I have a 1987 S4 Tii.

I have been chasing this weird idle issue where the car will idle at 1000rpm, and sometimes drop idle to 800-900. I noticed the BAC valve connector was broken, and the pins were not even making connections. I did a quick fix until I can get a new connector, gorilla tape. Started the car and everything ran normal, and the idle thing happened where it dropped to 800-900 rpm. I went for a drive (to get ice cream) and it worked fine, idled fine in the drive through, and did not overheat or anything. While I was turning my car stumbled (2nd gear, ~2k rpm), it sounded like it was running on one rotor, and vibrating. I pushed in the clutch, and it went away. Parked the car for a bit, and started normal and idled. When I went to leave, I decided to try and replicate it again, but going straight. I did it about 2000 rpm in 3rd gear, I also replicated it in 4th. I do not know if it happens at different rpms, but it feels like it happens at a certain throttle position, right before the pedal gets harder to press. I check the TPS using the ohm method a week ago and it was good. I do not know, if someone can share knowledge, that would be great, I am at a loss. If it is the tps, what can I replace it with?

Here is a different post of mine, the issues may be related.
https://www.rx7club.com/2nd-generati...luded-1157415/

 

I would start by checking for vacuum leaks. Especially with the turbo systems, you have different points in the intake that have varying pressures/vacuum at varying throttle states and positions. Before getting too carried away with the sensors just yet, check through the vacuum system and make sure it is in good condition and correctly routed.

 

I’ll hook up the smoke tester and see, I’m also going to build on of those pressure things to help. Any other thoughts are appreciated also!

 

there are also some points where the car is supposed to run on one rotor. the ecu wants the idle to be 750rpm, its not impossible that you are hitting some kind of decel fuel cut

 

you may be on to something, it feels like it happens when I slowly let off the throttle, then keep my foot at that spot

 

Well, checked for vacuum leaks with an evap smoke tester, found one by the turbo, and one by the brakes. Fixed them but it still does the same thing. I reset the TPS, and now the response of the car feels better. I think it may be some decel fuel cut, and mentioned before. I have also been able to recreate the problem consistently. It is right when I start pressing the throttle, right before it is leg go completely. It really only happens when I am decelerating, or just want to keep the car a consistent speed with very light throttle

 

Also, for some reason when cruise controlling down the interstate, my afrs went from bouncing at 14.7-15.6 to 10 solid. Idk if it’s a gauge issue or if I have some electrical gremlin going on. Ditch the RTeK and go megasquirt?