I have some questions

[dsmcoder]

I just bought a 1991 automatic gsx and I have some questions. I have a little starting and idling issues. Sometimes it starts right up and idles and sometimes it takes a few cranks to start and it kind of builds up so to speak it starts like at 300rpm then it moves up to 600rpm and stays there for about 2-3 seconds and then idles at 1000-1200, it seams random as it does not matter if it is hot or cold. It idles at about 1200 rpm, I tried the bliss screw and that made it go down about 100-200 rpm, I would like it to be about 750rpm.

I also would like to adjust my boost higher then factory. I have a small 16g turbo and a 3" Apexi downpipe. Could I safely increase my boost without having boost creep or would I have to perform other modifications? Also how much boost would you recommend?

 

[jlkronik]

im not sure about the idle but my friend is running 16 psi on a stock turbo and it does fine, not much of lag at all, and nothing is going wrong
he's had this setup for over half a year now too

 

[cwriley]

for bad idle i would check timing, clean throttle body well, check maf and o2 sensors, and run some seafome through injectors (run it through the vacuum line on the brake booster) and change fuel filter. basic maintenance stuff first.

 

[dsmcoder]

I have already checked the timing and changed the fuel filter. How would I check the 02 sensor and MAF?

 

[eurytopic]

Once warm the ECU will try to keep the RPM's at 750. If it can't, it's often because of a vacuum leak. Do a boost leak test first.

 

[dsmcoder]

I also did a vacuum leak test with a smoke machine and I found no leaks.

 

[eurytopic]

Check the IAC next.

 

[9!'clipseDOHC]

Here is the proper way to set the idle, 1g BISS Adjustment. It is a bit more involved then just turning the screw.

If you follow the instructions exactly and your idle is still high, or random, then your ISC (Idle Speed Controller) is most likely shot. There is an easy way to test it though, YouTube - DSM ISC, pull the ISC off the throttle body (It's just 2, 8 mm bolts) but leave it plugged in to the wiring harness. Have a helper turn the key to the "ON" position while you watch the end of the ISC. It should move in and out. If not, it is bad. Here is a good place to get a brand new one, DSMISC.

Another common issue is that if a dead ISC is left on the car for a long time, it can damage the caps on the ECU. If that is the case, even a brand new ISC won't fix your idle, you will need to get it your ECU repaired first. There is a member on here, Steve, who works on ECU's. You can contact him if this is the case on your car. Also ECMTuning has an ECU repair service, you can contact them as well.

There are other thing you can check too. It is a good idea to get a new BISS screw, o-ring, and cap. Also clean the throttle body very well and replace the gaskets. Make sure it is clean and leak free.

Also your question about the boost, I have a Walbro 255 lph fuel pump and a Buschur/SX AFPR (adjustable fuel pressure regulator) with stock 450 injectors running 91 octane on a 14b. 3" exhaust and solid intake piping. 14 psi is all that I run, after that my AFR's start to climb which means that I am running out of fuel. It varies based on other variables but I would say don't go higher then 14 psi unless you have a logger and/or a wideband o2 sensor.

Hope this helps!

 

[kawgomoo]

Here is the proper way to set the idle, 1g BISS Adjustment. It is a bit more involved then just turning the screw.

Sweet..ive been looking for that. I just bought a 1g auto that idles like crap. On all the writeups i found no one mentioned the diag jumper under the dash!

 

[9!'clipseDOHC]

Sweet..ive been looking for that. I just bought a 1g auto that idles like crap. On all the writeups i found no one mentioned the diag jumper under the dash!

Glad I could help! If you only ground the ignition timing adjustment plug then the ECU goes into ignition timing mode. You have to ground both at the same time to get it into idle adjustment mode.

 

[dsmcoder]

Ok, I tried to check the IAC and I see no movement, am I suppose to try to start the car or just leave the key in the on position?

 

[9!'clipseDOHC]

Ok, I tried to check the IAC and I see no movement, am I suppose to try to start the car or just leave the key in the on position?

You just turn it to the "ON" position. You need 2 people to do it. One turns the key to the "ON" leaves it for a few seconds, the other watches the ISC.

Hope this helps!

 

[cwriley]

check 02 sensor and maf with a voltmeter. both send signals to ecu that adjust fuel to air ratio and if one is not reading properly it will throw the ratio off and mess with rpm's, u can probably read ## repair manual for where to hook up the meter leads

 

[dsmcoder]

ok, i guess it seems my ISC is not working, thanks for your help. Now I would like to talk boost, What boost level could I increase to without having to worry about boost creep because I heard if you have a 3" downpipe you could have boost creep.

I also plugged my car into a snap-on scan tool and my EGR Temperature sensor was reading -12C which is not possible. Could this reading also be caused from the ISC?

 

[9!'clipseDOHC]

ok, i guess it seems my ISC is not working, thanks for your help. Now I would like to talk boost, What boost level could I increase to without having to worry about boost creep because I heard if you have a 3" downpipe you could have boost creep.

You are welcome. I have a full 3" exhaust with zero boost creep at 14 psi on my factory 14b.

 

[dsmcoder]

and you have no other mods, factory everything?

 

[9!'clipseDOHC]

and you have no other mods, factory everything?

Mods are all listed in my profile. As far as fuel mods, I have a 255 lph fuel pump and an AFPR. I have a lot of other mods but the turbo, intercooler, and fuel injecotrs are all stock.

 

[dsmcoder]

I just ordered a ISC and I will update once I get it installed and confirm the fix.

Also I am getting bad gas mileage, about 150 miles to a tank, is this normal

 

[cwriley]

i get 23 but mine is a 2.0 n/t

 

[dsmcoder]

I just got the isc and it fixed my idle, it purrs like a kitten at 750 now

 

[9!'clipseDOHC]

I just got the isc and it fixed my idle, it purrs like a kitten at 750 now