00' Sierra 1500 Not Idling Correctly

ddresser13 · May 13, 2010

New member!

Anyway, I bought a 00' 1500 Sierra (128k). It ran great for a week then the check engine light came on and when I ran the code it showed as a o2 upstream sensor. So I have been driving it for a week with that light on while the o2 are being shipped in. (they'll be here tomorrow).

Here's the deal tho. Since that light came on the truck has a hard time idling. It goes up,down,up, down,up, down between 1000rpm - 400rpm. but does not die. and contiunes that all day. It also dims the dash lights and I can see the battery gauge fall under 14v's. (New battery was put in last Thursday)

I need some help. Will the o2 change out help? or what else can I look at. Thanks for looking at this for me!

Nytemare · May 13, 2010

New member!
Anyway, I bought a 00' 1500 Sierra (128k). It ran great for a week then the check engine light came on and when I ran the code it showed as a o2 upstream sensor. So I have been driving it for a week with that light on while the o2 are being shipped in. (they'll be here tomorrow).

Here's the deal tho. Since that light came on the truck has a hard time idling. It goes up,down,up, down,up, down between 1000rpm - 400rpm. but does not die. and contiunes that all day. It also dims the dash lights and I can see the battery gauge fall under 14v's. (New battery was put in last Thursday)

I need some help. Will the o2 change out help? or what else can I look at. Thanks for looking at this for me!

Yeah, it has no idea what the Air fuel mixture is, so it keeps correcting it, screwing with the idle. If you replace the O2 sensors and still have a problem than it's something else...keep us updated

Welcome to the board

rmck490 · May 13, 2010

What was the code? That may help others to help you better.

Since the idle surge started with the CIL coming on for the 02 sensor, it could be the problem. Or, maybe not. The PCM could be adjusting the injectors fuel flow based on bad data coming from the sensors thus possibly adding and subtracting fuel incorrectly and causing the surge at idle. Your dash lights dimming could be from the fluctuating altenator current due to this idle surge.

Install the new 02s and see if the problem goes away first. It might also be related to the Idle Air Controller on the throttle body but wait and see what happens with the new sensors. It wouldn't hurt to take out the IAC and clean it either.

ddresser13 · May 13, 2010

What was the code? That may help others to help you better.

Since the idle surge started with the CIL coming on for the 02 sensor, it could be the problem. Or, maybe not. The PCM could be adjusting the injectors fuel flow based on bad data coming from the sensors thus possibly adding and subtracting fuel incorrectly and causing the surge at idle. Your dash lights dimming could be from the fluctuating altenator current due to this idle surge.

Install the new 02s and see if the problem goes away first. It might also be related to the Idle Air Controller on the throttle body but wait and see what happens with the new sensors. It wouldn't hurt to take out the IAC and clean it either.

Thanks for the help! I'll re-run the codes tonight and repost after my ball game. I hope it works

ddresser13 · May 14, 2010

I didn't get a chance to run the codes last night but funny thing....The CIL did not come on at all after work and the truck ran great and normal. So, I'm still going to change out the o2's so there is no more problems. I'll check the codes when the CIL comes on again.

Nytemare · May 14, 2010

I didn't get a chance to run the codes last night but funny thing....The CIL did not come on at all after work and the truck ran great and normal. So, I'm still going to change out the o2's so there is no more problems. I'll check the codes when the CIL comes on again.

Odd...

I would clean the Intake, TB, MAF and fuel system...you may have carbon build up that is confusing the sensors.

ddresser13 · May 17, 2010

Changed out all four sensors, reset the CIL, truck ran great and no CIL. Then, hour later when I'm headed to church, the CIL came back on. So, I'll check the codes again this afternoon and post the codes.

ddresser13 · May 18, 2010

Morning!

I ran the codes yesterday and found it saying "Downstream Sensor No Connectivity" so, I guess I'll be grabbing some electrical gel to possible fix this. Those sensors are brand new! Any thoughts?

I forgot the codes again sorry.

Nytemare · May 18, 2010

Morning!
I ran the codes yesterday and found it saying "Downstream Sensor No Connectivity" so, I guess I'll be grabbing some electrical gel to possible fix this. Those sensors are brand new! Any thoughts?

I forgot the codes again sorry.

Yeah...probably just not making contact...the plug on the truck may be a little corroded..some contact cleaner and dielectric grease should fix that up.