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Discussion Starter #1
05 @145,000- Came into the old idle misfire with no code. Performed the normal Throttle Body cleaning like I’ve done in the past for the issue. No avail. Cleaned the MAF as well. Since I am5k from spark plug change, replaced them with the AC Delcos. Feels somewhat more responsive (peppier). But after a bit of driving and idle stops to complete all conditions to prove a fix- misfire reappeared. Same as before, at idle, no codes. Now SOMETIMES at take off a slight stumble. Still, no codes. Anyone else experiencing this and what turned out the fix? I hate to replace all coils or even one if I don’t have something more concrete.
 

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2004 gmc envoy_slt
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Very unusual to have misfire without a code. What does it feel like? And is it only at idle?

A bad motor mount can cause a vibration at idle that might feel like a misfire.
 

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Discussion Starter #3
Engine RPMs change during the events. All plugs were changed today. Afterwards no change in behavior, but an added on highway run, some hesitation which did not experience before. Possibly I have a coil not secure well after plugs changed. But...a brief CEL appeared. Had code read- Multiple Misfire code.
 

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2003 chevy trailblazer_ls_ext
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Check fuel pump pressure just in case

I ran into SOOO many problems with symptoms simialr to this. Replaced pump ($70 Pump) -- Yr later fuel sender went bad. Replaced pump again ($250 Pump) a month later a plug blew out within the pump assembly which, later, required some disassembly to find. The worse part about this was that with the plug blown out, the car had just enough fuel pressure to start (engine would miss a little sometimes and hesitate other times) and run fine cold but once I drove it any distance, it would not restart until the engine cooled. I found that, due to low fuel pressure, the fuel system was vapopr locking when hot. I fixed the plug coming out issue, checked the fuel pressure (55 psi) and all has been good since. Just a thought.
 
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