Rough Idle
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Rough Idle 
From the top; here's what happened. I have an 02 T/A with a stroked LS2, heads, cam,the works. Ran it during the winter without a thermostat and notices a lot of oil consumption and performance loss. I installed a thermostat and it still burned a lot of oil and hesitated a lot at WOT, then one day it started having problems starting, like it was missing for a few seconds then would fire up. It got progressively worse and eventually started backfiring and wanting to stall and the idle would climb to 2K then drop to 500with backfiring every few seconds. It was also throwing the insufficient switching code. I parked it for a while until a guy I met hooked his laptop to it and noticed the right bank was running way rich but the left was fine. then we checked the plugs, they were seriously blackened. Changed the plugs and O2 sensors and the SES went away but it stills idles a bit rough, then the idle raises to 1300 rpms then the car backfires and the idle drops to 500 rpm and below. then raises,, bakfires and drops again and so on. Any ideas on how to fix this? Get a tune in the time of year you will be using the car. From a qualified shop that has LSX tuning exp. Also make sure your car is running mechanically fine. So new wires/plugs/filters/fluids so on and so forth.
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Teching In
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Okay. I did swap the plugs with NGK 4177, fluids have been replaced and have MSD wires. I drove it to work this morning and at first the clutch was making so much noise, I couldn't tell anything else. The clutch calmed down and the car drove and ran smoother the longer I drove it. while in neutral it would rev up to around 2K then slowly fall back down to around 900 rpm. then a few backfires.. Do you think the computer is trying to re-time itself or something like that and causing the idle and backfire?
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Yeah, in the beginning, I had it dyno and tuned. Later on this guy out in Arizona NickD tuned it for taller tires. At the time the IAC was shot and he tuned the car to basically not stall. I think he adjusted the idle and cracker. Then I replaced the IAC a few months later.
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Go get it redone. Basically as long as there are no leaks, the PCM is need re-adjustment. You could unhook the battery and see if it goes back to "re-learn" and may get better for a short time.
Long story made short, retune.
Long story made short, retune.
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Teching In
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Okay just fired it up and it never idled above 1K but ran very rough. like it's missing but I changed the plugs yesterday. It really sounds like half the engine is working. As it warmed up the idle started to slowly get steady, then backfire and the idle drops and stumbles for about 10-15 sec, then the cycle starts over again.
