After a full engine and trans overhaul I have a bad 500+ rpm intermittent surge.
A Snap On Vantage showed code 412 which has been resolved by a thorough throttle body and IAC cleaning. The throttle position sensor, knock sensor, and O2 sensor have also been replaced.
I've tried dis-connecting the battery several times for 10+ minutes and the last scan revealed no codes.
I have no clue as to where to go next. Any clues guys?
Dirk
What Ford truck are you referring too? engine size, trans type.
I had a similar problem with my 89 5.0. It turned out to be the fuel filters. I noticed you didn't say anything about changing it out.
Damn. You try and provide as much info as possible, and forget the basics ;-)
1991 5.0 AT 2WD
Take off and clean the EGR valve:
it might be stuck open a bit?
Refinish King
PS
How does a vantage read codes?
Mine doesn't, and you couldn't give me a Snap On Scanner. You can't do air bags, cycle any components like you can with an OTC or MPSI/Micro-Link.
Then you have what sounds like a vacum leak!
The IAC is going in and out to compensate, making the vacum leak seem more exaggerated when wide open, and less exaggerated when closed.
Time for a propane vacum leak tester, or a good grade of carb cleaner, spray with the air filter housing on, Then you won't get a false idle change when the mist gets pulled into the throttle body.
If this is not the case, check for an exaust leak near the exaust manifold to head surfaces, or the donut gasket or couplings at the flanges, before the O2 sensor. Leaks also let in air, giving the O2 a false reading. The pulsations of the cylinders firing on the bank where the exaust leak dray in air only when cylinders on that bank fire. Which may be the cause the lopey idle.
I hope this helps?
Refinish King
A vacume leak was my first thought, but the problem is very intermittent. After 2 0r 3 starts then the idle will go into the hunting loop, or, when it's doing it I can shut it down and start it back up again and it will do it again.
Try this then:
To set the base idle at the throttle stop, you have to remove the IAC and not set a code either.
Leave your scan tool hooked up. make sure the key is off, thexton makes IAC block off plugs, a good rag packed in without going into the small air intake will do fine.
Take out the IAC and put the connector back on it, Take the plug out of the throttle stop, and make sure the IAC is where it won't get damaged!
Start the engine with the scanner connected and make sure it's configured to that exact vehicle/engine combination. let the engine warm up, and now is a good time to see it the idle lopes, if not. This is your problem!
Set the base idle for 550 RPM after the engine reaches full operating temnprature. Then shut it, put a few drops of ATF on the IAC. It should be fully retracted at this point also. Reinstall the IAC, reconnect it and start the engine and repost the results.
Refinish King
MPSI/Micro-Link.
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