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Discussion Starter #1
Automotive idiot with frustrated mechanic is asking for advice on what could cause my wierd problem...
Here it is, When cold starting (worse when weather is cold and damp). The truck kicks out of high idle in a matter of seconds and loses rpms. If you try to hold the rpms up you will fail. Have applied gas when in a hurry (hold engine ~1500rpms) and you can watch the tach start dropping after a matter of seconds. Something is telling the engine to slow down. If you step on it quickly (too impatient for it to warm up) it will hesitate, backfire, and die when you let off the throttle. This only happens prior to warmup. Once the engine is warm, no problems.
No Codes. New TPS, clean throttle body, new Thermostat. 94 w/ 5.8. Good Fuel Pressure. Mechanic checked fuel pressure and codes last time it was at his shop overnight and he had a chance to witness the cold start. Haven't been able to get it back to him yet and he is confused.
This is becoming an issue as the wife may be driving the bronco soon and this would really drive her nuts. She is impatient and would most likely end up stalled in the middle of the road somewhere.
 

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Ex Navy Nuke
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My first thought was TPS or IAC. Even though the TPS is new test it anyway. Clean the IAC. Check for any moisture inside the dist cap. Since it only happens when cold maybe it's the ect sensor. Just throwing out a few ideas.
 

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Charlie don't surf..
'92 Ford Bronco XLT
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When was the last time you changed your plugs, plug wires, cap and rotor?
 

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Most Ford idle problems come from the IAC. It will never send a code, because it is an output device. I've never had any luck cleaning them, either.
 

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The Anti Yam!
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sysgeek said:
No Codes.
Was a self test actualy done or are you assuming there are none due to no check engine light.
(A common mistake)

On your 94 you should stll get code 111 if the system pases.
(You have 3 digit codes)



95_G&W_XLT said:
It will never send a code, because it is an output device.
But it can set codes that point ti the IAC

For example
12 = (KOER) Cannot control RPM during ER Self-Test high RPM check.
13 = (KOER) Cannot control RPM during ER Self-Test low RPM check.

Both of these codes could indicate a problem with the IAC
 

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Banned
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Output devices do have fault & failure codes, like 415, 416, & 551.

Backfiring is generally a sign of a lean condition, or advanced timing. Make sure it's set to 10°BTDC according to the instructions on the emissions label under the hood, and test the ECT & ACT.
 

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Discussion Starter #7
thanks for the responses, I will pass these on to my mechanic.

I had a full tune up about 6mths ago. Plugs, wires, the works

My saying no codes, means that the scanner didn't report anything negative

it's started doing this in late aug and has only gotten worse since. It runs fine once warm, so I was leaning toward the IAC. It's about the only thing left that I can think of.

I hope to get it back down to shop this weekend, I'll let you know what they say.
 

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I have found that about the only codes you will ever get would be if the ckt is open or shorted. I one time saw a code 124 for tp greater than expected. I have changed a number of IACs without getting a code for the IAC itself.
 

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The iac can become "gummed up" with the oil film that is puked into your oem airbox by the crankcase vent. the only thing that has worked for me in the past was to replace the iac. i have also cut old ones up to determine the cause of the "failure" and have found that some of the internal windings can become so hot that they internally cross connect, not short in the general term but also not move the plunger in and out when they are supposed to and still check out ok on a code scan. i have replaced 3 on my bronco at approx 80,000 mile intervals. now that i mention that it does tend to linger no high idle now.....
 

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green ones make me horny
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You can test the IAC with a nine volt battery. just take it off and hook up leads to it and then to a 9 volt battery you will here a "pop" and if you dont here that it aint working.
 
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