Having strange idle issues

I have a 2003 toyota corolla

I recently had a block heater installed. I picked up the car and when i got home and put it in park the car was idling at 1200 rpms in park fully warmed up. It’s always idled at 750. Since then I’ve had a couple other problems too. When i cold start the car in the morning, it used to warm up at 1800 rpms for a couple’s minutes until it started to lower. Now itll sit at 2000 then slowly work its way to 2500 before it starts to slowly idle back down to normal. When i sit at a stoplight in drive for a couple minutes the rpms will drop to 500 for just a second then return to normal.

These problems started immediately after the block heater installation. Ive cleaned the maf sensor, the throttle body spotless, replaced the IAC valve and have checked for

vacuum leaks. Im not sure what else i can check at this point. Could something have happened during the installation to cause these problems. Any suggestions would be greatly appreciated thank you