Why does my 02 Camaro SS M6 sometimes idles really low?About a month ago I took it to the car wash

the one that sprays high pressure around 360.When I was getting it washed it started shaking and idle was really low.Then my reverse wouldnt go in and my SES light came on,got it scan siad it was front oxygen sensors and the maf was getting low circuit.But I found out it was just my reverse fuse selenoid that was burn so I replaced it and my reverse went in smooth,but it kept burning and I found out that the maf and reverse fuse solenoid use the same fuse.I put new oxygen sensors,new maf and the fuse didnt burn anymore,but the SES light was still on so I took it to advance to get the light erased and it stayed off so that means my car was fine right.But every once in a while I notice my car idle drops to about 600rpm and every time I can smell this different odor from my exhaust not like regular exhaust but like a type of weird burning of something?Anybody have any ideas why it might be doing that?