Only idles with MAS unplugged, help!

[xhaust50]

I have a 90GSX with a Big 16G, 255lph, 550 Injectors and a 2g MAS. The car has been sitting for a few months, but I didn't like the way the car ran before that so I bought a new chip for it from Jeff at Keydiver. With the chip installed, the car will run perfectly for a few seconds and then die. If I hold the RPM's up it will stay running and sounds fine, but dies at idle. The car idles fine with the MAS unplugged.

There are no vacuum leaks, and according to my logger everything seems fine with the MAS. I contacted Jeff to see if anything seemed wrong in my chip portfolio, but he couldn't find anything. Right now I don't have an SAFC or an AFPR because I planned on getting a basic tune with the chip first and fine tuning afterward, but I should have an SAFC by Wednesday.

I was wondering if I can check anything else in the meantime. At idle, the FP is at 43psi with everything connected. I guess this is a little high, but I wouldn't think it's high enough to keep the car from idling. There is also no smoke or anything out the tailpipes. The fuel may be about a year old, I'm wondering if that is the problem or at least part of it. I'm getting an AFPR for xmas.

Any ideas?

 

[pitbull419]

Safc and afpr should fix your problem.

 

[xhaust50]

I hope so, but I have the same setup in my car now and even if I set the SAFC to 0 it still idles. I don't have an AFPR either, but I don't have a gauge on it so maybe the FP is closer. Could it be anything else?

 

[turboglenn]

It sounds like a bad idle control motor, or a bad Mass air to me. Do ou have a spare ECU or MAF sensor you could use to try for a few minutes? Or swap IAC's with some for a few minutes as well.

 

[ROOKIE1]

I've always read a 255 without an fpr is a no no . Check your wiring on your mas . Try a different one .

 

[xhaust50]

Well I checked the MAS readings on a logger and all of the numbers seemed okay (airflow, temperature, etc.). I'll try swapping the MAS's between my two cars. I can't swap my ECU's because one is an Eprom and one is not.

 

[jlado13]

You cannot run anything above a 190lph with your stock FPR. The pump will overrun the stock FPR and you'll just be dumping fuel into your combustion chamber. So, like pitbull419 said, SAFC and AFPR should fix your problem.

 

[turbodsm18]

You cannot run anything above a 190lph with your stock FPR. The pump will overrun the stock FPR and you'll just be dumping fuel into your combustion chamber. So, like pitbull419 said, SAFC and AFPR should fix your problem.

You can run a 255 on the stock fpr. It will run rich but it will run. Being that the car has a keydiver chip, it should have enough tuning on it to idle properly.

It seems to me like you Mass air is crap. IF I recall correctly, the MDP (manifold Differential Pressure) sensor takes over if your mass fails. So in theory, when you have the mass plugged in, the ecu is reading from that, which is why your car wont idle. Now when you unplug it, you get readings from the MDP sensor, which will make your car idle but I doubt you will have any power what so ever.

I would suggest swapping the mass air with a known working unit and trying again.

Also, you mentioned that the car has sat for a few months, you may want to drain the gas and add some fresh stuff according to what your tune is for.