Hi Folks,
I posted about this issue as a comment on one of my other threads but at this point I've done heaps of diagnostics and parts replacing with no results so I figured I'd make a new thread to pinpoint the exact cause.

The issue is my car likes to stall out when I let off the throttle from 3-4k with the AC on. It can just barely manage to keep itself alive with no AC on but with the AC on it chokes itself out.

I'm running stock ECU with a bone stock engine except for the secondary throttle being deleted. The car idles happily at around 750rpm no AC and about 950 with AC.

I have tried:

• Dashpot replacement - got an OEM replacement from ray crowe -- no luck. It's set to start damping the throttle at 2800 rpm
• Un-kinking a moderately kinked AC line going into the dryer. I definitely expanded the size of the restriction after clamping on the tube a bit but it didn't really have much effect.
• Cleaned and tested my idle air control valve.
• TPS Adjustment: My TPS was barely out of spec (about + .15v on the upper wire. bottom wire was in spec.) Now it's in spec but no luck
• adjusting the air bleed screw on the bottom of the throttle body in both directions. Adjusting the screw CW or CCW didn't seem to have any impact on the car being able to stay idling after letting off throttle
• Bufferfly adjustment screw -- I tried using this to bring the idle high enough to keep the car from stalling but I had to bring it all the way to 1500rpm idle to get it not to stall. Definitely seems abnormal

The car when hot pulls anywhere between 13-17 inHg vacuum at idle according to my cheap gauge. It's a brand new engine with about 100 miles on it.

 

Open manual idle bypass.

It's probably one of or a combination of both, especially being your summer, tired turbos throwing oil into the intake, which both cakes throttle and bypass restricting glow, flashes in the heat, taking up volume. Mine is doing similar, with bonus compromised water seal eating a small volume of coolant, which can also stall you.

 

Did you follow the idle set procedure in the service manual? You have to put it into an idle set mode, by jumpering TEN and GND in the diagnostic box under the hood. That sets a fixed ISC valve duty and fixed spark timing.

Are you sure there isn't an air leak in the system? Old split hoses, leaky gasket, etc

 

It has been some time since I’ve played with the stock ecu. If you have a bone stock car, including the air box and you’re sure you don’t have something simple like a clogged air filter, bad clutch switch or a vacuum leak. I would count how many turns out the air bleed screw is from full closed and check your throttle body primary butterfly opening angle. You will read in a lot of post to set the air bleed screw out 1/2 turn from closed but this is only for the power fc. In the factory format it’s out around five to six turns or more if I remember correctly. This allows the duty on the ISC to be within a range to act as a Electronic dashpot that the factor ECU controls. If this is outside its range it will not have enough adjustability to catch the engine as it falls. If you read the fms page F-81 it does go over this. Also check out F-133 & 134. I’m not sure if the factory ECU has a relearn feature or not ( May be disconnected the battery for a period of time will reset it back to baseline), but the mechanical settings have to be correct first. With diagnostic box jumped and the timing locked ( fms F-17 ) You should have a base idle of around 700-750. Chances are you’re just out of adjustment and the factory ECU has compensated for or it. Surprisingly enough to factory ECU is pretty forgiving.


~ GW

 

I tried smoke testing and couldn't see smoke coming out anywhere. I'll try doing the FSM idle set procedure, haven't done that yet.

 

I think my bleed screw is about 4 turns out. Less or more seems to make it more prone to stalling. Thanks for the info, will try setting the idle one more time.

 

Few things -

- Clean the ISC. A dirty and sticking ISC will do all sorts of weird crap.
- How does the car drive with the AC on? Do you "feel" the AC being on? Does it feel like it's bogged down or lower on power? If so it's something with the AC side of things, like too much refrigerant, compressor is tired, or too much compressor oil. The FD when running right with a healthy AC system shouldn't have any noticeable drag or bogging with the AC on, it should drive just as good with it on as off.
- Does the car just have the revs drop straight to zero or does it hang at, say, 500 rpm then stumble and die? Does it seem like the dash pot is "catching" the idle?

Dale

 

ISC is sparkling clean and works good.
The AC blows ice cold right away. I'm still in break in so while keeping it under 3000 rpms it's hard to tell how bogged down it is.
I'm able to drive it and I don't notice it being any harder than with the AC off other than it stalling out sometimes if I forget to keep the car alive by backing off rpms real slow.
The revs drop straight to zero it's pretty much not able to catch at all with AC on. With AC off it'll kind of stumble at 500ish and then come back to life.

 

what model year and which AC system is it?

 

92 RHD Type R with the Nippon Denso unit.

 

Performed the FSM Idle set procedure. issue persists but I was able to get an idle where the car mostly doesn't shut off. It still stutters a bit when letting off with AC on.
Idle bypass screw is about 2.5 turns loose.
Indicated idle RPM on the tach with AC on (not 100% sure if it's accurate) is 1050 RPM.. so a bit higher than it's supposed to be.

If I completely let throttle off in neutral at 4000rpm i can get it to stall itself out but this isn't a common occurrence in daily driving. In short: it's drivable but it's idling high.

If anyone has any other things to try out I'm all ears.

Also temps in heavy traffic today peaked at 206 water temp, 228 oil temp with mineral (break-in) castrol 20w50 oil. It was 89F here at the time of driving.
Normal temps for the high idle?

 

you've probably got a lot of electrical load on the engine due to the fans. are you sure your electrical load detector is working?

 

Thinking about it, I remember you had some tuned JDM ECU in your car when you got it, correct? Is that ECU still in the car? What ECU is in the car?

If you have a US ECU that would do weird stuff with idle.

Dale

 

I bought a used fd stock ecu off ebay, most likely a us ecu..
I have an apexi pfc ready to go in but haven't had enough break in miles yet to bring it to a tuner to get it set up. Maybe I'll just put it back on the tuned JDM ecu...

Drove it to work in some serious traffic today and temps peaked at 225 water 245 oil. Slightly concerning.. might also be having some issues with one or more of the fan speed relay inputs activating. Gonna try jumping the fan diagnostic pins to see if it helps bring temps down during my drive home

 

I haven't actually thought about this but it would make sense since I have a lot of aftermarket electronics. Radio, LED headlight kit, wink mod control module..but I installed an aftermarket "150amp" alternator and I figured it would be able to handle the extra electrical load.

 

If you have a US ECU, there's your problem.

JDM ECU's have more inputs going into the ECU. For the US market they had to move those to a separate box (the ELD computer) since the US ECU has more emissions stuff.

Just put the PowerFC on. You DO NOT have to cut wires since you are on a JDM car, just plug in. Read the FAQ on doing the idle learn.

Stock PFC map is basically the stock ECU map with a few tweaks - you'll be fine.

Dale

 

edit: nevermind a quick search yield the answer
​​​​​​
I bought a used one. Is there a reset procedure to get the original pfc base map?

 

http://www.banzai-racing.com/store_i...owerFC_FAQ.pdf

Dale

 

Thanks again dale!!

 

Raymond wrote this thread some years back. It will help when you install the power fc.

https://www.rx7club.com/3rd-generati...needed-841706/


~ GW

 

ah, the old bone stock engine connected to a bunch of not bone stock stuff...

 

I'm an idiot. I completely forgot where I got the ECU from. It came from a friend who took it off his 93 RHD touring-- so there's no possibility I'm running a USDM ecu on a JDM car..
Mine is a 92 RHD type R. Not sure if there are any major differences in ECU between the two.
Still haven't put the Apexi PFC in but things just got a bit more confusing..
Gonna put it in tomorrow.. will post results.

 

Power FC's aren't known for idling great out of the box. I mean I wrote a bunch of stuff about it. Just dropping a Power FC in without tuning solves some issues and creates others, just to warn you.