For awhile now my car's had this weird problem where if I punch it in first gear till about 3-5k and suddenly push in the clutch (I know it's not the best thing to do), sometimes the revs will just float around there for several seconds, quite often even rising 1-2k rpms. It'll come back down eventually, and if I release the clutch pedal it'll come right back down, it doesn't try to accelerate like a stuck pedal or nothing. It doens't happen all the time but it does bother me.

Now yesterday I go somewhere and park. Everythings fine. As I come out a LT1 T/a comes up and I talk to the guy. He wants to hear the cutout so I start it p and rev it up to 3k. I shut it off right after. I go to start my car to leave 5 minutes later and the damn thing wouldn't hold an idle. It kept dying if I didn't give it gas. I drove it around for awhile and it finally started to idle at 500-600. After another 20 minutes it came back to normal. Besides the surging I've never had a problem so I don't think it's a vacuumn leak. It always hold a steady 800 idle. I did bring it to a deal for my cats and I was told he pulled a code for a bad MAP sensor, but I tested it twice before going in and never got that code, plus I don't have any now, even when it wouldn't idle. Any ideas? Thanks.

 

Most of what you describe is normal. Drive it normal it'll act normal. Do oddball stuff and the computer can get confused as to what's going on.
When you bring it up to 3-5000 rpm in first gear and push in the clutch the comp expects that you're going to shift to second and it'll keep the revs up for a smoother transition.

 

i always thought that what you were describing was just the inertia of the engine/flywheel. but yeah i could understand that i guess. however, my car does it for several seconds, sometimes around 4-6 sec. of floating. also, what about the fact that it woudnt hold idle? i did a search here regarding the map sensor but couldnt find any pertinent info. what does it control, and what are the symptoms of a bad sensor?

 

I am pretty sure the LS1 doesnt have a MAP sensor, only LT1. LS1 has the MAF sensor. Pretty sure but could be wrong

 

i think map sensors are common to most, if not all, new cars. the maf registers the air coming right past the filter while the map senses it past the TB and in the actual intake manifold. i think its like a check-recheck thing.