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1993 F150 Transmission Problem

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Old 03-26-2009, 02:10 PM   #1
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Default 1993 F150 Transmission Problem

Hello,
I am having a problem (well problems) with my truck. It is a 1993 F150 5.0L automatic. Today on the drive into work, I was going down the highway at about 65mph. I went to pass someone and stepped on the gas. The RPMs went very high, and there was no acceleration, in fact, I began to decelerate. It seems as though it isn't shifting. If I get down to about 20 mph and then step on the gas it accelerates, but doesn't shift. As soon as I stop accelerating, it again only revs until I get down to about 20mph, where again I can accelerate. This is a big problem, and I am hoping it isn't the tranny itself. There wasn't any noises, no grinding, no trouble shifting before this.

Prior to this problem, I have been battling an idling problem. The truck would idle down, then rev up, then slowly come down, then rev up, etc. It does this more frequently if there is a load on the engine, for example turning on AC or turning the wheel (power stearing pump). If I disconnected the IAC, it would kill. The idle would also drop so low that it would almost kill. I changed the IAC, the O2 sensor and took the throttle body off and cleaned that. I should have changed the TPS while I had it off, but didn't. Now it runs when I disconnect the IAC. It still revs, but never gets down almost killing anymore. Now it goes between normal idle and high. If I disconnect the IAC it seems to not jump around. Also, I noticed that on the throttle body, if I disconnect the vacuum line coming in and plug it with my finger, it also seems to run fine.

I am wondering if both of these problems could be related. Vacuum leak? Unrelated? I tried the propane method of looking for vacuum leaks. Didn't find anything, but it is hard to hear any propane induced idle change when the idle is changing all the time anyway. I had it into a shop and they couldn't figure out the idle thing either, and they said they checked for vacuum leaks (all of the troubleshooting was before the shifting problem, which started about 1 hour ago on my way into work).

Thanks in advance for any help!
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Old 03-26-2009, 02:14 PM   #2
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Oh, and the engine light appears to be out as it doesn't light when you just turn the key to on. I bought a code reader and the only thing I get is a 12, Idle too high, during the KOER. Again this was done before the shifting problem started.
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Old 03-26-2009, 03:05 PM   #3
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sounds just like the problem that I had a couple of years ago I have a 93 F150 5.0 auto e4od tranny the shop said it was the transmission selector switch it cost about 75.00 dollars to fix hope this helps
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Old 03-27-2009, 12:47 AM   #4
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Code 12 isn't idle too high, according to my F150 book it is RPM unable to reach upper test limit. According to my generic code book it is cannot control RPM during high RPM test. It could be a possible fuel problem. Check the fuel pressure and if the fuel filter hasn't been changed in a while I would change it. Also test the TPS.
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Old 03-29-2009, 11:34 PM   #5
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i had a similar problem and it was the tps that was throwing it all out of sync
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Old 04-05-2009, 11:26 AM   #6
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Have you figured it out yet? If it has the AOD transmission ( you can tell if it doesnt have an OD off button on the end of the shift ) it may very well be that the plastic retainer has broken off of the line pressure control cable that attaches to the throttly body. It's a fairly common problem on all of the models that use the AOD, not just isolated to the trucks. Shoot me a PM if I can help you in any other way.
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Old 04-06-2009, 10:54 AM   #7
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Thank you for all of the replies. I incorrectly said code 12 before, it was actually code 13.

I read the codes again following the transmission problem developing. I did get a code, can't remember the number, but it indicated that the voltage from the TPS was too low. I replaced the TPS, but in the process, found that the cable from the throttle body to the transmission had broken off (plastic broke). The new TPS did not fix things so I took it to a transmission shop. The truck does have the AOD transmission and they said that driving it without that cable attached causes the transmission to burn up and that mine needs to be rebuilt . Very frustrating.
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