I have a 1990 302 in a bronco. It will not Idle well. It sounds good at Rpms over 1000 but anything below that it hunts up and down til it dies. I have replaced the upper intake gasket,throttle body gasket, all the vacuum lines Spark plugs and wires. I dont know what else to look at. The check engine light is not on. i also changed the fuel filter and put fuel injector cleaner in it. Let me know what I should look for next please. I rebuilt the engine. All the gaskets are new.

 

Is it safe to assume since you were able to rebuild the engine you have the timing set correctly?
If you spray some carb and choke cleaner in the intake does the idle improve any?

 

Yes the timing is set but it is set at 1000rpms. That is the lowest I can set the idle to keep it running. I haven't tried adding anything to the air to help it burn. I have good fuel pressure. I have rebuilt engines before but I have never changed this much to the bottom end. Someone told me today, that the bigger cam messed up the computer and I need to reprogram it.

 

Ahhh, you didn't tell us you changed the cam from original.

 

The cam I installed is only slightly larger. I didn't think it would make that much difference. I talked to some friends today and they dont think It needs reprogrammed which puts me back to being lost again. Any tips?

 

This is going to be tough to explain. These throttle bodies wore over time, and after all the years I have in the business, I'm (to this day) torn on wheter to clean them or not. It seems if I clean them, they wind up with this problem.
Best way to start is to backprobe the TPS wire, Which I believe is like black off the sensor or something like brown or black with a (faded)tracer. It should be sitting right about 1.0volts. Start the engine, and snap the throttle a few times, and see if it returns to within 0.10 volts of the original voltage. If not, the throttle body is worn, which will create a hunting or surging idle. The problem is, most of these are not availbile any longer.
If this is like an RV cam, then it shouldn't make much differenece. If it's bigger, then the rough idle might be something you'll have to live with.

 

I know its been a while. I was busy and haven't had time to mess with the truck. It is just an RV cam in the truck. That's why I didn't believe the the computer needed reprogrammed. How does the throttle body go bad? Would it just be the throttle position sensor? I have put on a new idle air control valve. The engine still surges. I have the idle turned down to about 800 rpm's which is close to what it is supposed to be but it still hunts and I am not sure what else to do. If you have any more incite please let me know. I have found new throttle bodies for this engine but they are $350.00. I don't want to just buy one on a hunch. One more thing I have noticed. When I drive the truck and I come to a stop sign, when the truck is down shifting, right when I stop the engine goes to 500 rpms and about dies. It never dies. once the trans shifts down the idle goes back to "normal". If I shift into neutral it doesn't do this. I believe this is a separate problem with the trans but I thought I would through that out there. The trans needs some work too. thanks

 

got to ask does the exhaust smell of gas? 'rich' if the cam you have is a little bigger and longer duration it's idleing rich and needs more air hope this help's.

 

Yes it smells rich. It definitely wants more air. The only problem is its fuel injected and computer controlled and I dont know how to adjust the air fuel ratio on this engine.

 

Can you bump your timing back bit might help. it's loaden up with fuel