I have a pretty big crack in the downpipe after where it meets the flange right off the back of the turbo and right before the O2 sensor. Do you think this would have anything to do with the idle situation I've been chasing forever...???

 

You should fix it and see.

 

really depends how large it is, yes a large leak can cause an idle issue though.

 

I fixed DP crack (was pretty big) w a nice reweld and it didn't fix the idle issue.

This idle issue is driving me crazzzy now for awhile. It idles perfect for a few minutes and then all of the sudden stumbles really low (almost to a stall) and then catches itself and comes back to perfect idle for a moment then stumbles again, then catches itself... Usually repeats 3-4 stumbles before ideling steady again for a good minute + before it does the stumble dance all over again....??

 

vacuum leak

you also have a variable resistor

 

So I messed w the variable resistor after doing some searching. Jumped out the coupler and turned resistor towards "L" until it stumbled then backed it off towards "R" a quarter turn and it idles nicely. Checked timing w the coupler still jumped and both marks were dead on. She still stumbles after coming off throttle almost to where it feels like it's going to stall and then she catches and returns to a good idle.

I have a friend w a snap-on smoke machine. Going to check everything out this weekend in regards to vacuum leak.

 

I've seen this happen with secondary throttle plates sticking a bit. I've seen it twice now.

 

You should put a flex pipe so it doesnt crack again.

 

Don't happen to have an atmospheric bov do you? Stalling after coming of throttle sounds like that.

 

Nope. It still has the stock recirculating valve.

The motor is a S5 w a streetport in a 87 TurboII everything else. 3" exhaust (no cats) and a HKS piggyback computer. It's old school from early 90's & plugs inline btwn the harness and computer.

I googled "RX7 HKS piggyback" and everything that comes up looks nothing like what I have. I'm going to pull the carpet to check it out again, haven't been under there in over 3+ years.

 

I used the machine on a Land Rover this morning and smoke came out all kinds of places....!!! I put it on the RX & nothing....??? First time using this thing.

 

How often does the idle issue happen? If you tap the gas does it return to normal idle? Or if you push on the throttle plates?

 

Before it was dancing btwn 1200 and 500 once it got warm.

After adjusting the TPS, variable resistor and making sure timing was DEAD on it has changed to...

After giving throttle it drops down to say 200 rpm or near stall and then something picks it back up to a perfect idle on it's own....??

 

Maybe this: https://www.rx7club.com/2nd-generati...etness-785082/

12th paragraph down, 1st post....?? Off to check out alternator.

 

Today cold start is gone for first time ever. No perfect idle @ ALL. Just 1700 for a 3, 4 seconds and STALL.

Didn't even bother checking voltage.

 

1700 is low for AWS, sounds like your idle is set too low and i still believe you have vacuum leaks.

 

the HKS F-con we got worked pretty well for what it is. as you know it goes between the ecu and the injectors, so it can just modify fuel.

the F-con has since received many many updates and changes since, the newer ones; F-con V Pro, is supposed to be the best rotary ecu out there, although there is no english version. it still works like the old one, so you can use it as a piggyback, or it can be a full stand alone. if you look closely this gives (gave?) the JDM tuners a lot more flexibility than we have here. for instance, they can have a fully tunable ecu, but add the FD CAS, ignition*, upper intake/tps/ait, and subtract the AFM, without having to totally rewire the whole car.


*the FD ignition coils are less powerful, but are also less prone to crossfires, smaller and lighter

 

Ahhhh yes. A google search of "HKS F-Con" now shows the one I have.

I haven't had the time to play w the car some more since I was off last week.

I'm at the point of re-adjusting the variable resistor bc at least before I touched it (and it was the ONLY thing I touched) the cold start worked and it at least stayed running.

 

What an idiot I am...!!! I never put the vacuum hose back on the intake from pressure sensor after smoke test. Volts are 14.4 @ 1100 cold start idle. She dropped down to 900 and held there w out a bounce @ 14.1 volts. After a year of bouncy idle I'm SUPER happy w that for now.

What's next drop her to 800 by use of throttle stop screw...??

Edit: So sitting still from a dead COLD start all is fine. After a small drive she's still coming to either a full stall or a near stall before it kicks back up to 800-900 when letting off the throttle / load.....???

If it is a vacuum leak like you think Evolution I'm READY to pull EVERYTHING and reseal / regasket it ALL.

 

if you want to reseal it that is a good idea for a car with 30 year old gaskets and injector seals, if you want to bypass it for now you can turn up the BAC idle screw to a higher idle and adjust the variable resistor until the best results show.

 

The motor was swapped out for a S5 block w a streetport about 5 years ago so everything's not too old. 3" straight pipe off the turbo to Y pipe then 2.50's out to dualie Flow Masters, no cats or presilencer. I'm wondering if poor back pressure has anything to do w deceleration stalling....?

This BAC has no screw....??

 

So I finally fixed the idle issue. One big circle jerk was needed to be done. Adjust variable resistor, TPS, throttle stop screw... Full circle three times did the trick.