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RPM drops above 45 mph

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guyute85

New member
Hey everyone, long time searcher of this site, first time poster.
I have an issue with my '02 GT. When I'm coasting along at anything above 45 mph, I get a sudden drop on my tach down to around 1000, and it seems to bog the car down. It doesn't happen when I'm giving the car gas, and it doesn't happen when the check engine light is off. The engine light has been on for about 3 months, and then shut off again after I replaced the thermostat, but now it's back on again. I'm not sure what it would be. I checked out the MAFS, and it seems to be working fine. Anyone have any input into what this could be? Thanks!
 


guyute85 said:
Hey everyone, long time searcher of this site, first time poster.
I have an issue with my '02 GT. When I'm coasting along at anything above 45 mph, I get a sudden drop on my tach down to around 1000, and it seems to bog the car down. It doesn't happen when I'm giving the car gas, and it doesn't happen when the check engine light is off. The engine light has been on for about 3 months, and then shut off again after I replaced the thermostat, but now it's back on again. I'm not sure what it would be. I checked out the MAFS, and it seems to be working fine. Anyone have any input into what this could be? Thanks!
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get the car scanned and find out what the code is, auto zone will scan your car for free.
 
You do realize that the trans. shifts into OD around 45, right? Probably why the rpm's drop. Try leaving the shifter in "3" instead of "D" and drive at 45 and see if the rpms drop. If they don't then shift it into "D" and see what it reads.

And yea, get the codes scanned. We're not good at guessing games for CEL's, lol...
 
mine did that, could be a vacuume leak. i turned the idle up a little via screw on the throttle body, until i get the new fittings.
 
That's a Mass Air sensor code. Try replacing it with a junk yard sensor.

As for the RPM drop. Most likely just the Torque convertor lock-up. Completely normal and improves mpg. Guessing if you tap the brakes or give it light throttle it pops back up?
 


The Mass Air sensor should be fine. I unplugged it and took it out and cleaned it off. The RPM drop only happens after about 43mph and when I'm not accelerating. It happens when I brake and coast, and it only lasts for about a half a second, but it will do it multiple times until either I give the car gas, or I go under 43mph.
 
RPM drop is the TC locking and unlocking. When you let off the gas in 4th gear the car stops adding fuel and spark to help with fuel economy.....Touching the brake the TC unlocks. Giving it gas after touching the brake it stays unlocked for maybe 3 sec then locks
 
I also concur it is the TC locking up at ~50 mph. The TC lockup is to improve gas mileage, which you should notice on a flat land or down hill. If you slightly press on the brakes it will disengage and RPM shall rise.
 
guyute85 said:
The Mass Air sensor should be fine. I unplugged it and took it out and cleaned it off.
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If the MAF sensor has gone bad, you can clean it off as much as you like, but it's not going to help. It needs to be replaced altogether.

As for the other issue, I agree with everyone else that it sounds like the torque converter is just doing its job.
 
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