If the car is idling weirdly and lower than normal the steering will get tighter as the power steering pump isn't being driven fast enough.
I have an after market ecu and for a long time the car would almost die as i came to a stop, or would actually stall at the lights, more so at night with the headlights on. Blamed my tune for ages and kept getting the tuner to retune the issue, wasn't getting charged for it. After a while he noticed that the tps voltage would intermittently "bounce around", at idle. Replaced the TPS and all fixed, idle is alot more stable too.
Have a look at your tps voltage, while the fault is occuring. See if it is changing by itself, without any throttle input. The sensor could be fine, but the throttle shaft, etc, could be loose/worn, causing false readings.
Could also be an ecu issue.