OKAY I LIED NOT SOLVED!!! Post 11 - Idle surging - 90 SHO

Discussion in 'Gen 1 & 2 - Engine, Exhaust, Drive Line & AC syste' started by boat, Dec 29, 2012.

  1. boat

    boat Likes blue ones

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    On the 90,

    When the car is cold, the RPM's bounce from about 7-800 up to about 15-1800. It is rather annoying, it seems like the car is going to die at times. Now, once it is warmed up, (at least most of the time) it will sit there and just purr like a kitten and not even a blip, stays idling nice and steady.

    I have reset the idle, I have even changed the idle air control sensor, and it still does the same thing.

    It has been suggested to me to swap out the throttle position sensor, of which I have not had time to as of yet. Just wondering if there is anything else that could cause the idle/throttle to surge.

    On the gas mileage,
    I think this could be related, when Timbo had the car and fixed it, he had this code: P172. I filled the tank up, went about 120 miles, and the car got about 10-11 mpg. Now, is this a result of that code, or bad O2's? What does this code even mean?

    Other than these items, the car is a blast to drive, I'd like to get rid of these other issues just so it is more peace-able to drive this daily.
     
    Last edited: Feb 10, 2013
  2. jayro

    jayro Well-Known Member

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    So how much of "Blast" is it to drive? I get about 10mpg when I am having fun with mine.:evilgrin:

    As far as the idle surge....do you have any vacumn leaks? LPM? Clean MAF? I know that there is a differance between the way the ECU manages fuel when it is cold vs hot. Not sure what the code means, but when my O2 sensors were bad my MPG was TERRIBLE!! The sendors have to be pretty bad before any code will appear for them.
     
  3. 93rev2sev

    93rev2sev SHO Member

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    A dried, cold, hard rubber seal will leak until it warms up. Try tightening the intake couples.
     
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  4. rubydist

    rubydist SHO Master Staff Member Super Moderators

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    it sounds like an iac issue to me. I have seen several that work fine cold but not warm, or warm but not cold. when they don't work fine, they are sticky, causing the rpm to surge like you describe.

    I have also put in new ones that were sticky, so just because you have a new one doesn't mean it will work right.

    the leaking intake seal is possible, but normally will cause idle to be high all the time.
     
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  5. boat

    boat Likes blue ones

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    When I move an IAC over that I know was good on another car/motor, it kinda tells me, its not an IAC issue, especially when the symptoms are the same. I may try another known good IAC just to rule it out.

    I will try the coupler thing and see what happens. I'll also try the tb and tps, too.
     
  6. riden2low

    riden2low New Member

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    subscribe
     
  7. boat

    boat Likes blue ones

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    Fixed the idle surging and gas mileage issues.

    For the surging it ended up being the IAC and the TPS. Also replaced the X2J, thinking it had something to add to the mix, probably not tho. :)

    For the gas mileage it ended up not being the O2's, even though it threw a code of P172, it ended up being leaking injector o-ring seals at the fuel rail.
     
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  8. jayro

    jayro Well-Known Member

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    Glad to hear you figured it out and that it wasn't anything too complicated.
     
  9. TimboSHO

    TimboSHO Novice

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    I'm glad I didn't sell you a complete lemon, Mike. I hope you can enjoy it now!
     
  10. Shovert

    Shovert Active Member

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    Fantastic found the problem and thanks for letting the forum know. Now it become a searchable solution to someone having a similiar problem. Maurice
     
  11. boat

    boat Likes blue ones

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    OKAY, I FIBBED, NOT SOLVED!!!!

    This is nothing short of aggravating.

    I can barely pull up to a stop light in neutral without the car dying on me and having to restart the car nearly every time. Other than that, no other weirdness going on, in the way it runs.

    Thought I had this solved when I replaced the TPS sensor, IAC sensor and I still have the same problems, and after swapping the X2J out, with a known good one. So, replacing 3 different things at different times, didn't solve the idle surging.

    I am running out of options. I bought a new TPS from SHO source, put in a known good and new as of this last summer, an IAC I pulled off my 94, where I never had idle surging issues.

    I have ABSOLUTELY NO idea where to go with this. I haven't tried a different maf yet, but this seems to be throttle issue.

    Something else goofy about this whole thing, even after 2 different x2J's, I cannot get a KOEO test to find my CEL codes. No fuel pump kicking on with the fans kicking on, nothing, it just sits there like all you did was turn on the key. It makes me suspect the wiring, (NO OFFENSE Tim), but I have no other idea what is happening here and nothing else to suspect. Not even sure if the 2 issues are related, maybe.

    Its almost like I cannot get a good PCM reset.

    Am I missing something here? Any tid-bits of info would be great here. If I am missing something that you veterans might know of that I missing, please, feel free to share. I would just like to drive this and enjoy it.
     
    Last edited: Feb 10, 2013
  12. rubydist

    rubydist SHO Master Staff Member Super Moderators

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    sounds like you have some wiring or connector issue - may be as simple as a bad connection at the pcm or a nearly broken wire in the loom.

    when you pull off the pcm connector, take a careful look at it to see if any pins are pushed back or otherwise suspect. its not that hard to damage a pin, especially on those connectors that are pulled together with a bolt.
     
  13. vortex2450

    vortex2450 Buying Parts...

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    This may sound redundant of me, but how thoroughly have you checked for vacuum leaks? Even the smallest crack in a PVC hose can adversely affect off load conditions.


    -josh
     
  14. boat

    boat Likes blue ones

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    Right. I'll check it out for pushed back pins. The PCM connector on this car, had a broken bolt, in the X2J, and the other half in the connector. So, a very good chance that might cause this.

    For chasing wires, I'd rather swap the engine harness altogether. I really don't have the patience for that. But, I suppose I would if it really came down to having to fix it differently.

    It would seem like this is poking in the dark trying to find a vacuum leak.

    I think I need to get to a point where I can at least read my engine codes and then go from there. As of now, I can't even do that. It acts like the PCM won't reset, after leaving the negative off the battery for like 3-4 hours. On 2 different X2J's.

     
  15. rubydist

    rubydist SHO Master Staff Member Super Moderators

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    on my red 94, I needed to disconnect the battery overnight for the pcm to reset - I never did figure out why, but a few hours would not reset it consistently.
     
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  16. boat

    boat Likes blue ones

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    Even if you would have swapped PCM's? That does seem odd. :shrug:

     
  17. SHO1

    SHO1 Coke Is It!

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    Unplug the vacuum hose on the manifold that connects between TB/IAC that goes from there down to the evap fuel canister, which is in the lower left front of engine compartment, and see what happens.
     
  18. boat

    boat Likes blue ones

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    Well the issue seems to be that I cannot get a good reset on the PCM and I cannot get a KOEO test to run with 2 different X2J's. I think before I can solve anything, I need to be able to read my codes, can't do that until I can get a good KOEO test. The connector that goes to the PCM, the bolt is broken, so it cannot be bolted to the PCM.

    I am going to try swapping the EEC-IV (engine) harness and see if that fixes it, and maybe, just maybe get a good reset on the PCM and read the codes.

    ONE question: Can I take the same harness from a 93 MTX and swap it in one for one? Is there anything different about that harness from 90-93 MTX?
     
  19. 93rev2sev

    93rev2sev SHO Member

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    Have you swapped intakes?

    Have you performed a cranking compression test?
     
  20. boat

    boat Likes blue ones

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    It is an 80k mile 3.0 that runs like a scalded cat now that I replaced the IAC and the fuel injector o-rings, it runs even better now than when I first got it. When running down the road it runs super buttery smooth, and has excellent throttle response. Once the injector o-rings were replaced and not leaking anymore, my MPG improved as well, by almost double.

    How does a compression test or swapping intakes fix the lack of being able to reset the PCM or being able to get a KOEO test to run, so that I can get my CEL codes? (b/c I am getting at least one I know of)

     

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