1986 Ford Ranger 2.9 idle issue

[RangerTony]

Hello all, and thanks in advance. I really need some help, and it's getting down to the wire. I've had my '86 Ranger here in Reno at Greg's Garage for almost a month. The tech there can't seem to figure out what the idle issue is, and nor could I. I'm nearly ready to take the truck back and try again. Here's the symptom: It starts up great, warms up, and then the idle goes buggy. Yeah, first thing that comes to mind is the IAC. I've tried two after market units, and because I was told there's a potential problem with those in the electrical circuits, I went to the salvage yard and got a Motorcraft unit. That was over a week ago, and I haven't heard from Greg's Garage. This engine has 10K on it, and I've replaced the following: O2 sensor, IATC sensor, MAP sensor, Fuel Pressure Regulator, high-pressure fuel pump, Throttle Position Sensor, ECM, Ignition module, rotor cap... (I hope I didn't forget anything). I'm thinking there may be a bad wire to a sensor, and I did make the mistake of piercing (slightly) the wires to the TPS and the IATC, and the MAP sensor, and read voltages that seemed to be okay. I don't know if I should dive into the wiring and unplug the sensors and search for a break.... or what? I need this truck before the rain comes. My emergency car is a convertible and the top is shot. Thanks for any help you can offer.

Tony



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[rusty ol ranger]

Scan for codes, go from there.

Does it run good once your above idle? Or does it run shitty through the whole range?

If it does it could be the coolant temp sensor.

 

[RangerTony]

Thanks for asking. I replaced that sensor with a new one from NAPA. It will run great on the freeway. It's at stoplights and such after it warms that I'm in trouble. Then, once I restart it, it will run good for a little bit (I assume the computer is running it on presets)… after a few minutes, the same thing.

 

[rusty ol ranger]

Run your codes. See what you come up with there.

 

[BlackBII]

If the idle is too high then extra air is getting into the intake manifold somehow. I imagine you've checked for vacuum leaks and the like, so it's possible the IAC is opening too much once it's warmed up.

Are you sure the throttle body plate isn't getting stuck open or something similar?

While it is idling high, unplug the IAC. The engine should die or come very close to it. If it doesn't, then you know air is getting in somewhere other than through the IAC

 

[alwaysFlOoReD]

I had the same problem with my 86. I never did figure it out before it died. But since then I've read about the pcm capacitors can be fubar. Replacing the caps if there is signs of leakage or swelling may work. Or try with a known good pcm if you can find one.

 

[Oxxon]

Hello and welcome to TRS!

 

[RangerTony]

Thanks for that. I had found a PCM on Amazon, back when I had another issue when I put in the engine. I've swapped it back and forth a few times as I've been frustrated. The deal is that I did run codes before I took it to this shop, and came back with the number for a grounded spout circuit... and also pointing to that 22K resistor in the RPM circuit. Replaced the resistor. I did see some breaks in that wire; it may have grounded out two PCMs???? Is that possible?

Thanks all for this. I have left a message at the shop and figure that I may have to take it back myself. Oh, when the IAC connector is pulled it does drop the idle... at least it did when I took the truck in. I'd sure like to get the old girl back.