P0300 won’t go away!!!

[1997]

Might help you out.
I solved my P0300 issue old school. Scanner i used didn't display specific p0300 codes.

https://www.gmt400.com/threads/rough-idle-p0300-help.49025/

 

[Mech_Lyfe]

1998 Chevrolet 1500
Automatic transmission
5.7L Vortec

I have a P0300 code…

So far I’ve done a NEW:
Distributor, cap, rotor, wires, plugs, crankshaft positioning sensor, mass airflow sensor, EGR valve, fuel filter & battery. I’m pulling my hair out.

On acceleration my check engine light blinks and before the new distributor all of the other new parts I mentioned were installed and it was still idling really rough, it sounded very muffled and choppy. After the distributor it sounds somewhat clearer and I smelt rotten eggs like the cylinders that weren’t firing before started too (?) but it’s still choppy and it has a mean vibration and yes… P0300

Is there something that I’m overlooking? What could it be?!

I was told that I need to time it.
I was told it could be the catalytic converter…
I was told it could be the temperature sending unit…

How do I narrow this down?

First thing that jumps out to me is the “rotten egg smell” followed by the “choppy” sound. Take a temp gun and check the temps of the catalytic converters. Temps should be high, whichever one is colder, I guarantee is bout plugged up or is plugged.

 

[1998OBS]

First thing that jumps out to me is the “rotten egg smell” followed by the “choppy” sound. Take a temp gun and check the temps of the catalytic converters. Temps should be high, whichever one is colder, I guarantee is bout plugged up or is plugged.

That’s exactly what I found out researching today, I’m actually going to do that tomorrow. Thank you!

 

[1998OBS]

Might help you out.
I solved my P0300 issue old school. Scanner i used didn't display specific p0300 codes.

https://www.gmt400.com/threads/rough-idle-p0300-help.49025/

I read through… it ended up being his distributor cap but it happened with my original cap, then after a tuneup where I changed the cap and rotor it was still choppy but honestly it’s gotten slightly better since the full tune up and new distributor but it’s still choppy, not as choppy as before but still not right. I’m thinking it’s the cat…

 

[1998OBS]

I won't take a guess at what your problem is. I can tell you that when I searched PO300 in the search box more than a few guys have had this problem one guy after changing like everything turned out to be his distributer cap which he had already replaced. I am not trying to be mean, I know after 40 years of fixing heavy trucks what it's like to bang your head against the wall. Hope this Helps.

I got a new cap & rotor (same issue), then a new distributor with its own new cap and rotor (same issue, SLIGHTLY noticeable difference towards the better side) but still choppy, something is still up…

 

[1997]

my issue was the original spider, #1 poppet wasn't poppetting ....
my scanner only reported P0300.

 

[Supercharged111]

First thing that jumps out to me is the “rotten egg smell” followed by the “choppy” sound. Take a temp gun and check the temps of the catalytic converters. Temps should be high, whichever one is colder, I guarantee is bout plugged up or is plugged.

I had a truck with a stinky rotten egg exhaust. I drove it, put new plugs in (this fixed the idle misfire), and the stink went away. Rotten eggs means unhappy cat, not necessarily junk cat.

 

[1998OBS]

I had a truck with a stinky rotten egg exhaust. I drove it, put new plugs in (this fixed the idle misfire), and the stink went away. Rotten eggs means unhappy cat, not necessarily junk cat.

Literally everything besides the cat has been replaced, just replaced both coolant sending units today. Where do you even purchase one from in California? Everyone’s like WILL NEVER EVER SHIP TO CALIFORNIA DON’T ASK!!!

 

[Schurkey]

You cannot buy "universal" cats in Communifornia. That's why they won't ship them there.

You have to buy expensive "OEM-style" cats in Communifornia, and perhaps in other states that have adopted CA emissions regulations.

CARB is pickier than EPA.

 

[1998OBS]

Is there any way around that? Does anybody know a guy who knows a guy? Who… knows a guy?