Rough idle, 1988 RX no turbo.
 

Hey guys.

The car turns over and starts fine, but its a very rough idle at about 500-600 rpm.
After about a minute, it jumps to about 1500 rpm, then levels out at a good idle at 800rpm.
If the car has been sitting for a few days the problem is nuch more pronounced. .
I like to tinker, but I thought I might get some ideas of where the best things to look at would be
Any help would be great.

Thanks.
G.

BAC valve would be a good place to start. Do you still have the AWS?

Starting the car while touching the gas will interrupt/disable startup. I'm pretty sure starting it while in 1st also does this if I'm remembering this correctly.

Yes.
Could it be the Thermowax?

When the car is cold, and you turn it over, it should sit at about 2500 RPM until it warms up, and then drops down to about 800 RPM to idle.
The car doesnt do that anymore.
Its starts up but doesnt jump up until its warm and then drop down again.

A thermowax issue would cause a high idle to remain after warm-up.

The first thing that comes to mind is the BAC valve.

The second thing that comes to mind is the water thermosensor or air intake thermosensor. Check those connections. They're known to go bad. Sometimes the water thermosensor terminals push themselves out when you plug it back in.

Have you done anything under the hood lately in those areas?

I'd maybe save the thermosensor for last because it's the hardest to get to.

Edit: This could be a TPS issue too. Idle is tricky. There are many possible culprits. The trick is to work from easy to hard. The reason I bite my tongue about the TPS is that if you've never touched one before you might want to reconsider tinkering with it. It could lead you to a place you don't want to be lol. I'd argue that its the most enigmatic, cantankerous component on the car. I hate that thing.