Question about 2004 Chevrolet Tahoe

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P0300 - Random / Multiple misfire

I recently changed the plugs and plug wires on my 2003 Tahoe 5.3 V8. I went Autozone and they gave me AC Delco Iridium plugs. They said that these were compatible for my Tahoe and that they were factory gapped at .040. After I changed all my plugs and wires, I fired up my Tahoe. I noticed that I had a slight shudder during idle and it was more pronounced when I put it in gear (reverse or drive) and let the idle carry me forward or backwards. I did not get a check engine light at that point. I reseated the plug wires, but that did not work. I swapped out the Bosch wires for AC Delco wires, but that did not work. I cleaned my throttle body out, but that did not work. I checked for a vacuum leak, but I had none (that I could find with a stethiscope). I added fuel system cleaner, Seafoam, Premium fuel, but that did not work. I recently replaced the fuel filter and fuel pump due to bad fuel clogging the filter and burning up the pump, so I didn' t think that was a problem. Four days later, I finally got a check engine light. I used my autocheck analyzer and found one code 0300 - Random /multiple misfire. I went to a local garage shop and I had them check to see what was misfiring but they could not tell. The check engine light has gone off, but the shudder is still there. I went back to the parts store and purchased AC Delco Rapid fire Platinum plugs that are gapped at .060. I have not installed them yet, but when I pulled out my Chilton book for my Tahoe, it said that the gap for 1999-2003 Tahoes should be .060 and I checked my owner's manual and it said the same thing. So, I might be in a position to fix this problem with the new .060 plugs but I am wondering if it will if the auto parts stores (3 different ones) are right about the Iridium plugs working in my 2003 Tahoe? Could it be anything else?

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  • timoupton Mar 12, 2009

    I changed the plugs to the .060 and I still have the same shudder at idle. I did some more research in my Chilton book and found a couple more possible issues. The Idle control valve and throttle control valve which mounted to the side of the throttle body with rivots. In the book it said that it if it is bad it will cause an erratic idle. When I look at it in my book, it appears to be separate pieces that can be removed from the throttle body but when I look at it on my engine it is mounted with rivots to the throttle body which I assume means I have change out the whole throttle body. Does this make sense or am I headed in the wrong direction? It is just weird that all of this started when I changed the plugs and plug wires.



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Im having this same problem right know, i change the wires and plugs and my car is shaking more than ever. they gave me a gap of 0.40 witch my husband says he thinks its to small. they told me to use the AC DELCO but first were going to try the AUTOLITE 5245 too see if it stops

Posted on Mar 26, 2013

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The .030 may cause a too rapid burn time condition. And Yeah, .060 is standard GM on almost any make/model nowdays.. It may be one of ur coils.. but that would show an individual cylinder.. Try the .060's and let me know.. esp if it wasnt doing it before

Posted on Mar 11, 2009


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