Dear Car Talk:
I have a 2001 Ford E250 van with a 5.4-liter motor. When you step on the gas and then let your foot off the pedal, the throttle drops very slowly. I've replaced the EGR, the throttle position sensor and the idle air-control valve, and I've cleaned the throttle body. I don't know what's wrong or how to fix it. Can you help?
I don't think so, Skip. You've tried most of the things I would have suggested.
Let's assume you did all of that stuff correctly, and that you didn't notice any scoring or wear and tear inside the throttle body that could cause the butterfly valve to get hung up. The next thing I'd look for would be something even more simple that got overlooked, like a sticky throttle cable.
You can check that by disconnecting the throttle cable from the throttle itself, and then operating the throttle by hand with the engine cover off. If the van returns to idle normally without the throttle cable connected, then you know it's the cable, and you can replace it.
If it's not that, the next thing I would hope for is a good, old-fashioned engine fire. You'd be surprised how many mechanical problems an engine fire can solve, Skip. Good luck.