This is the first time ive had this problem after owning 3 privious rx7s. i bought a 88gtu without an engine and had a rusted out 86 rx7 with a rebuilt engine with 8000 miles on it. the engine has great compression and ran awesom in the parts car. i noticed it hunted for idle a few times and would go away. After swapping the engine and fuel tank in my 88 and removing the emissions it revs to 3000 for the warm up cycle and then constantly bounces between 1000 and 1500. ive checked everything with an electrical tester and everything checked out fine compairing it to a haynes manual. injectors omed fine. tryed 2 map sensors both of wich were fine. i had 5 tps sensors laying around tried each of them and adjusted them. throttle plates ajusted. brand new fpr. bac checked out good acv was good. ive run the car with both of these eliminated with the same effect. there are no vacume leaks. tried 4 of my ecus. cleaned all grounds. the only thing i havent done is replaced the fuel pump and i will be doing that shortly. any ideas on whats going on?

 

what emissions did you remove?
and it could possibly be a small leak in the air intake

 

No idea. i have a problem similar. i have a 86 non turbo and it wont start now either. i put a after market intake on now it wont start. it starts blows alot of whit the shuts off after 20 seconds. any one ideas??

 

i had a similar problem when i took my 91 and put a 86 motor that ran good out of a rust bucket changed and tps and bac it went away. what electronics are you using? the 86 and most of 87 have different electronics

 

its all 86 electronics and i dont believe any of the s4 cars have different electronics. the differences start between s4 and s5. s5 cars were 89 and newer. i removed the rats nest acv egr valve. i also tried running the car without the bac and i still had the same problem

 

the 86 and part of 87 run low inpedence injectors ecu and have a ballast/resistor under the air box. so you are running an 86 engine harness?

 

hmm i had thought that the difference in low and high imp injectors came between s4 and s5 cars but i really dont know for sure. yes i am running the 86 wire harness and ecu. along with 86 maf

 

I'm having a similar issue. stock '87 FC NA 5sp. Replaced the TPS and adjusted to 1k ohms w/ engine warmed (20+ min @ idle) Engine starts like a champ, hits high idle of about 2k, hunts all over the place for mid idle (1k - 1k8) finally tries to settle on low idle and swings from 300 - 1k eventually stalling. In order to hold idle I have to barely keep a foot on the gas. I can immediately restart the car, thus I don't suspect injector flooding. I'm fearing an ECU replacement (due to cost), but am wondering if the BAC could cause this? It shouldn't hurt too much to pull it and clean it.