i recently purchased a 98 neon sohc 4 door for a couple hundred bucks with a few new parts good deal right.......wrong....car would start but then stall within a minute or so....my first thought was fuel pump....so in spite of trying to buy and resell this thing and make a couple dollars on it...i headed to the local junkyard and picked up a used fuel pump....threw it in started up drove it to the store ran great........next day i went to get in a start it crank crank crank nothing.....sputter sputter. it wouldnt stay running...so i pulled the line from the rail put it in a bottle it primed just fine...put the line back on the rail....cranked it and it started up....great right it works...so i throw it in reverse go to back out and it stalls on me...start it back up and give it a little gas and the engine like falls flat on its face sounds like it dies so i immediatly let off the throttle and it stays runnin...so i let it warm up a bit give it a little gas and it works drives runs fine nothin wrong....little sluggish but whatever...it has a rpm drop when im at stop signs or lights but always comes back up...so i was playing under the hood and see the vacuum that goes to the throttle body, i pulled it off while it was running and it seemed to idle BETTER....strange....so my question is whats that vacuum for....and why does the engine fall on its face when its cold like that any ideas would be greatly appreciated thanks

 

The vac line is for the evap system...

neons are sorta known for doing that when its cold at least ones in the 120k range...

do you have a cel light on???

 

yes i had the codes scanned and i got faulty coolant temp circuit, random misfire, and cylinder 4 misfire, im really only concerned about it trying to stall on me when i first start it. if it happens alot in the higher mileage neons how do i fix it

 

well i think you just answered your own question... your running on 3 cylinders... that missfire is a serious serious problem...

 

that still doesnt tell me why it will not start when its cold....then once it gets running run fine

 

Yea okay listen misfire. It wont start right because of you only running on 3 cylinders. Maybe when it warms up it works it out. I would compression check, injector check, coil pack check, sparkplugs/wire check, and maybe clean the egr while ur at it.

 

problem solved coolant temp sensor fixed the hard starting problem and rough idle