Stumped with my '98 Camaro, cold idles rough and stalls

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Since I've owned the car, when it is relatively cold out (i.e. under 60F) and the car sits for an extended period of time, it starts up fine then after a second or two starts to idle too low and backfires, sputters, chugs and sometimes stalls. The idle will occasionally rev up to 2-3k then drop back down again and almost stall again. If I hold down the throttle, I can hold it at 2k to manually idle it, but even then it surges a bit even though I'm keeping the pedal perfectly still. I've already replaced the idle air control valve and tried running fuel injector cleaner. It's a 5.7 LS1, automatic, with about 127k on it. It's almost entirely original, but I did have the alternator rebuilt a few years ago and also replaced all of the pulleys/belts/tensioners along with the battery. The previous owner also replaced the EGR valve just before selling it. It does have quite a few CEL codes stored, but I haven't had a chance to get them read since I took it out of winter storage. It runs fine once the car warms up for about 30 seconds to a minute. I'm leaning towards some type of vacuum leak (maybe one of the manifolds?) coolant temperature sensor, or perhaps an o2 sensor is going haywire. I believe these also have some type of air pump to supplement air at cold startup to keep it running rich. I seem to remember a code for this as well when I did have them scanned a year or so ago. Any thoughts or tips would be helpful before I start dumping more money into replacing a bunch of things that may not really be necessary. I'm much more familiar with Hondas/Toyotas and I know on older Hondas for example it was usually either the Fast Idle Thermal Valve or the Idle Air Control Valve, but even then it usually wouldn't act like it would want to stall, the idle would just rev whenever it was in park. Thanks!
 
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Originally Posted by ThirdeYe
It does have quite a few CEL codes stored, but I haven't had a chance to get them read since I took it out of winter storage.
Come on now, you have the best diagnostic leads right there, why aren't you using them?
 
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Clean the mass air flow sensor. Detach the battery neg terminal. Wait five minutes. Reattach the battery. Wait for the cels to reoccur. Then get them read. If you can't clean maf, disconnect it and do the battery disconnect/reconnect. Then start the car see if idle is better. If it is it is the maf.
 
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I'm not a mechanic, just a layman with a 2002 Z-28. I haven't had any problems with that car, but with a Check Engine Light (CEL) and any number of Diagnostic Trouble Codes (DTCs) stored, I would want to troubleshoot each individual code (shop manual or Google) and fix them. You really want your own code reader since they are cheap and a vital tool for diagnosing problems in cars built since '96. Since it has been stored I'd make sure it has fresh gas and a new fuel filter. I'd reset the DTCs (use that code reader we talked about, or by disconnecting the battery), then run it and see which DTCs reappear. Then start the process.
 
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My thoughts are that you should read the codes instead of posting a thread like this first. I keep a tiny Bluetooth code reader in my wifes car and mine along with an app on our smartphones. It saved the day when my wife was far from home in my VW GTI and the HPFP went out. She was able to read/text me the OBD code, described what the car was doing, I got a fuel pump at a dealer, grabbed the needed tools from watching a Youtube video and got the car fixed in 15 minutes in a Speedway gas station. Note: The VW would do a whopping 50 MPH on the low pressure fuel pump in the tank. The cam driven HPFP was very easy to replace. https://www.amazon.com/Veepeak-Blue...ashCommand/dp/B011NSX27A?ref_=ast_sto_dp
 

OVERKILL

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Start with the stored codes. Could be the ECT or ACT sensor, at least that was my experience with similar symptoms on the SBF.
 
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Gotta agree with the others, don't expect any car to run properly with the CEL on, read those codes. Then clear the codes and see which ones reoccur first those are most likely to be related to real problems rather than old incidents that only occurred once. With your OBDII reader, check the live data from the temperature sensors to see if it corresponds with expected temperature. The first thing I would think of here (if there were no codes, but there are) is that the ECT is reading wrong and telling the PCM that the engine is warmed up when it is not. This will cause it to run badly until it actually does warm up.
 
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Originally Posted by skyactiv
My thoughts are that you should read the codes instead of posting a thread like this first. I keep a tiny Bluetooth code reader in my wifes car and mine along with an app on our smartphones. It saved the day when my wife was far from home in my VW GTI and the HPFP went out. She was able to read/text me the OBD code, described what the car was doing, I got a fuel pump at a dealer, grabbed the needed tools from watching a Youtube video and got the car fixed in 15 minutes in a Speedway gas station. Note: The VW would do a whopping 50 MPH on the low pressure fuel pump in the tank. The cam driven HPFP was very easy to replace. https://www.amazon.com/Veepeak-Blue...ashCommand/dp/B011NSX27A?ref_=ast_sto_dp
A friend of mine had this exact same problem on his 2.0L Beetle. Showed a code for fuel pressure and you had to decide which pump was dying. His car would do 65mph but that was it. He ordered the HP pump and we changed it in about 30 minutes. Cleared the coce and he's been back to driving it without issues for a year now. We also pre-emptively changed the PCV assembly soon after that. IT was OE with 120k miles and I told him good insurance and easier than changing a rear main seal which had a good chance of failing if the PCV failed. Gotta love VW's.
 

ThirdeYe

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I had the codes scanned last year, but cleared them to see what would come back. However, with the Coronavirus going on, I haven't been driving it nor have I wanted to take it to get it scanned. I do not have an OBD scanner. I was literally going to have my friend at work scan the codes for me the day they closed our building and enacted our statewide lockdown. LOL Just thought I'd post this to see if anyone else had the same issue before. I disconnected the battery during winter storage and the codes did indeed comeback, I'm just not sure which ones yet. I had some similar issues with my old Firebird where it would stall out immediately after starting it and when coming to a stop while driving. It turned out to be the mass air flow sensor in that car. I'll look at getting the codes scanned once this passes. I also think it has something to do with whatever in this car controls the loops, MAF, or possibly a vacuum leak. I'm not a mechanic or very mechanically inclined aside from basic, routine maintenance. Thanks for all of the input. If I think of it, I'll post back once I get those codes re-scanned.
 
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