2004 Sierra 1500 - Dead battery replaced, now idle is out of wack

rickf · July 19, 2016

I somehow hit my headlight switch getting out of the truck and the switch was on all day causing my battery to die. The battery was older so I decided to just replace it. After installing the new battery the truck would turn over great a run for a second or two then die out. Before any of this the truck has run great. 130k no issues at all.

I got some info about starting it and letting it run for a bit by keeping my foot on the gas at about 2k rpms. This would would eventually keep the engine from dying and after some regular driving that the idle setting would be relearned and I'd be good to go.

The first part worked...I was able to get the truck to idle high enough to keep from dying and it now idles fine after starting.

My issue is that while driving when I let off the gas the idle goes very low. Sometimes at lower speeds it will die. When I approach a stop light and let off the gas I can feel the engine bog down...It kind of feels like I'm hitting the brakes harder than usual.

Also, in the same stop light situation, if I'm slowing down and the light turns green, when I give it gas it kind of "jumps" back up to a higher rpm for that gear.

Any help is appreciated.

rickf · July 21, 2016

No suggestions?

txab · July 21, 2016

How much have you driven it after the batt. change? Usually it will clear itself after it re-learns. You might try disconnecting batt cables and start over.

SpartanAutoworx · July 21, 2016

Sooo if you have driven it for 20 or so mins and its still not running correctly I would check the TB.

If you hold your foot on the gas around 3k or so for 35 secs you can relearn the crankshaft position sensor. Most of the time this will just throw a light and not effect the way the engine runs. Google the actual procedure but you do not need a scan tool to learn it. Makes it a tad more simple but not required.

I personally would pull the TB and clean it out. If the air bypass hole gets covered it will really act weird esp at idle.

rickf · July 25, 2016

I've driven quite a bit. I'll disconnect the battery and start over. I don't think it's the TB....It ran perfect prior to the battery dying.

Thanks for the suggestions. I'll update after

anumber1 · July 25, 2016

Why would you rule out the throttle body? Other than just saying, "it was fine before", do you really know it "was fine before".

Cleaning the throttle body on these vehicles is more like routine maintenance than a fix. They all need it. The egr system dumps a lot of junk into the intake and I have never seen one that was squeaky clean.

SpartanAutoworx · July 26, 2016

Did you clean the TB yet to see if it would fix this problem?

rickf · July 27, 2016

OK, I'll clean the throttle body....

carkhz316 · July 27, 2016

For sure clean the throttle body. IIRC, there is a bulletin for this issue with the 800's. I experienced this on my '03. I cleaned the throttle body (it was pretty dirty) and disconnected the battery again, just for good measure. After that, it idled perfect again, and didn't have to relearn. What's happening, is the coking of the throttle body is holding the blade open ever so slightly. When the battery is disconnected, the ECM looses that spot it's learned over time, and expects to see the perfectly closed blade as a starting position.

Colossus · July 27, 2016

Ditto on re-cleaning the TB. Also clean the MAF if you haven't done so already (just be real careful when doing this, use residue free electrical contact cleaner) Take the battery cables off, touch them together for a few seconds, and also why not just leave them disconnected about 30 minutes as well, then re-connect, fire her up, do a 30 min drive for relearning (relearning is critical anytime you clean any of the already mentioned sensors) and let's see where that gets us.

Wouldn't be surprised if you have a transmission issue as well but.. let's see how we do with the above first.

Cheers