Haggardfab

Wasn't sure where to post this, if it belongs somewhere else feel free to move it


Little background, I have a 2001 5.3 and 6spd in a 98 Bmw 318ti
Motor has an ls6 cam/springs, Fast 78mm intake and throttle body, ls1 injectors, 1 7/8 headers, Holley fuel rails and an aeromotive regulator running a static fuel pressure of (I believe) 54psi (whatever I was told to run)

I did the entire swap myself and had the ecu re-flashed by LT1swap.com
He basically reflashed my silverado ecu as a 2002 Camaro because of the injectors and cam I have

Now the problem, on decel with the clutch in the car usually doesn't catch itself and will stall or come very close to stalling, I have about 400 miles on the car and sometimes it will do it and sometimes it catches itself at 750-800 perfectly and it's all good but usually it wants to stall

Other then that the car runs great, no misfires, stumbles or hesitation at all, I just cannot figure out this idle issue and it makes the car really annoying to drive

The car isn't throwing any codes and all the info on my scanner is just about what it should be according to the interwebs (except the vacuum, keep reading).. I've replaced the IAC, TPS and MAP sensors and no changes

The IAC counts are between 30-50 at idle, TPS voltage is .78 closed and 4.6 WOT

now here's the one "problem" I found but can't seem to resolve.. I'm borrowing my buddies million dollar snap-on scanner and it's showing the vacuum at idle is 11", on decel from high rpm, in gear, no throttle it's showing the vacuum at 5".. And full throttle its showing 29.9".. It's reading backwards for some reason, it reads the same with two different Map sensors and two different scanners..

I rigged up an autometer gauge to a vac line on the intake and it shows 19" of vacuum at idle, when you rev it up it drops and as the rpm's come down it about 23" until idle where it goes back to 19"

I checked the wiring with the car off, key on and the ground is good and it has a solid 5v at the power.. Signal wire shows very little resistance from the map plug to the ecu plug.. I'm using the factory silverado harness that I modded myself, everything is soldered and heat shrunk and wrapped up

Someone suggested unplugging the map sensor with the car running and see what it shows, the scanner showed 3" of vacuum, I plugged it back in (without turning the car off) and it went to 11" then 22" of vacuum and the rpm's dropped to about 200 and the wanted to stall, I gave it some gas and it went up to the normal 8-900 rpm's and 11" of vacuum

Sorry for the novel I just really wanna figure this out so I can drive the car, I've read probably every thread on the Internet loosely related to this and can't come up with any solutions so hopefully someone has an idea

gagliano7

I know one thing your tps voltage is to high at idle throttle closed. Should be around the .50 range no more than .60. Do a search on how to reset tps. Your IAC counts look good.You might need some tuning on the throttle cracker and throttle follower in you tune.

Haggardfab

I did the reset on the TPS and iac and it didn't help anything, I even swapped in the stock throttle body and that didn't help anything either

I'll play with the TPS/throttle body and see if I can get the voltage down some

Really hoping the car doesn't need the tune adjusted, I just picked up an ls1 that I'm gonna go over and swap in to get a little more power so I don't wanna put money into a tune on the 5.3 that probably won't be in for more then a few months

Haggardfab

Another thing I just thought of, in the process of doing all this I found out the MAP sensor plug had a bad connection and the car would stall if you wiggled the wires.. I spliced in another plug from another harness I have and the car ran perfect for the first test drive of about 5-6 miles (still read 11" vacuum) (it was at full temp before I even left my shop) after I got back and shut it off I went to go for another ride and it was immediately back to the original problem and stalled about 3 times in a row

LS1MCSS

iTrader: (18)

This is in a BMW. Did you hook up the VSS?

Haggardfab

Yes VSS is hooked to the trans and reading according to the scanner.. Bmw runs the speedo off the rear diff so nothing was touched on the GM stuff