Cold start gremlin - Bad A9L maybe?

[vicster]

I have been having difficulty getting my 87 mustang to start in the morning from a cold start. When I turn it on, it will either die right away, or it will stumble around until it gets to operating temp and then will run fine. I have checked the ACT and ECT sensors and they are fine. Also, I cleaned my IAC, replaced my plugs, double checked my PCV, set my timing to 10 degrees, but still, it seems that I have no idle control. Some of my grounds were loose, so I retighten those. My MAF is fine as well as my TPS. I was wondering if my computer could have gone. My car was coverted some time ago to mass air, and currently I have a A9L in there. Fuel pressure is fine. What do you think?

 

[HISSIN50]

Have you pulled codes? WHen the car is hot and you turn on the A/C, does the idle drop and stay dropped?
Or if you unplug the IAC, does the car idle the same as it did connected. A clean IAC is not necessarily a good one.

Good luck.

 

[bsedwebt70-5.0]

I did about the same thing as you - ECT, ACT, Cleaned IAC, fuel pressure, timing, cap, rotor, plugs, wires, etc... I finally bought a NEW IAC from AutoZone and problem GONE for good!

 

[gojonnygo]

^^^ Iac.

 

[vicster]

I swapped out IAC's with my buddy's working IAC, reset the computer, and still having that problems. Grrr

 

[JB66]

You said the ECT sensor was fine. How did you check it and what readings did you get? Also, is your coolant full when cold? I've had new ECTs that have been bad right from the store...

 

[jrichker]

Code 21 – ECT sensor out of range. Broken or damaged wiring, bad ECT sensor. Note that that if the outside air temp is below 50 degrees F that the test for the ECT can be in error.

The ACT & ECT have the same thermistor, so the table values are the same

ACT & ECT test data:

Use Pin 46 on the computer for ground for both ECT & ACT to get most accurate readings.

Pin 7 on the computer - ECT signal in. at 176 degrees F it should be .80 volts

Pin 25 on the computer - ACT signal in. at 50 degrees F it should be 3.5 volts. It is a good number if the ACT is mounted in the inlet airbox. If it is mounted in the lower intake manifold, the voltage readings will be lower because of the heat transfer.

Voltages may be measured across the ECT/ACT by probing the connector from the rear. Use care in doing it so that you don't damage the wiring or connector.

Here's the table :

68 degrees F = 3.02 v
86 degrees F = 2.62 v
104 degrees F = 2.16 v
122 degrees F = 1.72 v
140 degrees F = 1.35 v
158 degrees F = 1.04 v
176 degrees F = .80 v
194 degrees F = .61

Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter.

Ohms measures at the computer with the computer disconnected, or at the sensor with the sensor disconnected.
50 degrees F = 58.75 K ohms
68 degrees F = 37.30 K ohms
86 degrees F = 27.27 K ohms
104 degrees F = 16.15 K ohms
122 degrees F = 10.97 K ohms
140 degrees F = 7.60 K ohms
158 degrees F = 5.37 K ohms
176 degrees F = 3.84 K ohms
194 degrees F = 2.80 K ohms