RPMs Dropping When Stopping - 4.6L

[PotatoExplorer]

Ah, the Burgundy Potato saga continues!

This doesn't happen all the time, but I've had 3 instances in the past week where this happened - I'll come to a complete stop (or 1 time I let off the brake to press the accelerator to merge into traffic) and the RPMs will dip down from idle (700-800ish) to below 500 and almost feels like it's going to stall.

Some back story -
One day I drove 20 miles away, parked for a few hours and was getting ready to leave. I turned the car on with no problems. Then about 30 seconds of idling the orange wrench came on. I was thinking it was linked to my other issue (http://www.explorerforum.com/forums...r-maybe-torque-converter-clutch.372634/page-5) so I wanted to drive it long enough to hopefully have a solid check engine light. Got home, shut it off, turned it back on - orange wrench gone... wtf.

Got up the next morning to leave and the orange wrench again, only this time it was accompanied by the CEL. Drove to Autozone to have the codes read. It was determined that it was a Throttle Positioning Sensor. This is funny since I replaced the entire throttle body with an Autozone unit since I completely F-ed up my OEM one. The Autozone unit came with the TPS and all the other bits and pieces. Meanwhile the RPMs dipped low enough for it to shut off while in the parking lot. Started back up with no problems.

Later that night I moved the car to my back driveway and the Explorer failed to accelerate. I had the gas pedal pegged to the floor and it just creeped and crawled. When I went to round a corner the drivetrain sounded awful. It sounded like the brakes were popping on and off all on their own. Eventually it completely stopped even with the gas pedal all the way down. I turned the car off and back on and I regained all power.

The next day I replaced the TPS sensor with the one I had on my OEM throttle body and everything was back to normal except the few instances where the car felt like it was going to stall out.

Anyone might have any ideas where to even begin???

 

[tripplec]

Although a fuel filter on its last legs should affect high speed driving and/hard acceleration as both demand high fuel flow through it. If its the original I'd replace it to rule it out. The labour to get it out is likely the worst part of doing it as they should be fairly cheap for an OEM one. I wouldn't go aftermarket unknow brand on it. Some have a regulator built in. Getting a pressure test if you have shrader valve on the fuel rail wouldn't hurt to see how the pump is doing.

This is more process of elimination as to the cause. It depends and if you caught the correct code when the light came on. Maybe you should get your own code reader. I have Scangauge II myself with also works as a function digital gauge monitoring various computer status registers.

 

[Explorer_PL]

Hi Burgundy Potato -
Maybe this will help somewhat:
For few years I was trying to figure out why my 4.6 would stall after coming to a stop after driving down a long hill with a stop sign at the end. It was always the same down hill, about a 1/3 of a mile long. Then it would just die. It did it it to me on some other occasions, but because it would do it maybe few times a year, I did not know where to start and never followed on that. Than, another problem started, but I did not connect those 2 initially. On every stop sign or red light, the RPM would drop to 400-500 rpm and the engine would start making clattering noise and sometimes would stall completely. I'd get 0101 error ( IIRC) and I replaced the MAF sensor without any cure. But on a highway, while driving, it would be smooth like a new car.
When the car was barely driveable in the city, with lots of stopping, I had enough.
**********If you read my story before, sorry to bore you, but maybe others did not.....
I took it to 2 different shops and both told me to get a new engine sine the old one had 200k miles. They also quoted me between $ 4 and 7 k for a used or brand new one from Ford. I said both: thanks a lot.
Got a used motor for $ 1600 with 55k miles and dropped it in. Started it up and it was making same noise as the old one. Took it to Ford who diagnosed a locked up torque converter. Got a new TC from Ford for $ 300 (remanufactured one), and the problem was solved.

Now, when I think about it, those random stallings at the beginning was same problem. The TC was not unlocking when I was coming to a stop and chocking the engine.
When they did the diagnostic, the tech showed me some graphs of engine rpm's versus tranny and TC rpm's and you could clearly see the issue. The input and output rpm's of the TC were the same all the time.
Good luck.

 

[PotatoExplorer]

Hey guys, thanks again for your comments. They are very much appreciated.

Although a fuel filter on its last legs should affect high speed driving and/hard acceleration as both demand high fuel flow through it. If its the original I'd replace it to rule it out. The labour to get it out is likely the worst part of doing it as they should be fairly cheap for an OEM one. I wouldn't go aftermarket unknow brand on it. Some have a regulator built in. Getting a pressure test if you have shrader valve on the fuel rail wouldn't hurt to see how the pump is doing.

This is more process of elimination as to the cause. It depends and if you caught the correct code when the light came on. Maybe you should get your own code reader. I have Scangauge II myself with also works as a function digital gauge monitoring various computer status registers.

I replaced the fuel filter with a Motorcraft version about 1,000-2,000 miles ago. It was dirty as hell (it's actually documented in that link to the other thread with my other issue).

Explorer_PL - It's weird, everything keeps on pointing to the torque converter, even with my other issue linked in my first post. This very well maybe the culprit.

Another issue just appeared that may be related but I'm not entirely sure. Now under normal acceleration from a dead stop the Explorer sounds like is sucking in a ton of air. The RPMs seem to also be climbing higher than normal. After it gets up to about 3rd gear, the sound stops. It's sounding like the fan?? Occasionally when I start up the vehicle from a cold start, the fan will kick on for a few seconds and stop - it sounds exactly like this but constantly as I'm accelerating. I thought maybe it was due to the A/C, so I shut it off and it didn't change anything. When I first drove it today there wasn't any issues until about 5 or so minutes into the drive and things got warmed up... so I don't think it would be the fan clutch???

What is going on with this Explorer??????