Hello fellow ls owners, i have a 1990 nissan 240sx with a ls3 in it, motor is all stock except for a tsp stage 1 supercharger cam, 223/231, .629"/.629", 115 lsa, 112 icl and dual valve springs, and a t56 6 speed, im using a ls1 harness, ls1 accessories and ls1 pcm, i had the relucter wheel changed to 24x and did the 3 bold cam swap with the 1x relucter cam gear, car starts up and runs fine, my after market harness might have a flaw and i need an opinion on the situation, the first issue im having is when im coasting to a stop the idle will jump up to ~1600 and hold until im at a complete stop where itll settle at 800 and sometimes 1000rpm, also the speedo will read 10mph when im not moving, i didnt think this was an issue, when i tried to get it tuned they told me it was running too lean, so i wired my fuel pump to a relay and upgraded the fuel line to a 3/8, i went back and after seeing it was getting fuel the tuner said i had ground issues because my aftermarket harness has only 1 engine ground refereed to as the "efi ground" this grounds all the engine electrical sensors/coils/ecm to a bolt on the back of the head, the tuner told me that a stock gm harness has multiple engine grounds that ground the sensors and coils separate from each other and not all bunched up like mine, so what he said was happening is the sensors are picking up the waste discharge which i think is called emi from the coils and that extra voltage is throwing the sensors off making my car untunable, but after doing research on my idle surge issue i came to find out about throttle cracker and throttle follower which need to be adjusted to get rid of the surging, the tuner switched me over to speed density however i get a p0103 maf circuit signal high code, so im kinda at a fork in the road as i dont know how to approach this and would deeply appreciate the input and advice i look forward to hear from you guys

 

It looks like you are quite new here. The ground issue is probably not an issue at all. The high idle is because of the rolling idle tables. Find another tuner. I could be mistaken because there are many variables that can't be 100% eliminated without logs and tune files posted. It does sound like excuses though. If you are going to have a swapped car and expect to do much with it, you should get tuning software even if you will never be a tuner. It's good to be able to scan and dig for problems yourself.

 

I have had problems tuning a car with an ls1 who's grounds weren't connected but it's hard to tell what your issue could be. Like codyvette said if you could scan your car and post the file of the tune we could possibly help you a little more.

 

Your tuner seems like a n00b

 

Yeah, turning off the SES for this when you go to speed density is "Tuning 099" stuff. like before you get to 101. Your hanging idle can be from too much base airflow, throttle blade opened too much at zero, overly aggressive follower or cracker, drilling a giant hole in the blade, a vacuum leak (in SD mode, vacuum leaks hang idle, in maf mode, they cause stumbling), etc. So, yeah, sounds like rookie stuff.

You can use any of several methods to diagnose vacuum leaks. Do that first. if they are all good, you can tune the idle down. That it drops to 800 at a complete dead stop is almost certainly pointing to the cracker being too aggressive and/ or very high base airflow. Can't do much else over the internet without tune files and logs.