Okay, I haven't been here for awhile. Fortunately, only minor problems. Unfortunately, other people ask "smart" (?) guys for help, who in turn know when to and who to ask for help. My brother has a '97 F150 SC, 4.6L, probably 4R70, and ~180K. Usually runs fine. He's a military mechanic and works on big Hummers and aircraft etc. His e-mail is out (and I have problems at the dial-up ISP level-it's late) and he lives 300 miles away. Best I can tell (by phone) is that his truck runs fine in Park and neutral but in Drive, it idles too low or stalls. I asked if he could run codes. No engine light is on. He said he could accelerate and get the truck to move in Reverse but couldn't go forward to get to a shop. He may have a friend who could run diagnostics in the driveway. I'm not real familiar with this truck. I thought about vacuum leak, or TP, or torque convertor clutch switch (CCC-convertor clutch control solenoid) but I don't know where to look or to advise. I tried a search but only a quickie. I'll talk to him again by phone tomorrow or rather tonight, now. Maybe someone has experienced or heard of similar problem/symptom and can point me in the right direction. I have the Ford service cd-rom but it's not much use for diagnostics without codes. Truck was running fine last weekend because he drove here and back. Wouldn't think it would be trans. related either. Possibly IAC or similar? Hopefully, this is enough info., if not I'll try better later. I haven't been able to stay connected very long tonight. Thanks for any insight/assistance, Tim

 

I would suspect either a vacuum leak or a stuck IAC valve.

When the transmission is put into gear, the computer commands the IAC to open more (raising idle speed) to compensate for the added load of the slushbox.

Since the IAC valve is a computer-controlled vacuum leak, I'd try cleaning it if no other vacuum leak is found. Cleaning sometimes helps if they are sticking due to deposits.

Steve

 

See if it will stay running in gear if he holds his foot on the gas a little. If not, it could be a stuck TCC. If it stays running, then I would suspect the IAC or a vacuum leak as mentioned above. Check the PCV hose (especially behind the intake) and the intake hose between the throttlebody and the MAF.
You could also try cleaning the MAF and changing fuel filter.

 

Thanks ya'll. He cleaned the IAC but no difference. Told him to get someone to run codes. A scanner should be able to engage/disengage the TCC solenoid. But I'm unsure where it is located on the 4r70w. May have to change torque convertors. Correction, the truck only has 150-160k. He's gone for reserve duty this weekend but will be off Mon. and may get to look further.Thanks again.

 

Did you ever diagnose the prob? I'm having the same issue with the same truck.

 

He changed transmission fluid (no filter, suction method) and I told him to change the screen. A month later they changed filter and oil and added Lucas to the trans. Each step he made gave improvement and last I heard (couple months maybe) it's running like it used to. Lucas is an oil additive, in case you're not familiar with it, primarily used by diesel equipment mechanics to enhance oil properties like clinging to parts. it comes in gallons and smaller sizes at most parts stores but probably isn't what the auto manufacturers would recomend. They'd rather their dealers get the repair jobs. I've never used Lucas in an auto trans. but in engines and such I've never had anything bad happen due to the Lucas. As for the transmission it could very well have been a stuck TCC. New buyers get away with "neglect" but when one of us gets their trade in, we have to pay for it. I put a TransGo kit into my E4OD last winter and checked the inside good. I'm not a transmission guy, just don't like walking. Sorry I don't have more details. Posting, reading old posts, searching, etc. helps give insight on diagnosing and correcting most problems. And it's cheaper than slapping on parts or running it to a shop. Good luck.