01 Malibu clunking hard in to drive and shifting hard?

My 01 Malibu just started banging very hard in to drive and then when driven it shifts very hard in to 2nd and 3rd gears. My check engine light came on and the code read out "IAT sensor" I replaced it and there was no difference. I also replaced the MAF sensor and TPS sensor because I had those two sensors fail before on different cars and the transmission started to shift erraticly. Any ideas on any other sensors that could cause this hard, banging shifting? My research on the internet suggests that this is a "limp mode" or "fail safe" mode the computer puts the trans in when the computer gets bad information from a sensor.
Thanks for any input?

did you check the fluid level?

did you check the fluid level?

No dipstick on the 01 Malibu, just a plug you can remove on the side of the trans while the motor is running and make sure the trans oil is just up to the threads. I just had a trans oil and filter change about 2k miles ago, watched the mechanic check the level.

Problem solved: It was the connector on the IAT sensor, I repalced the whole plug assembly and the trans shifts great now and everything is back to normal. I received the information about the connector after I replaced the IAT sensor which came up as bad on a code scan. I will never just change a sensor again without checking the plug and wire connections to the plug.

i think this is my prob too. i just posted it and failed to mention the check engine light because everyone keeps telling me that it has nothing to do with my prob. if its not too much of a prob could some one please explain this better for me. i'm kinda lost in the replies. i'm a college age girl that has no clue when it comes to cars.

The IAT sensor was also my problem. It's more often the wires going to the sensor than the sensor itself. If you look on the tube between the air cleaner and the throttle body, it's the one on the side pointing towards the back of the car with two wires (black and purple i think) coming out of it. Carefully pull the connector off the sensor and stick a voltmeter on it. It should read 5 volts with the key in the "on" position. If it does, try replacing the sensor for $12.

If it doesn't, wiggle the connector around a little until it does. The dealer sells a replacement connector with two butt connectors and about a foot and a half of wire on it for $20, or you can go to 47 junkyards at $2 each until you find a good one. Splice it in there and plug it back in.

I wonder how many times a dealer has replaced a transmission, noticed the continued problem, and replaced the wire. I bet they never tell the customer, but I'm sure they charge them for the replacement connector.

I am experiencing the same problem with the "clunking" but have not gotten any CEL (light).

I am willing to change the sensor or connector but does anyone know why an Intake Air Temp sensor would cause the transmission to shift hard?

I didn't get the CEL light for a few days, when I did I just changed the sensor first. The plug in harness was the culprit! Harness/Plug assembly is $20.00 from the dealer, IAT sensor was $12.00 from Advance Auto. I don't know why the IAT sensor causes the Trans to clunk in to gear & shift hard, but it does!

ok , you get a bad shift from the iat sensor because it changes the fuel to air ratio, giving the engine a different amount of torque. the alvebody in the tranny shifts when the engine hits two parameters, rpm,and torque,thats how it knows not to shift when your flooring it on an on ramp. i think the different amount of torque causes the irratic shift.

Well I did replace the AIT sensor and the car still clunks when I put it in gear from Park.

Other than the initial shift from Park it seems to shift OK

Does anyone know why it makes that clunk form Park?

Well I did replace the AIT sensor and the car still clunks when I put it in gear from Park.

Other than the initial shift from Park it seems to shift OK

Does anyone know why it makes that clunk form Park?

I think its normal for it to do that if you just started the car cold. Until the engine reaches a certain temperature, the computer will idle it a little faster, about 1000-1100 rpms I've noticed, and shifting into drive with the engine running at a faster speed may cause this. See if it clunks into drive as harshly once the ingine is warmed up.

I'm not sure how much the IAT has to do with the initial shift from park to drive.