Need some help with diagnosing bad sensors using cable and software - VT LS1 with high idle

[rx22nv]

Hey folks, I have a VT exec with an LS1 and it's suffering from high idling at the moment. The high idle is also causing real hard shifts from park into gear, especially when cold.

I know there are a few causes of High idle, eg vac leak, dirty throttle body, dirty IAC etc. I have an envious customs cable and can read the ecu but my real question is how do I know what is a good or bad reading? Something isn't right but I'm trying to figure out where to start rather than replace every sensor. How do you know what is the normal range? At the moment there are no codes showing but she is idling at 1500, sometimes 1000, sometimes normal at around 800.

I've cleaned the throttle body, cleaned the MAF, new air filter, removed and cleaned the IAC but forgot to dip it in oil when I put it back in. I've sprayed around the intake and the PCV hoses trying to find a leak but now it has to be TPS, Bad IAC, temp sensor or 02 sensors.

Can anyone point me in the right direction?

 

[Fu Manchu]

Wow. You are about to jump in. That’s a good thing. You have some good tools to do it.

I’ll bump something on to you.

Also, start watching some diagnostic videos and Diagnose Dan and early Scanner Danner YouTube videos are the go. Dan is more focused on teaching and showing.

 

[_R_J_K_]

Well, a good start is to make sure whatever the sensors are telling you actually makes sense - i.e. the engine temp isn't showing 25 degrees even though it's completely warmed up, the throttle position matches your foot input, there aren't super contrasting voltage spikes from high to low in individual sensors etc...

Would be hesitant to say it's o2 sensors, they typically just make it drink fuel, don't really have a large effect on idle.

 

[rx22nv]

Wow. You are about to jump in. That’s a good thing. You have some good tools to do it.

I’ll bump something on to you.

Also, start watching some diagnostic videos and Diagnose Dan and early Scanner Danner YouTube videos are the go. Dan is more focused on teaching and showing.

Thanks for that, I will look into the videos as well.

Well, a good start is to make sure whatever the sensors are telling you actually makes sense - i.e. the engine temp isn't showing 25 degrees even though it's completely warmed up, the throttle position matches your foot input, there aren't super contrasting voltage spikes from high to low in individual sensors etc...

Would be hesitant to say it's o2 sensors, they typically just make it drink fuel, don't really have a large effect on idle.

That's where I'll start. The TPS was straightforward and seems to operate normally. 0% resting and it goes up to 80% on full throttle.
I have one 02 sensor that spikes wildly up and down as time progresses. I'll try and get a screen shot of that, it's pretty odd but like you say, I doubt it's the cause of my troubles. It certainly drinks fuel but it's always done that.
I've ruled out the MAF, as it runs the same with it unplugged.
I'll try and play with it some more in the next day or so.

 

[Robdog88]

Hey folks, I have a VT exec with an LS1 and it's suffering from high idling at the moment. The high idle is also causing real hard shifts from park into gear, especially when cold.

I know there are a few causes of High idle, eg vac leak, dirty throttle body, dirty IAC etc. I have an envious customs cable and can read the ecu but my real question is how do I know what is a good or bad reading? Something isn't right but I'm trying to figure out where to start rather than replace every sensor. How do you know what is the normal range? At the moment there are no codes showing but she is idling at 1500, sometimes 1000, sometimes normal at around 800.

I've cleaned the throttle body, cleaned the MAF, new air filter, removed and cleaned the IAC but forgot to dip it in oil when I put it back in. I've sprayed around the intake and the PCV hoses trying to find a leak but now it has to be TPS, Bad IAC, temp sensor or 02 sensors.

Can anyone point me in the right direction?

 

[Robdog88]

Hi. Did you ever get this sorted? I have a VT ls1 with the same symptoms and have done everything you have done also. What was your fix?

 

[lout]

rx22nv has not been on this forum since his post july 2021

 

[rx22nv]

Never got to the bottom of it. I let it warm up and waited until the idle was good, then I unplugged the IAC motor (while running). It needs help warming up but the idling at 2500rpm when stone cold was the worst.

 

[lout]

Never got to the bottom of it. I let it warm up and waited until the idle was good, then I unplugged the IAC motor (while running). It needs help warming up but the idling at 2500rpm when stone cold was the worst.

well how about diagnosing it as you have the tools
first off live data ,
maf reading ,coolant temp and intake air temp

 

[commodoredave]

Hey folks, I have a VT exec with an LS1 and it's suffering from high idling at the moment. The high idle is also causing real hard shifts from park into gear, especially when cold.

I know there are a few causes of High idle, eg vac leak, dirty throttle body, dirty IAC etc. I have an envious customs cable and can read the ecu but my real question is how do I know what is a good or bad reading? Something isn't right but I'm trying to figure out where to start rather than replace every sensor. How do you know what is the normal range? At the moment there are no codes showing but she is idling at 1500, sometimes 1000, sometimes normal at around 800.

I've cleaned the throttle body, cleaned the MAF, new air filter, removed and cleaned the IAC but forgot to dip it in oil when I put it back in. I've sprayed around the intake and the PCV hoses trying to find a leak but now it has to be TPS, Bad IAC, temp sensor or 02 sensors.

Can anyone point me in the right direction?

The IAC and the Ignition coils are often a good place to start diagnosing. If you can, use the envyous software to do a live engine data capture and then post on this site. I have some old engine scans and will see if I can dig them out. In terms of seeing fault codes am not to sure about the accuracy of the envyous product when it comes to reading fault codes. But maybe thats just me.