Vortec 454 idling problem

[8T7K5]

I posted a while back about issues I was having with my Vortec 454 and the upper intake. Finally got that lined out, put a new gasket on without rtv and it sealed up fine. I also changed the fuel pump and filter and fuel pressure regulator.

Now it's doing something new. When it starts it idles fine at about 7-800 rpm. After idling for 10 minutes or so, it starts idling up and down, from almost dying up to 1000 or so and so on. If I give it a little gas, say up to 1500 rpm, it idles back down to around 1000, sits there for a few seconds, then it's back to the up and down idle. Could this be the tps? I don't want to just start throwing parts at it.

 

[stutaeng]

As usual, I'll ask about any codes. The Vortecs (really, any newer engine) are pretty finicky about the fuel/air ratios. Anything out of range will throw a code. That's a good thing because it gives you a hint.

So did it start doing this after start-up after changing the upper intake? Or did it run fine for some time and then it started doing this? If the former, re-check all of your electrical connections. It is easy for vacuum hoses to forget getting hooked up after assembly.

I'd check for vacuum leaks with a gauge. I bought a $10 HF and helped me narrow down that I didn't have a lean condition, in spite of code saying it was. Turned out to the an O2 misreporting, so it was a "perceived" lean condition.

 

[RawbDidIt]

I posted a while back about issues I was having with my Vortec 454 and the upper intake. Finally got that lined out, put a new gasket on without rtv and it sealed up fine. I also changed the fuel pump and filter and fuel pressure regulator.

Now it's doing something new. When it starts it idles fine at about 7-800 rpm. After idling for 10 minutes or so, it starts idling up and down, from almost dying up to 1000 or so and so on. If I give it a little gas, say up to 1500 rpm, it idles back down to around 1000, sits there for a few seconds, then it's back to the up and down idle. Could this be the tps? I don't want to just start throwing parts at it.

Engine off, key on, unplug TPS run multimeter between ground and variable wire and manually open throttle. Do this slowly, then try it again while tapping the TPS with a screwdriver or light mallet. Voltage should increase smoothly as throttle is opened IIRC.

xc_hide_links_from_guests_guests_error_hide_media

Sent from my SM-G965U using Tapatalk

 

[8T7K5]

As usual, I'll ask about any codes. The Vortecs (really, any newer engine) are pretty finicky about the fuel/air ratios. Anything out of range will throw a code. That's a good thing because it gives you a hint.

So did it start doing this after start-up after changing the upper intake? Or did it run fine for some time and then it started doing this? If the former, re-check all of your electrical connections. It is easy for vacuum hoses to forget getting hooked up after assembly.

I'd check for vacuum leaks with a gauge. I bought a $10 HF and helped me narrow down that I didn't have a lean condition, in spite of code saying it was. Turned out to the an O2 misreporting, so it was a "perceived" lean condition.

It ran rough before I changed the upper intake, but not like this. The main reason I dove into changing the fuel pump etc was because when I gave it gas while driving it, it fell on its face and sputtered. Now that's fixed and this problem showed up. Seems to only do it after it warms up though. The only code it's throwing is about an o2 sensor.

 

[8T7K5]

Engine off, key on, unplug TPS run multimeter between ground and variable wire and manually open throttle. Do this slowly, then try it again while tapping the TPS with a screwdriver or light mallet. Voltage should increase smoothly as throttle is opened IIRC.

xc_hide_links_from_guests_guests_error_hide_media

Sent from my SM-G965U using Tapatalk

Thanks I'm going to give that a try next.

 

[stutaeng]

He's the video that I watched. Simple test to check the mechanical condition of the engine:

xc_hide_links_from_guests_guests_error_hide_media

 

[stutaeng]

He's the video that I watched. Simple test to check the mechanical condition of the engine:

xc_hide_links_from_guests_guests_error_hide_media

 

[RawbDidIt]

He's the video that I watched. Simple test to check the mechanical condition of the engine:

xc_hide_links_from_guests_guests_error_hide_media

This is a good post as well. I posted the instructions for testing your TPS because you asked, but if this started right after replacing your upper intake gasket it's more likely you forgot to plug in any number of sensors, or you have a vacuum leak. Without codes it's more likely a vacuum leak than anything in my experience.

Sent from my SM-G965U using Tapatalk

 

[stutaeng]

Agreed. Unlikely that TPS failed right after the manifold replacement, but you never know. Also, the O2 sensor code might be related to the vacuum leak, because un-metered air is entering the system, without the computer knowing where it is coming from.

Did the O2 code show up after the manifold replacement?

I usually try to do process of elimination before swapping parts. That just wastes money and creates frustration, at least for me.

I made this homemade "smoke machine" a while back trying to prove I had an intake manifold leak, but couldn't find one. Actually worked quite well. However, I didn't find the "smoking gun" I was looking for. Vacuum leaks will manifest themselves as a big puff.

xc_hide_links_from_guests_guests_error_hide_media

 

[RawbDidIt]

Agreed. Unlikely that TPS failed right after the manifold replacement, but you never know. Also, the O2 sensor code might be related to the vacuum leak, because un-metered air is entering the system, without the computer knowing where it is coming from.

Did the O2 code show up after the manifold replacement?

I usually try to do process of elimination before swapping parts. That just wastes money and creates frustration, at least for me.

I made this homemade "smoke machine" a while back trying to prove I had an intake manifold leak, but couldn't find one. Actually worked quite well. However, I didn't find the "smoking gun" I was looking for. Vacuum leaks will manifest themselves as a big puff.

xc_hide_links_from_guests_guests_error_hide_media

Unlikely things do happen, so don't discount it, but I'd put it at the bottom of the list. Although I did just have my oil pressure sender give out right after an oil change, so these things can happen.

Sent from my SM-G965U using Tapatalk