Surging Idle and Miss '89 F-Body

Discussion in 'Chevy Truck Forum' started by wirelessrat, Jul 25, 2013.

  1. wirelessrat

    wirelessrat Full Member

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    #1 wirelessrat, Jul 25, 2013
    Last edited: Jul 26, 2013
    I know this is a car, but CC said it would be cool to post up a thread. I hope everyone else doesn't mind.

    I am working on an L98 TPI from an '89 Trans Am. I Ran a compression test on all 8 cylinders and found 120#s across the board with very small deviations on two cylinders of only about 2-3 pounds. I set the base timing by disconnecting EST connector to 6BTDC with car in drive. I then set base idle and finally TPS to .54 volts. When I was setting the timing I noticed that the bulb did not flash on the timing light every single time, but it is one of those cheap timing lights. I am beginning to wonder if something is going on inside the distributor. One thing to note is that when I had the distributor out and would hold it sideways and spin the gear with my hand it appeared that the pickup coil was touching/hitting slightly, but when I would hold it vertical as if it was in the car it would spin smoothly.

    Injectors were all ohm checked and are remanufactured with virtually no miles on them.

    Only getting an intermittent code 33 High Signal MAF.

    Cleaned MAF with MAF cleaner.

    I carefully checked for vacuum leaks with carb/choke cleaner around the intake base, throttle body, runners and plenum and did not notice an idle surge. Also, to further isolate I unhooked all the vacuum lines and plugged them off with bolts just trying to limit the potential for vacuum leaks.

    The CTS is reporting to my computer program (WinALDL) the correct temperature. Unfortunately, I am just not familiar with the various data coming from the ECM to my program to properly interpret the data to help ID a problem. The MAF is showing almost 15grams of air at idle and it is my understanding it should be around 5 at idle. Here is a video for now, but I will replace it tomorrow after I make a new video. Thanks for taking a look and I appreciate your thoughts and ideas. :bow:
     
  2. wirelessrat

    wirelessrat Full Member

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    Here is my spark plug:


    [​IMG]
     
  3. scavanger

    scavanger Full Member

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    Is the engine totally warmed up in the video,,, appears to be running a bit cool , I thought the 89 L 98 had a MAP
     
  4. gpmorgan

    gpmorgan Auto Banned

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    Did the dist shaft have side to side movement. It shouldn't be hitting the pick-up. If it has a vacuum leak, it will make the computer try to compensate which will result in erratic and high idle situations. I recently repaired a leak on a Northstar engine that was doing basicly the same thing. The only thing is that your spark plug looks like it is running very rich but that could be because of the computer over compensating. Just a thought.
     
  5. wirelessrat

    wirelessrat Full Member

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    #5 wirelessrat, Jul 26, 2013
    Last edited: Jul 26, 2013
    During the short video it went from 167f to 180f. 90-92 I believe were the MAP years.


    I did look for lateral play with my eye, but did not observe any. The only way of checking for lateral movement was holding it horizontal and giving it a spin and the pick-up would hit significantly. Then, again, hold it vertical and it was smooth. I am considering a reman job that is complete from top to bottom for around $50,. This is a low mile car with about 87k miles, so I am wondering if I messed something up when I changed the pickup coil out.. That and a set of wires. to eliminate it entirely. I have a new coil already here to put on. I guess I am throwing parts at it now, but I am running out of things I can check.

    I called my machinist yesterday about the prospect of a cracked intake. He told me he can pressure test it, but the odds are very slim that is the issue.

    Thanks for the input guys.
     
  6. scavanger

    scavanger Full Member

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    Have you had the plenum off ? Those runners can warp and make it real hard to get the plenum in without messing up the gaskets . Wouldn't think that 180 should cause your problem but 195 thermostat is what should be in it. Iff it has a rich mixture , check the regulator for gas smell in the vacuum port.
     
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  7. chevychase

    chevychase Semi-Admin
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  8. wirelessrat

    wirelessrat Full Member

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    #8 wirelessrat, Jul 26, 2013
    Last edited: Jul 26, 2013
    Scavanger: When I got the car I pulled out the 160 and put a 195 in it since that was stock. I did sniffthe FPR :woot:for fuel and made sure that fuel pressure changed slightly when I pulled vacuum from the FPR.

    CC the TPS stayed the same because noone was touching the gas pedal.

    At idle this thing is burning gas like a 502 at WOT. I don't think I can afford to start it anymore in this condition. :no:

    Here are some videos I made today:

    Cold Start:
    [video=youtube_share;mgYutTi1UZ0]http://youtu.be/mgYutTi1UZ0[/video]


    After warmed up (not sure I can say if it was in closed loop):
    [video=youtube_share;vADn2h4dB1o]http://youtu.be/vADn2h4dB1o[/video]
     
  9. chevychase

    chevychase Semi-Admin
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    second link not work ..go to second page in google link.. click on back to trouble shooting page A.
     
  10. wirelessrat

    wirelessrat Full Member

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    Thanks for the links and suggestions guys, I will give those links a look tonight.
     

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