View Full Version : Idle Problems

12-31-2007, 08:18 AM
I recently put a new engine in my 93 sc- it was modded a little- 42lb injectors, rougher cam.... I reprogrammed the computer with an MN12 tuner. Car still does not idle. Upon starting, it idles up to about 2000 rpm and then drops immediately and stalls out. I have used a code reader as the check engine light came on once and went back off- but it does not read any codes at all. My question is: Is it a sensor (TPS, or Crank ~~~ Sensor) or am I not getting enough fuel. It is driveable if you keep your foot on the gas but terrible to try and keep running. If anyone else has ran across a problem like this and can help I would greatly appreciate it. Thank you

12-31-2007, 09:46 AM
How does the car smell when you start it up? Very strong gas smell or more like a bunch of rotten eggs?

What parameters did you change in your tuner to support the injectors?

12-31-2007, 11:51 AM
I do have the "rich" smell to the exhaust, but it did the same thing before I reprogrammed it.

01-01-2008, 09:26 AM
From vague memory the "cold start table" may need some work.
(assuming you have already modified the starting crank pulsewidth)

Also, you could fine tune with the injector battery voltage offset in
the range under 12 volts. (assuming MAF curve is ballpark)

You could take a voltage reading off your narrow band O2 sensors, and see
if it pegs high(rich>.5v) or low(lean<.5v) at idle?

01-01-2008, 10:23 AM
Can you get your car up to running temp, and does it improve as it warms up?

As mentioned, you can measure the voltage of the O2 sensors, and if all is reasonably well, at startup it should stay pegged rich which is >0.5 volts for the first 30 seconds or so. Unfotunately you won't know if your really rich or somewhat rich as the narrow band O2's can only let you know if your around a 14.64 AFR, which at startup should be around the 11 range I believe. If the sensor swings to near 0 volts then your leaning way out, which can be fixed with the injector low slope and breakpoint. (I also recommend you consider getting yourself a WB O2 if you want to do your own tuning)

Could you post what injectors your using, like Lucas or whatever. Also post your injector high & low slopes, injector breakpoint, injector offset to battery voltage, CID (engine displacement) and your crank fuel pulse width vs ECT function as well.

Also, are you still using the stock MAF in the car?

01-01-2008, 03:15 PM
Have you checked for a leak in the IC tubes? Had the same problem as I had left one of the nuts loose and the engine would not idle for long and it was very rough.

01-03-2008, 07:28 AM
I replaced the tps and still have the same problem...... I apologize, but a lot of this stuff is greek to me. I am used to working on a 57 t-bird, and this has a lot of electronic stuff I am not up to par on yet- which frustrates me. I checked for vacuum leaks, and made sure my tubes were sealed- is it possible that the fuel injectors are plumbed wrong? Should I put the stock ones back in?