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Discussion Starter #1 (Edited)
Any advice would be greatly appreciated.
Backstory - 2004 i5 Z71 Crew Cab. Zero modifications. 100,253 miles as of today. You may recall, I broke the bolts holding the water pump and had to get that fixed. The fix involved removing the front timing cover. After that, the crank seal started leaking, so the front timing cover had to come off again. All of this occurred within a couple of weeks.

So, here's where I am now - The truck is surging, badly. For instance, I can be driving along at 2000 RPM, and all is well - until the tach drops 800 or 1000 RPM and it feels like it's going to stall. Then it'll go back to 'normal'. This will happen several times in a row. It is particularly apparent on the interstate, although it happens around town, too. I do not have any CEL, nor does the scan tool pull a code. So far, I have changed the plugs, cleaned the MAF sensor, replaced the MAP sensor, replaced the air filter, and cleaned the throttle body. I thought my problem was solved as I didn't really experience any surging after doing this. But, late last week, I had to get on the interstate for about 25 miles and the problem resurfaced. And now, it's happening around town again, too.

I briefly had a code that indicated the MAP sensor was bad, but that is clearly not my case.

Any suggestions? I also posted this on the ColoradoFans site, in an effort to get as much input as possible. I need to go out of town later this week, and the trip will be about four hours. However, I'm afraid to drive the truck that far with whatever is going on. Any help would be greatly appreciated!
thanks!
 

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Discussion Starter #3
Merica - Thanks!
This evening, I replaced the fuel filter. Then, I went for a 10 mile cruise down the interstate. The problem is still happening. I do see both dips and increases when I'm running a steady speed. Not sure what the means.

I did disconnect the battery the other night and let it sit for about 12 hours. No changes....

As far as I can tell, the air snorkel connections are fine.

Any other suggestions? Can this in anyway be related to having the timing cover off previously? Nothing was done to the timing itself - just the cover was removed. The problem showed up after that, is why I ask.

Thanks! I also have this question posted at coloradofans, as I have to go out of town this Thursday and I am hoping to get this resolved. :(
 
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