got a picture?

 

ISC-BPA is the same thing as IAC. It's not a sensor, but a solonoid that controls idle speed. If the computer is changing the idle speed, it means that the valve is working fine.

 

Sorta kinda.....unlike say a GM version that uses an actual stepper motor to alter the throttle plate, the ford ISC-BPA is 2 distinct entities - the ISC is a solenoid that actuates the air bypass valve (Id call it a ABV, they call it a BPA) which is simply a small passage that gets opened and closed real quickly at idle via the solenoid - the more cycles (as you can measure via a DVOM) the more it is 'open'

anyways, fords are famous for coking up the intake manifolds and plenums during hot soak, this crap interferes with the pintle in the BPA such that the ECM tries its little heart out to keep a smmoth idle, but due to sticking, the ISC is varied from periods of real high cycles to periods of real low cycles, as measured by the ECM from MAP readings. Your idle as you can imagine is just as wild.

Many many many TSBs have been issued about this...to avoid cleaning it so often, ford came up with an aluminum spacer, 2 gaskets and longer bolts to move the BPA off the intake - a bandaid, its not rocket science to clean. Every 30-50K should suffice when you are doing general maint.

 

ISC = Idle speed control BPA = bypass air solonoid IAC = Idle air control All the same thing, just different terminology. Referring to Fords here. He's replaced the thing 3 times, so I don't think that a dirty valve is causing this problem. We're both referring to the same thing, RTM was just confused by what you called it.

 

lets not abandon this just yet.....did he replace the ISC or the BPA? IIRC ford sells them separately....is the BPA new and or cleaned?

 

I have an 85 Bronco II with a 2.8, feedback carb, and it uses an ISC motor to control the idle. I can't find any good information on how to adjust this darn thing. I tried what information I have but it doesn't seem to get it done. The thing idles great until the ISC died. I replaced it with a new one and it would run the idle to about 3500 each time the vehicle came to a stop. It would stay there for a couple minutes then run down to normal. At other times it would stall at idle. I set the idle final stop at an idle of 850 so the engine doesn't die. This little item is how Ford controls the dashpot also. I am positive that what is going on is this. When I let off the gas the dashpot signal from the computer to the ISC is not correct? This cause the problems. I have a new tps sensor on the carb and the carb was rebuilt after the problem appeared.
Anyone know exactly how to set this up correctly? By adjusting the position of the isc it seems to give other issues. I managed to get rid of the hi 3500 rpm issue. My thoughts are that the computer looks at the TPS then looks at where the contact is made on the ISC to control things. If the ISC is not set in exactly the correct spot the computer causes these funny things to happen. Service adjusting procedures on this are not listed in any service manual I have.
Anyone that has any info please help??