Problems Again..
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Problems Again.. Went and had my 1999 SS tuned a few days ago and it has run fine until today. The first thing happened was the check engine light came back on, and now I am getting a idle issue with a raw fuel smell with smoke at the back of the car. I do know the valve seals need replacing, but what I am smelling is fuel. The mods are slp lid, kooks Lt's, 3" exaust, and camshaft. It had these same issues before the tune, and it seems they are coming back... What could all this mean? Thanks..
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Today I scaned, and it is showing a po121, throttle pedel position- Also it is showing a po155 for the bank 2 O2, and a po327 knock sensor bank1 circuit low. I replaced the O2 and seemed to help a little. Has anyone else had these issues?
Had the same issues with 2000 LM7 (5.3 LS motor). Replaced knock sensors to stop getting codes for that but that shouldn't affect idle. If you get or expect knock at idle you've got more serious issues. 
Throttle position sensor(TPS) on the side of the throttle body likely will need changing as well and that is likely your idle problem. This is how the computer would know if the throttle is open(and how far open) or closed. Sometimes this can be a fluke and you can try clearing all the codes, restarting the engine, and see if it idles. If not, then I say replace the TPS. While you are at it, get some electronics or MAF cleaner and clean the inside of the mass airflow meter(MAF). The little wire-looking bits in the middle are the most important to clean. You'll have the intake piping off so some throttle body cleaner wouldn't be a bad idea if you haven't cleaned your TB in a while.
If this is a high mileage vehicle you may be headed for a new IAC(idle air control) valve as well. This is also on the TB and what determines airflow to the motor in order to keep it idling. Sometimes you can take it out and clean the crap built up in the hole there.
I changed all of the above and got perfect idle. Again, the knock sensor has nothing to do with idle, but it will affect power production when accelerating under load.
The IAC is stupid expensive..like $100-ish at the parts stores FYI. I found one on eBay a while back and it actually worked!
Throttle position sensor(TPS) on the side of the throttle body likely will need changing as well and that is likely your idle problem. This is how the computer would know if the throttle is open(and how far open) or closed. Sometimes this can be a fluke and you can try clearing all the codes, restarting the engine, and see if it idles. If not, then I say replace the TPS. While you are at it, get some electronics or MAF cleaner and clean the inside of the mass airflow meter(MAF). The little wire-looking bits in the middle are the most important to clean. You'll have the intake piping off so some throttle body cleaner wouldn't be a bad idea if you haven't cleaned your TB in a while.
If this is a high mileage vehicle you may be headed for a new IAC(idle air control) valve as well. This is also on the TB and what determines airflow to the motor in order to keep it idling. Sometimes you can take it out and clean the crap built up in the hole there.
I changed all of the above and got perfect idle. Again, the knock sensor has nothing to do with idle, but it will affect power production when accelerating under load.
The IAC is stupid expensive..like $100-ish at the parts stores FYI. I found one on eBay a while back and it actually worked!
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Thanks for the info, I did clean the MAF with some rubbing alchol and some Q-tips. I have not changed the TPS or the IAC yet. What do these 2 cost? I have good power under full throttle.. Thanks
TPS should be about $30-$40. Expect knock sensors to be about $50/ea. On earlier LS1s you have to remove the intake manifold to change it so change both while you are in there. There is also a new knock sensor harness that the parts stores sell for around $30 that I recommend you get if/when you change these. Generally after a lot of years you will do some damage to said old harness when removing and the grommets/rubber seals will likely be dry-rotted.
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Thanks for the info again, I will buy those next. I have just bought this car last month and im trying to get it up to par. I have noticed the idle is better with the new O2 sensor but it still has a strong possibly a lean fuel smell at the back. I called the tuner and will take it back to him soon to check it out.
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Verdad Gallardo Np. BTW, you may have rich/lean backwards. If you are smelling fuel, that would be referred to a "rich" situation. "Lean" would be too much oxygen compared to the amount of fuel..not enough fuel therefore lean. Then again maybe you have a more keen nose than I and can smell a lean condition at idle. I can't.