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Thread: 98 350 rough idle

  1. #1
    Junior Member
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    98 350 rough idle

    You guys are in for some fun, I got a 98 chevy k1500 with the 5.7 vortex. I bought this truck rebuilt the engine. And had it down at the dealership twice for the rough idle. I can't seem to fond a vacuum leak ive replaced the erg valve, thottle, iac, all oxygen sensors, but yet I have a small skip at idle. It's got a new distrutor, cap, rotor, plugs and PVC valve. There's almost nothing spare but it seems to still idle rough at stop signs. The only thing I see wrong is that I've seen that the cap isn't horizontal with the block bug it's been timed by the dewlership twice. I'm done Throwing them 85$ an hour when I think I'm a better mechanic. Any advice will help. I do have a slight cam I can send the duration but in my expisrience it shouldnt be.enough to cause this. Thanks guys.

  2. #2
    Senior Member Oldmech's Avatar
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    Wires? you didnt mention them so thought I would ask... Diagnosing this problem is truly going to be a pain. You need to get a scanner on it, and make sure the scanner is held by someone that knows what those readings SHOULD be.. Putting it on a scope would tell you which cyl is doing the skipping, or if it is multiple cyl etc.. sounds like you have done the easy/obvious things already...
    Also, if you took it to the dealer to fix this problem... how are they justifying Charging you if the problem is not fixed?

  3. #3
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    The dealership didn't care, I got a 700$ bill and a "we have no idea" so I'm tackling this myself. I've personally never seen wires cause a problem only at idle. I tried misting them in the dark to see if I could see arcing but they were fine. I'm running out of ideas and have just started thowing parts at it, which as a mechanic I hate to do

  4. #4
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    I've seen wires do this. When the rpms increase, the engine smooths out. The spark is so quick it doesn't totally ground out. It gets enough to the plug so you don't notice it. Anyways, try replacing the wires. They're probably broke down internally anyways. All the other parts except the egr valve you mentioned would make it run poorly, but not misfire. If you're still unsure about if it's a misfire, put a vacuum gauge to it. If the needle twitches, it's a miss. As for the timing, these trucks are not timed like the older ones. The cam and crank sensors have to corilate to plus or minus 4 degrees from 0. The way you check this is with a scanner by observing the cam sensor reading. If the dist isn't perfectly straight across the engine, it's nothing to worry about. If the timing was off, there would be a code 1456 I think. Anyways, try the wires first.

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