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350 5.7 will not idle

Discussion in 'Chevy Trucks' started by Dondo, Jan 5, 2012.

  1. Dondo

    Dondo Senior Member
    Messages: 158

    I have a 1989 Chevy K5 Blazer with the 5.7 350. The truck runs fine while driving and will idle when the engine is cold. But when the engine is warmed up and I hold the brake at a red light it feels like it is going to stall. If I put the truck in park or neutral the problem goes away and the truck will idle fine. I figured that I needed to do a full tune up. I did the cap, rotor, plugs, wires, pcv valve, and fuel filter. I start the truck back up and I still have the same problem.

    Does anyone have any ideas what the problem could be?

    Thanks for your help!!
     
  2. cwby_ram

    cwby_ram Senior Member
    Messages: 907

    Just a quick thought. Been fighting with this on my truck for awhile. I think mine was the precat o2 sensor. But in all my reading here lately, could it be your brake booster? On my dodge it is vacuum actuated. If yours is similar in operation to mine, could be you've got a vacuum leak somewhere near the brake booster?
     
  3. Dondo

    Dondo Senior Member
    Messages: 158

    I was thinking the O2 sensor as well. I actualy have two new ones in my garage from my last K5 that I never installed before I sold the truck. I will try and find them and put them in tonight to see if the truck will idle. To be honest I'm not sure if the brake booster is vacuum or not. I will look uder the hood when I get home.

    After reading hours of other posts I was thinking that it might be the EGR valve. I'm just not sure if a bad egr will affect the idle and I'm not sure how you test one.

    Thank for your help CWBY!
     
  4. cwby_ram

    cwby_ram Senior Member
    Messages: 907

    No problem, man. Wish I knew more of the older Chevy's. I'm a Dodge guy, but I've been fighting with a very similar issue for a couple months now. I think an EGR could do it, mine doesn't have one. Then again, mine seemed to be the o2 giving the PCM a bad signal, causing it to suck mass amounts of air and stall out. I hope that works for you, good luck! Keep me posted!
     
  5. KingDuramax

    KingDuramax Senior Member
    Messages: 226

    Another cause of this is the distributor. once warmed up when they get some miles on them the shaft binds up. I had two that got so bad that as soon as you let off the throttle they would stall.
     
  6. mrv8outboard

    mrv8outboard Senior Member
    Messages: 197

    Your 5.7 is throttle body injected right? To check the EGR put vacuum to it and the engine should stumble. You can put a vacuum gauge on it to see if it is low vacuum. There is an issue with the distributor shafts in those year Chevy's. The issue was they had stopped the labyrinth groove in the shaft, that led to lack of lubrication on the upper shaft and bushing. This in turn caused vibration that damaged the magnets on the center of the shaft (if this did not happen first the hydrocarbons damaged the magnets as well). The main drivability complaint was stalling in gear stopped or when going from drive to reverse or reverse to drive and stalling. It does sound like your magnet on your distributor shaft is weak. They have gone back to the groove in the shaft. So replace the shaft or the whole distributor.
     
  7. Dondo

    Dondo Senior Member
    Messages: 158

    Yes, the 5.7 is throttle body. I will test the egr tonight and see if this is it. If it's not the egr and I pull the distributor out. Is there a way to see if the distributor is the issue? Or since I will be holding it in my hand any how should I just put a new one back in? I usually don't put a used part back on if I can afford a new one. It's like changing the alternator and putting the old belt back on.

    Thanks for your help everyone. This really has me scratching my head. I thought the plugs, wires, and fuel filter would have fixed it.
     
  8. mrv8outboard

    mrv8outboard Senior Member
    Messages: 197

    One other common failure is the TBI base gasket. With the truck running you can spray some carb cleaner or WD-40 around the bottom of the TBI unit listening for the RPM's to change and a sucking noise if the gasket is bad.
     
  9. jb1390

    jb1390 Senior Member
    Messages: 710

    One other trick you can try is to unplug the 02 sensor, and see if it repeats the problem. When the sensor is unplugged on an OBD1 chevy, it forces into open loop, which will separate computer issues from mechanical issues.

    Does the truck run/shift fine otherwise? Does the torque converter work correctly, with no slipping/binding?
     
  10. Dondo

    Dondo Senior Member
    Messages: 158

    It turned out to be the EGR valve. I had a buddy come over with a vacuum gage and the valve was was bad. Put a new one in and the truck idles perfect again. Thank you everyone for your help!!
     
  11. cwby_ram

    cwby_ram Senior Member
    Messages: 907

    Glad ya got it all squared away! Now if we could get some snow...