2001 Z-28 6-speed. When Ambient temp is 50 F or less, I have tokeep the under-load RPMsat about 1500-2000 or the engine stumbles (I hope no-one has this happen without bypassing skip-shift). Idle is typically fine though, it only misses under load.

Occasionally (when it's butt-cold out) the engine will idle real rough, and try to die. I rev it for10-20 seconds, turn the car off, and restart it, and its back to only stubling under load.

Once the engine is warmed up a bit, it runs fine. I just popped in new irridium plugs, since it was time anyway. It runs better at low RPMs when its not stumbling, but the hesitation is still there when it's cold.

When it idles bad, the check engine light flashes and stores "multiple-cylinder misfire detected" - which provides zero-help. Other than that, the CEL is not lit, andthere are nocodes in memory.

I'm thinking this is most likely a sensor issue, possibly MAF sensor? It also seems like the O2 sensor might have lost the heating element, but that should throw a code. The gauge temp alway reads correctly, but is there another temp sensor for the OBD-II? Anyone seen an LS1 do anything like thisbeofore?

 

One of the temp sensors, either the IAT or ECT may have drifted, common problem, and need to be replaced. Also if you did the throttle bypass mod, you going to have driveability problems in cold weather. I assume all the regular maintenance stuff is OK, plugs, wires, filters, ETC.. Multiple cylinder misfire is just that, can be caused by poor ignition & poor fuel mixture, or even a clogged cat. The MAF should be OK, otherwiseit would still run bad when warm.

 

Thanks for the info. All the maintenance isup to snuff. In fact, the car runs like a topwhen warm.The only mod I've done is to bypass the CAGS solenoid. That should have zero effect on engine operation. I did buy the car used though. It was a actually a chick car before I got it (found a half dozen different lip-glosses under the driver seat), so you wouldn't expect too many mods.

That being said, I'm actually starting to think the car may have a more agressive cam, and the miss has to do with the computer mappings. My car has out-pulled a few cars it shouldn't have,particularly a few Fbodies that should be equal in all respects.I'm nothing special on a 6-speed, so I have no other explanation. Maybe the previous owners did adda mod or two and whoever programmed the fuel and timing maps did a sloppy job at low temps.

Another thing... When you guys mash the gas in your Fbodies, does the lack of vacuum cause your AC to blow on your feet until you get off the gas? This is another issue I've been scratching my head over. I don't have to floor it, it sets in at about 60-70% throttle.The idle is always smooth, so I don't suspect a vacuum leak.