Hello
I have a 92 NA and it has recently developed a problem with its idle . When I put the throttle down and then let it fall it will fall to something like 500 rpm and then it will go back up to 1000 rpm this will happen at a stop light or when you come of the throttle . It will sometime stall the car as well . This has happened before but it sorted it self out .
Any help is appreciated
Have you disconnected the battery recently??
I had this problem and was able to sort it by following advice on here.
What worked for me was to start the car without touching the throttle and then simply leave it to idle for 15 minutes or so.
Apparently, it allows the learning ecu to set the idle at 800 rpm .
My car is much newer, so this may not apply - can’t do any harm though 
Hi, could be worth checking the PCV valve and cleaning it, it comes from top of the rocker cover, there a little ball in there which can stick, it’s a 10 minute job, and it cured my one with the same issue.
I’ll give that a go Cheers. 
Check the base idle, it involves bridging out the TEN and GND terminals in the diagnostic socket under the bonnet and adjusting the idle speed wit the air screw on the throttle body.
Cheers bud . I did this the other day and it looks like it has done it