Ok, my 92 F-150 is giving me more grief. I posted in uncle Bobs thread about fast idle problems on a 5L. I pulled the codes today and came up with hard fault codes of 12 and 13 during KOER. Seems the ISC may be bad. Is this ISC the same as a IAC? Next I got a momory code during KOEO of 34. This is something to do with EGR. Seems Ford has 3 different EGR systems. A EVP,EVR and PFE. How does one identify which EGR system I have. I did a search for EGR on this site and came up with nothing. Any help would be appreciated.

Trevor

 

check or replace your IAC first, the other code may go away. If the IAC is faulty and you replace and the egr code still exists then do a test on the egr sensors. I just had a similar problem with an egr code and come to find out my evp was bad (on top of the egr valve). I was unable to get the right code that directed me to the evr, until I found the evp to be faulty. When the evr code came up I discovered the problem of the evr was the vacuum line to it was faulty. So you may check the resistance across the evp and see what you get, and look for faulty vacuum lines. I was unable to hear a leak I had to isolate each line and check for pressure psi. You are in an odd situation if the egr valve is stuck open then it will idle high as the engine sees a leak and is trying to compensate for additional air or the IAC could be bad. See what the IAC test looks like and post.

IF you don't have a haynes I will post what it says.


To check the IAC (or BPA-ISC, same thing different name). Turn key on but don't start. Probe the harness to the sensor from the pcm with a voltmeter you should get 10.5 volts.

States next remove valve and clean the pintle of excessive carbon also clean the IAC valve housing to remove deposits. Do not soak part in cleaner or anything. Check the "O" ring for hardening or deterioration, may need to replace. States you can use carb cleaner, but I would at your own risk.

check resistance of the BPA-ISC with electrical connector disconnected, check the resistance of the valve, it should be between 7 and 13 volts.

Good luck

 

Netops, JWTaylors' advice and direction is sound. But don't get into replacing all the components that can control your idlle without first knowing that they are defective. Cleaning the ISC control valve is a good start and a probable offender. The EGR valve can be evaluated by applying vacuum to the valve while the engine is running at idle and listening to an rpm change. You can also see the acutator pin moving by shining a light through the bottom side of the EGR valvle. I suggest that you invest in a Haynes manual, Ford Pickups & Bronco 1980 - 1996 (#36058) and follow the detailed troubleshooting instructions for each of the potential problems. I replaced my ISC valve and found out later it was ok. My fast idle problem ended up being two-fold; a slightly out of spec. Idle Speed Sensor and a faulty coolant temperature switch. Hopes this helps.

 

Well for the price of a new IAC at $180 Canadian. I wont be changing it unlees I know for sure it is faulty. Tomorrow I will take the voltmeter out and try the tests that JW mentioned. I'll let you know what comes out of it. Maybe I should leave my 92 for dead and start running my 68 F-100 daily. Cheap and easy to fix!

 

Ok, I ckecked out the IAC and I think it is ok. I had the correct voltages when I back probed the connector. I also get the right resistance across the IAC motor. I read in a tech note about taking the IAC off the TB and plugging the holes. It said if the idle returned to normal. The IAC is bad. It said if the idle stayed high. Then chances are I have a bad vacuum leak. I tried this and it did not make any difference. I understand that 302s have a problem with the gasket between the upper and lower intake. This tech note mentioned about removing the air intake hoses from the TB and plugging the 2 intakes. If it stalls then it is tight. If engin keeps running. Then I have a bad vacuum leak. Any advice on this trick? I am thinking vacuum leak as I remember hearing a "putter" sound a couple of times in the past when first starting (not always though). It would go away after few minutes.

Thanks

 

Check you rubber air intake tubes feeding air to your throttle body. When you takes these
off and on it is possible to rip or split the edges when you reassemble to the throttle bore and it not be noticable. If these are taking in air, it will idle fast because the air leak is by passing the air mass flow switch up stream. I have had this to happen.

 

Problem solved! Turned out to be the gasket between the upper and lower air intakes had sucked itself in. I showed it to a freind and he said it had been deterating for awhile for what was left of it. Anyway, thanks to all who offered assistance.