94 silverado surges and dies when cold

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by Skandalist, May 13, 2012.

  1. Skandalist

    Skandalist New Member

    I am having a strange issue with my 1994 Chevy Silverado. It has 187,000 miles, with a stock 5.7L 350. For some reason when its idling it “lopes”. It reminds me of a hot rod engine with a big cam. LoL. Anyways, it runs great when your driving it. It has a ton of power and will roast the tires if you want it too. In the past 3 months I have rebuilt the engine because it was burning oil and leaking oil all around the intake, it also leaked antifreeze around the intake. So the block and heads were rebuilt by a local machine shope, with new valve guides, seals, piston rings, bearings, timing set, new cam, etc.. I got the engine back and dropped it back in the truck. After installing all the electrical components, I fired her up and she ran like woman wearing lead boots. So I began troubleshooting and ended up replacing the following parts. Throttle Body rebuild kit from autozone, EGR valve, MAP sensor, Distributor, Cap/rotor, IAC valve, Throttle Position Sensor, Coolant temp, Coolant sender, Knock sensor, Vacuum lines, Ignition Coil, Plugs/wires, O2 sensor

    Sense replacing all these parts, the truck runs great, and has tons of power, but it has this funky loping at idle. Another strange thing is that when the A/C is turned on it idles great. Any help or suggestions would be greatly appreciated on how to get this idle down to normal.

    ---------- Post added at 10:25 PM ---------- Previous post was at 10:23 PM ----------

    Well tonight I cleaned all the grounds.. I got a wire brush and cleaned the connection to the block, and to battery, I also cleaned the connections to the frame and block/firewall. Still has this loping/surging and if I dont give it gas it dies.. After it warms up it will stay running, but still has this loping/surging thing. I am wondering if the computer is acting stupid. It gives me Check Engine light codes for parts that are brand new. Doesnt make sense. I checked the wiring to these new parts and its in perfect condition. Also the BRAKE indicator light on the dash is flashing. Can someone please give me some advice on what to check out next?
  2. ejohnson03

    ejohnson03 Epic Member 5+ Years 1000 Posts

    I actually went through a rebuild similiar to what you have described.

    Setting the timing on this beast is somewhat tricky...

    The key is to disconnect the ECM connection to the distributor, it is the tan wire with a black stripe, located below the glove box, then set your timing.

    With my larger cam and upgraded distributor I set my timing advance to 18 degrees.

    Reconnect the ECM wire and it should purr like a kitten.

    By the way, I also had my ECM upgraded as well.

    If you set your timing properly and still have this issue, could be that the distributor is off by a tooth or two.

    Good luck, let us know how your progress is...
  3. Skandalist

    Skandalist New Member

    Hey, thanks for the info. When my neighbor was over the other night helping me with the timing on the distributor we never messed with a wire behind the globe box. Tomorrow when I get home from work I will do just that. Also, let me get this right... When I disconnect this wire, I gotta start the truck and have the timing light hooked up to piston 1 and point it at the harmonic balancer and set my advance to 18 degrees, then reconnect the wire behind the glove box?
  4. Skandalist

    Skandalist New Member

    Ok, I found a pic on another website. Gonna play with it tomorrow. Will let ya know what happens.

  5. ejohnson03

    ejohnson03 Epic Member 5+ Years 1000 Posts

    yup, that is the one...
  6. dipstick

    dipstick Member 2 Years 100 Posts

    Need to get truck warmed up ..disconnect timing wire...set timing to 0degree .
    If you advance that far 18 degree truck will run bad . Might get by with a few degree advanced.
  7. Skandalist

    Skandalist New Member

    Thanks for the info. I disconnected the wire under the dash, cranked her up and used the timing light to get it to 0 degree. Turned it off and left the battery disconnected for a few minutes, then hooked everything back up and she fired right up. The truck is actually idling much better than before, but still has this "loping".. I checked the manifold and vacuum lines again and everything is hooked up tight. I am uploading a video of what the truck does while driving it. You will see in the video that it drives great, just drags at idle.

    ---------- Post added at 11:04 PM ---------- Previous post was at 10:43 PM ----------

    Also, I pulled the check engine codes and found the following.. Code 32, This code is for the EGR. Code 33, this code is for MAF/MAP sensor. Both the EGR, and MAF/MAP are brand new and have new vacuum lines. And when the intake was off the motor it was thoroughly cleaned. Now for the tricky one, and I think it might be the cause of my issues is a code 42. The following is some info I found on code 42..

    For a Code 42...Electronic Spark Timing Cricuit,
    Trouble Code 42 indicates that there may be a malfunction in the Electronic Spark Timing (EST) system.
    During cranking, the timing is controlled by the ignition module while the ECM monitors the engine speed. When the engine speed exceeds 400 RPM, the ECM sends a BYPASS signal to the ignition module which switches the timing to ECM control. The ECM calculates what the timing should be then "tells" the ignition module via the EST circuit.
    An open or ground in the EST circuit will stall the engine and set a Code 42. The engine can be re-started but it will run on ignition module timing.
    The conditions for setting this code are:

    • System in BYPASS mode but the ignition module is still controlling timing
      - or -
    • Engine speed > 600 RPM with no EST pulses (ECM controlled timing) going to the ignition module for 200 msec.

    Typical causes for this code include:
    1) BYPASS line is open or grounded
    2) EST line is open or grounded
    3) PROM or CALPACK not seated properly in the ECM
    4) Poor connections between ignition module and ECM
    5) Poor routing of EST harness and/or poor quality ignition wires (EMI induced electrical noise)
    6) Faulty or incorrect ignition module
    7) Faulty ECM​

    ---------- Post added at 11:29 PM ---------- Previous post was at 11:04 PM ----------

    Ok, so here is a short video of what the truck does at a complete stop with it shifted in "OD".. When I start driving it, it has lots of power and takes off quite nicely. But when I come to a stop it nearly wants to die. I should have turned on the A/C cause it idles better with the A/C on. I am wondering if the computer is fried on this truck..
    Last edited: May 14, 2012
  8. Pikey

    Pikey Moderator Staff Member 5+ Years ROTM Winner 5000 Posts

    are you reving the motor At about 15 seconds in the video? It sounds like you rev it, but your tac did not move.
  9. Skandalist

    Skandalist New Member

    HAHA, I was wondering if someone would mention that. No it wasnt me reving. It was a guy that lives down the street driving by me while I was stopped in the road. He was driving a silverado also. Much newer though.
  10. Skandalist

    Skandalist New Member

    Well all my friends that I spoke too about my truck say its a vacuum leak. Im letting the engine cool down right now cause my beautiful bride drives it to work. Anyways, I got some throttle body cleaner and once its cooled down I am going to spray it on the vacuum lines/intake/brake booster and see if the engine rev's or dies.. Anyone else got any ideas for this crazy idling problem of mine?

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