cruise throttle surge

[1995 toad]

one can even drive all week with the DLC Diag jumper in place, and see 12  all week and then on moment bam , new code pops.
cold idle can be 1000 to 1500 rpm colder the block that faster.
hot is 800 with all accessories off.  (means no AC on this car)
many things cause failed idle regulation.
coolant not hot, 180f.
TPS idle switch not closed, and at 0vdc.  if 5vdc idle is cancelled.
air leaks. (aka vacuum leaks from anywhere to the plenum)]
ECU in limp home mode.  not 12, means that , mostly.
if way below 800 even 400 , egr main valve  leaking like mad.
leaking injector or clogged, may cause low idle speeds. below 800 hot.
misfiring engine, blew 800.
1000 hot, no AC turned on is ISC is off line or stuck open.
or engine super rich and huge vacuum leaks at the same time.
The ECU wants to control idle at 800 hot and aggressively modulates the ISC valve to do that.  we see it can do that. only why remains.

Idle was stable today when cold started missing through warm up idle stayed fine once warm sounds like it is the egr from what you have explained. What does the vacume line do that comes from a valve at the front of the intake and goes through a vacuum  dashpot and is hooked to the egr with the same hose... will clean the egr and se what happens

I replaced the egr and it has been running ok. the nag light came on at 170000 miles cured that... after about 75 miles of driving on the way home today the cel came on today... no issues the rest of the way home. so I pulled the codes and it says 51 egr failure.. ?? checked all the connections...