TPS/Won't idle when cold

[Launchpad]

I posted this on the other mustang site with no responses, any ideas?

1990 with stock internals and 127,000 miles- Won't idle until warm, fires off and idle goes to about 1400 for a second or two, then pretty much dies. I can keep it running, runs like a carbed car. After about a minute, it will idle fine by itself.

I've removed and cleaned the salt and pepper shakers, the IAB, set the TPS to .98 at idle. ( goes to about 4.65 at WOT, regardless of where I set it? Is that normal?)

Cleaned the maf, unhooked the Batt for 30 minutes.

Still does the same thing, any ideas?

I've spent about 2 hours reading all the previous posts- thanks.

 

[jrichker]

See "Surging Idle Checklist for help with all your idle/stall problems. The first two posts contain all the updates to the fixes. I continue to update it as more people post fixes or ask questions.

 

[bloopbloob]

jrichker i'm disappointed! you didnt say dump the codes! I'd start with checking the codes. Check your egr and see if it holds vacuum too. Mine had symptoms somewhat like that when my egr went.

 

[Launchpad]

IAB

Is this a Ford part, or something you can get at autozone?

I'm a little fuzzy on the second part of trouble shooting the IAB. I tested the Red wire going to the IAB and got 12V, the next part says to test between the red and white.... When doing this, where exactly are the probes supposed to be?

Thanks-

Troubleshooting:
Using a voltmeter, look for 12 volts on the red wire for the IAB, measure between the red wire and the engine block. No 12 volts and the engine runs, then you have bad wiring or bad connections. A safety pin to probe the connections from the back side of the connector will be helpful.

Next measure between the red and white/lt blue wires: you will get a reading less than 12 volts but more than .5 volts. This is because the computer switches this wire to ground many times a second, creating a voltage that varies in average value. If you had access to an oscilloscope, you would see a square waveform that varied in duty cycle. It would switch from 12 volts down to 1 volt or less and then back to 12 volts.

If you have a small 12 volt test lamp, probe the red & white/lt blue wires. With the engine idling, the lamp will glow at less than maximum brightness. Use the red wire to power the test lamp and ground the other test lamp lead on the engine block. You will see just how bright the lamp glows. If the lamp did not glow when you probed the red & white/lt blue wires, then there is an open connection (broken wire or bad connection) between the computer and the IAB.

If there is a short to ground in the white/lt blue wire, the voltage will not go above the 1 volt point. There may be a bare wire rubbing against metal or the IAB may have an internal short between the case and the wiring inside it. The resistance of an IAB would typically run between 10-14 ohms across the two connections and open or greater than 1 Meg ohm between the case and either one of the connectors.

The IAC depends on the computer to provide a ground to make the IAC work. Bad wiring, dirty connections or a failed IAC circuit inside the computer can keep the IAC from adjusting the idle like it should.

 

[Launchpad]

Nevermind, went to Autozone and got a new IAC. Starts and runs perfect-

Thanks for the previous info-