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2003 chevy trailblazer_ls
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5 Posts
Discussion Starter #1
Hello all! I’m hoping some of you can help shed some light on my issue… The water pump on my 2003 TB 4.2L 4WD (145k mi.) developed a leak, so we changed it out and at the same time changed the serpentine belt. When we got it back up and running again, it was running slightly rough and would stall when the A/C was turned on. It also threw the P0302 (cylinder #2 misfire) code. We moved the coilpack from #2 to #3 and the code changed to match cylinder 3 so we replaced that coilpack.

I did some searching on the stalling and found many suggestions to clean the throttle body to clear this up. We took the throttle body off and got it completely clean. It doesn’t stall anymore, but the engine is running even rougher and now we are getting a P0300 (random cylinder misfire) code.

We are replacing the throttle gasket today (had to special order it), but I’m wondering if there is anything else we should be checking. Any suggestions you might have are appreciated!
:thx
 

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2003 chevy trailblazer_lt
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21 Posts
when cleaning the throttle body did you disconnect the battery negative or pull the 2 PCM fuses for at least 30 minutes? And then re-connect after being all put back together.
 

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2003 chevy trailblazer_ls
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5 Posts
Discussion Starter #3
We didn't disconnect the battery when we cleaned it yesterday. After doing more reading last night, we saw that we should have so we disconnected it this morning and had it sit for about a half hour. It didn't make a difference in how it runs.

One other thing to note: as far as I know, the throttle body has never been cleaned... (which is why we were leaning toward a bad gasket)
 

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2003 chevy trailblazer_ls
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5 Posts
Discussion Starter #4
OK - the new throttle gasket has been put on. It is still running very rough and throwing the random misfire code.
 

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2003 chevy trailblazer_ls
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5 Posts
Discussion Starter #6
Thanks for the suggestions :D

We're going to take a look at them today and see. They were changed not too long ago, but you never know! This is making me crazy... :crazy:
 

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2004 gmc envoy_sle_xl
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1,239 Posts
Make sure you use only AC Delco 41-103 plugs. Another reason for rough idle is a vacuum leak around the intake manifold.
 

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2003 chevy trailblazer_ls
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5 Posts
Discussion Starter #8
Well...after looking over everything again, it turns out that another coil pack had gone bad. I can't believe we overlooked it :duh:

Thanks for the help guys. :D
 
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