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  1. #1
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    Default 1994 k1500 350 swap has idle issues

    hi everybody. like the title says i did a 350 swap in my 94. it was originally a 305 but i swapped in a 350. the 350 has a 20 over bore and a comp lw end cam. nothing wild its basically stock. i took the 350 out of a junk truck and completely rebuilt the motor. everything is pretty much new. i even ripped the ecm out of the junk truck which was also a 1994 1500. my issue is the idle. when it starts up it has a really low idle. but it does go up with some time. maybe a minute or 2. im not sure what is wrong since the idle air control valve is new. any advice or help is greatly appreciated. thanks guys

  2. #2
    I'm Awesome Swims350's Avatar
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    other then idle does it run and drive good no missing or anything?


    Chris

    88 K1500 RCSB still under construction.

  3. #3
    War Damn Eagle ChrisAU's Avatar
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    CTS in the manifold IMO. Idle should be higher at crank and for a minute or two until warm, not lower.
    94 GMC ECSB Z-71 (8/14 - Current): 3" BL, 1.5" Crank/Block, 35x12.5 BFG MT KM2's on 15x8 Pro Comp 1069s, Logan's Off Road Bumpers, 10k Winch

    Past GMT400's:
    98 Chevy ECSB Z-71 (7/14 - 8/14)
    92 GMC->Chevy ECSB Z-71 (9/11 - 2/14) *July 2012 TOTM*
    98 Chevy ECSB Z-71 (9/12 - 1/13)
    92 Chevy RCSB Z-71 (3/05 - 5/07)
    93 GMC RCSB Z-71 (11/04 - 1/05)

  4. #4
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    other than idle it does run and drive fine in my opinion. and could you elaborate on the CTS issue

  5. #5
    War Damn Eagle ChrisAU's Avatar
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    Coolant Temperature Sensor. That is the sensor that tells the ECM to command a high idle when the engine is cold to warm it up.
    94 GMC ECSB Z-71 (8/14 - Current): 3" BL, 1.5" Crank/Block, 35x12.5 BFG MT KM2's on 15x8 Pro Comp 1069s, Logan's Off Road Bumpers, 10k Winch

    Past GMT400's:
    98 Chevy ECSB Z-71 (7/14 - 8/14)
    92 GMC->Chevy ECSB Z-71 (9/11 - 2/14) *July 2012 TOTM*
    98 Chevy ECSB Z-71 (9/12 - 1/13)
    92 Chevy RCSB Z-71 (3/05 - 5/07)
    93 GMC RCSB Z-71 (11/04 - 1/05)

  6. #6
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    ok i will replace that as well. just hooked a scanner to it and the computer shows an IAC valve code. which is new so im a bit confused now

  7. #7
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    also even when the truck is warm it idles really low and takes a while to get the idle up. the scanner also showed a MAP sensor code so i replaced that. made some improvement but like i said even when its warm the motor takes a bit to idle and even then it still seems a bit low. i mean ive only put 50 miles on the motor so far. could the ecm not have reset yet? if so about how long does that take? i mean i can drive it its just at startup is when it worries me.

  8. #8
    I'm Awesome Swims350's Avatar
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    you need to let the IAc set itself if that's not been done it should be, you should also clear the computer when you change sensors and such.


    Chris

    88 K1500 RCSB still under construction.

  9. #9
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    ok can you tell me how i reset these things?

  10. #10
    I'm Awesome Swims350's Avatar
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    computer gets reset by pulling the ecm fuse in the fuse box or unhooking the battery.

    the IAC I forget how it gets reset.


    Chris

    88 K1500 RCSB still under construction.

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