high idle, cuts out
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high idle, cuts out
I have an 86 f150 5.0 auto 4x4. I just bought this truck and am trying to work out all gremlins. It wants to idle at about 1500-2000 rpms and after it is warm it wants to cut out while driving, almost like its running out of fuel. As soon as you let out of the gas its fine, but if you stay in it it bucks and jumps and will eventually fall down to an idle even with my foot flat on the floor. I pulled codes and got a 63 and 31. I changed the TPS for the 63 and it didnt change anything. My gut tells me fuel filter, but im also not sure about the 31. I had changed a broken battery cable and tightened up alot of loose connections on the solenoid and that cured it for about 20 miles. Any suggestions? Thanks in advance.
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Looking at the idle screw it doesnt look like the factory screw. I think somebody may have been messing around trying to compensate for some other problem. Going to try to get it back to factory setting and go from there.
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Found all kinds of fun stuff lol. Went to reset the idle and found the top screw for the IAC was stripped and i could move it by hand. Pulled TB tapped the hole and repaired that. Also cleaned the IAC while I was at it, but it was clean as a whistle looked pretty new. Brought the truck up to operating temp, pulled the plug for the IAC and backed the screw all the way out, truck never died. So I am assuming somewhere there is a vacuum leak. Checked and checked and couldnt find anything. Also found main ground wire had been cut in two and taped together. Built new cable out of 2/0. After all that, it is definitely worse. If you give it any pedal at all it just bucks and jumps like you are getting on and off the throttle real quick, but will only do it while its in gear. In park or neutral it revs fine and sounds strong. Still have 63 and 31.
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Why do you still have 63? Have you checked for the proper voltage at the TPS? The power supply for the TPS also serves some of the other sensors, so if you have a bad wire that might be the source of the other code or codes.
It stands to reason if the computer does not know that you are pushing on the throttle, that it's going to hesitate when it suddenly sees all that air coming into the engine with no warning from the TPS.
It stands to reason if the computer does not know that you are pushing on the throttle, that it's going to hesitate when it suddenly sees all that air coming into the engine with no warning from the TPS.
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I ran out of time today, but first thing in the morning im going back out to back probe the tps and see what its reading. Thats what i should have done first, but I always have to take the long way around lol. I believe that my original TPS was somewhat out of range and the new parts house (non motorcraft) one is completely off the reservation. Thats the only thing that makes sense because the original one was more intermittent and the new one is constant. Any reason it would only do it in gear and not in neutral or park? Thought that was odd. And i appreciate the help by the way.
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There is no load on the engine in neutral or park, so the engine spins up more easily with less throttle opening.
The engine always wants the air and the fuel in a ballpark ratio to run correctly. When you suddenly open the throttle, the computer instantly adds more fuel by keeping the injectors on longer, in anticipation of more air entering the engine. The computer also goes by rpm, temperature and vacuum levels to adjust the air to fuel. Right now in your situation, that is the only thing it can go by, and it's a day late and a dollar short with no TPS info.
That's also interesting that you could not get the engine to stall when the throttle is closed all the way. You are correct, you are getting air from somewhere else. So fix the TPS problem first, but keep in the back of your mind that you have air coming in from somewhere also, maybe your IAC is not working correctly either. It routes air around the throttle plate.
The engine always wants the air and the fuel in a ballpark ratio to run correctly. When you suddenly open the throttle, the computer instantly adds more fuel by keeping the injectors on longer, in anticipation of more air entering the engine. The computer also goes by rpm, temperature and vacuum levels to adjust the air to fuel. Right now in your situation, that is the only thing it can go by, and it's a day late and a dollar short with no TPS info.
That's also interesting that you could not get the engine to stall when the throttle is closed all the way. You are correct, you are getting air from somewhere else. So fix the TPS problem first, but keep in the back of your mind that you have air coming in from somewhere also, maybe your IAC is not working correctly either. It routes air around the throttle plate.
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Thanks for the info, its always nice to have somebody to bounce stuff off of. Whatever comes up tomorrow ill be sure to post it, I have searched through a ton of threads with problems and no solutions lol.
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Alright, back probed the new TPS and it read .2 to .1 and never moved. Took it off because i thought maybe i didnt get it engaged with the TB, but no it was bad. Swapped it out and new one read .86 closed to 4.78 wide open. Also found that the high idle was gunk buildup on the Tb blades that wouldnt let it close all the way, and the return springs werent strong enough to close it all the way. Cleaned the gunk out and added a helper spring. Ran like a champ and the 63 went away. Still have the 31, but ill work it out later. Then i ran out of gas lol.
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