Drop in RPM's

2000 Mercury Sable Wagon, 3.1 engine auto transmission, 133,000 miles. Last week I removed the negative cable from the battery in order to change the starter motor. Imediately after changing the starter I took the vehicle on a 800 mile trip. while on the highway, I noticed that while traveling at highway speeds, if I took my foot of off the accelerator, the rpm’s would drop off by 200-300 after a brief delay. Even if going down hill, the rpm’s would drop off and the vehicle would slow down. Once I put my foot back on accelerator, just barely touching it, the rpm’s would jump back up the 200-300 that it had lost. Once I got off of the highway and would come to a stop with foot off of the accelerator, again after about 10 seconds, the rpm’s would go from the idle rpm of 800 down to around 500 and would start to misfire and eventually stall. The vehicle would start right back up and if I kept my foot on the accelerator, it would be ok. The check engine light did finally come on after stalling with codes for “random misfire” and “fuel mixture lean bank #2”. I checked for a vacuum leak but did not see/hear anything obvious. Has anyone experienced this before???

When disconnecting a battery on a vehicle the computer loses it’s adaptive memory. This means the computer must relearn all the operating parameters under all driving conditions before te vehicle will run correctly. You can read about is here:http://www.aa1car.com/library/battery_disconnect_problems.htm

So maybe all that’s required is to drive the vehicle under various driving conditions or what are called drive cycles so the computer is able to relearn the adaptive memory.


Thank you tester,
I have driven the car over 1000 miles and two days. Not very many start and stop cylcles though. Maybe I will drive it for a few more days and see whats happens. Thanks again…

In particular it sounds like it might need to relearn idle air control valve operations.

If it doesn’t get back to normal after a few more drive cycles I would clean the IAC.

I was looking at that last night, it looked a little dirty, that will be my next move, thank you.