Erratic Idle
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Senior User
Joined: Sep 2003
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From: North West Florida
Erratic Idle
My 86 Bronco II has a problem with idle. After warm up the idle kicks down to around 1400 rpm. After additional driving the idle will move down to 1000 RPM. It's supposed to be around 800 RPM. The idle will wander on occasion by a few hundred RPM up or down. This makes the vacuum reading wander between 17 and 20 inches. The Haynes manual wants to check every flippen thing in the circuit. I know it's just one probelm causing this. Any ideas out there?
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Joined: Jan 2002
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From: Monument, CO
Clean the IAC; disconnect the wire to it and see if the idle changes (it should); check for vacuum leaks; check for codes. Is that every flippin' thing?
Mine runs at 1500 or so for a few seconds when first started, then drops to around 1100 for a couple minutes. After 4 minutes or so, it idles at 800. The only problem I've had that affected the idle speed was a bad ECT sensor (engine coolant temperature). That made for a consistent high idle because the computer thought the engine was always cold.
Mine runs at 1500 or so for a few seconds when first started, then drops to around 1100 for a couple minutes. After 4 minutes or so, it idles at 800. The only problem I've had that affected the idle speed was a bad ECT sensor (engine coolant temperature). That made for a consistent high idle because the computer thought the engine was always cold.
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From: North West Florida
Well that figures. My temp sender is bad. I was going to change the gauge to a manual type. I didn't know that the computer got temp info from that sender that also feeds the temp gauge.
And IAC? What is that? And I have no codes. Being in Florida the engine warms up fast. It idled at 1000 rpm's all day untill I got the A/C working, then the idle dropped to 800.
And IAC? What is that? And I have no codes. Being in Florida the engine warms up fast. It idled at 1000 rpm's all day untill I got the A/C working, then the idle dropped to 800.
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Joined: Jan 2002
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From: Monument, CO
If it's the ECT (as Ken00 said, NOT the same as the gauge's sensor), the computer should show a code for "ECT out of range" or something similar. But take the IAC off and clean it up first. It's the horizontal cylinder mounted near the top of the upper intake on the passenger side.
If you have to replace the ECT - a word of advice. Grab the vaseline and go to the dealer.
When my ECT went out, I went down to Pep Boys and bought another one. The old one was all metal, bronze colored. The new one was plastic. It lasted 6 months. Then I went to NAPA and paid more money for their ECT. I asked if they had an all-metal one. Nope, just this plastic one. It lasted 6 months. The third time, I went to Ford, paid an obscene amount of money and got an all-metal, bronze colored ECT. It's lasted over a year so far.
If you have to replace the ECT - a word of advice. Grab the vaseline and go to the dealer.
When my ECT went out, I went down to Pep Boys and bought another one. The old one was all metal, bronze colored. The new one was plastic. It lasted 6 months. Then I went to NAPA and paid more money for their ECT. I asked if they had an all-metal one. Nope, just this plastic one. It lasted 6 months. The third time, I went to Ford, paid an obscene amount of money and got an all-metal, bronze colored ECT. It's lasted over a year so far.
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