gap size.
    afr conditions
    check for boost leaks'
    check tps .45 at close throttle and 4.5 volts at wot.
    Check you IAC valve.Some times a sinple cleaning solves it.
    Inspect your coilpacks and look for micro cracks on the lower side of the plastic insulation.

    It's good to install a ground from chassis to motor also.
    But First download the fsm for your motor.R33 ecr33.
    Good thing to have

  10. #10
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    what BOV do you have? because atmosphere BOV's on RB's make it idle hunt. for example, my BOV opens at 19 vacuum it idles at 17-18 when the revs drop (closer to 100 like you explain) the BOV closes because the vacuum goes to around 10. then it idles up to around 800-1000 and the vacuum can hit -21 and opening the BOV releasing air, confusing the engine with AFR and hence your idle hunt.

    (personal issue of my own sometimes)

  11. #11
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    Koemoto, sparkplugs were changed and regapped. Problem did not go away.
    No boost leaks.
    IAC valve cleaned.
    Coilpacks are aftermaket and new.

    I will check TPS. Something I should have done already to be honest haha.
    How do i check MAF voltages and what am I looking for?
    BOV is a stock valve.

    Yeah I guess I just have to go down this long list of things to check. I just thought it might have been a common problem with these and someone had an easy solution..

  12. #12
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    Also, how do I check my CAS? Do those ever go bad? I swear every time I check my timing it's off. The adjustment seems to last a week or so before being off again.

  13. #13
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    To check the cas you most set the motor to tdc including the camshafts in their marks.
    You remove the cas and listen to the injectors click.By rotating the cas counter clock wise.

    If the cas is gone the car won't start.period.
    The cas controls injectors and coilpacks.

  14. #14
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    Mine had a similar problem and at that time got horible gas miliage. In my case it wound up being too much fuel pressure. I have a Walbro 255 and Nismo regulator and when I dialed back the presure alittle at a time it kept on running better and now it's fine.

  15. #15
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    Have check your fuel pressure yet? While driving. Could be fuel pump control module. Easy way to test is to find the power and ground wire going to your pump in the trunk right by the access plate. Take the ground wire coming from the pump and ground it to anything metal and that will bypass the FPCM and see what happens..

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