2G Idles perfect with MAF unplugged, but idles rough plugged in

[LNS_325]

Hello everyone. I am having a rather peculiar issue with the drive-ability on my 2g. It will idle like complete crap with the maf plugged in, Cold start or at Op-Temp. With the car idling very poorly and hunting for idle around 450-600 rpm. I can unplug the maf and it instantly will rev up smooth out and idle like a brand new car. It is a 95 GST that I got as a roller. I put everything together and got it running but it has had this issue since a day of two after I got it finished up. First off it is a bone stock 99 gst engine with t25 all stock. The only real upgrades are hard IC piping to a 1g side-mount that has a recirculated 1g BOV. 3" turbo back exhaust and a decent fuel system (in tank 255 full -6 an from the sending unit all the way to the Aeromotive regulator). Still on stock injectors. Less those things it is a stock car. I have done lots of trouble shooting thus far and am kind of stuck. Here is the list of things I have done so far. Swapped 3 different maf sensors (the current one on my car is from a car that runs and drives perfectly), swapped three different ecu's one of which was bad and wouldn't star the car at all. The second ecu was a non socketed eprom 95 ecu, the ecu that is currently in the car is a 99 black box ecu. The symptoms are identical with both ecu's. I have done a boost leak test, found a few rotted vacuum lines and a leaky throttle body gasket and replaced those. I just today did a continuity test on all of the circuits from the maf plug to the ecu plugs and what I am assuming to seem ok with about .5-.6 ohms of resistance per circuit. I am not sure on what the resistance readings are supposed to be. I also with the maf plugged in key on engine off did a back probe voltage reading on all of the wires coming out of the maf plug. This is where I am not too sure. I wonder if anyone knows the range of voltages that I am supposed to be seeing at each one of these wires. It would be easier if I had dsmlink to watch a live datalog to see what is really going on. The snap-on scan tool I have had this hooked to communicated so slowly on the live data that it refreshed about every 10 seconds but it didn't really show anything off on what it did read. Long story short if anyone knows what resistances I should be seeing in my curcuits, and what voltage outputs from the maf to the ecu I should be seeing would be greatly appreciated. Or if I am just blatantly missing something obvious I'm always open to other advice as well .

 

[shinzon]

Has the honeycomb been hacked out of he MAF? You can find the procedure for testing the MAF harness in the MFI troubleshooting section. Wiring diagrams can be found there as well:

http://www.dsmtuners.com/threads/download-a-2g-service-manual.324090/#post-151989574

Quickly looking at the wiring diagram:

• pin 1 should have roughly 5v (green with yellow) which is the reference signal for the barometric pressure sensor
  
• pin 2 is grounded by the ECU for the barometric pressure sensor
• pin 3 should have roughly 5v, and is the reference signal for the mass airflow sensor
• pin 4 should have battery voltage and is fed from the MFI relay
• pin 5 should have continuity to ground
• pin 6 should have roughly 5v, and is the reference signal for the air intake temp sensor
• pin 7 is grounded by the ECU

 

[chrysler kid]

Idle smoothing out with maf unplugged is a sign that the map sensors vacuum readings are more accurate than the maf sensors readings of pre turbo vacuum

Make sure you have all of the hoses correctly connected to the intake tube before the turbo and there are no vacuum leaks