seamusmurrin17

Searching shows plenty of folks claiming this problem but no one sorting it out. Symptom is stall when cold coming to a stop. Or, rev the engine and it when rpms drop it doesn't recover to idle and stalls. Mine, when hot under similar stop/rev conditions will lumber below 500rpm for a few seconds and slowly recover to normal idle.

Mine is a '85 GSL-SE (ie fuel injected).

I have been through the excellent "Rx-7 SE idle problems" write up once. But can't seem to figure this one out. Or, I missed something following the troubleshooting guides.

Any tips?

djs2571

It should be the bypass air control (BAC) valve. Located on the left of the car on a rubber hose coming out towards the rear of the intake chamber (the one with GSL-SE on it).
Verify that it is working properly by turning on and off the AC, and adjusting it, you should be able to get it to rev up and down with the adjuster screw.
It could also be the throttle plates are closing too far, so the BAC is compensating to give you normal idle, when it should only be needed to adjust for additional load - like with the AC.

With the BAC electrical connector unplugged the car should idle fine, if not there's a throttle positioning problem.
I recall adding a restrictor inline with the BAC, basically a neck down to a 1/4 hole in the tube for the BAC connection, though I don't recall if that was to fix this problem or something else.

Another thing is the dash pot, if it's out of adjustment the throttle will close too fast and cause a similar issue.

It could be the TPS, though that didn't make any difference on my car. Or the fuel injectors leaking a lot, may cause a minor flood when the engine is 'coasting' back to idle.

PM me or something if you'd like to go over anything more specifically.

thunkrd

iTrader: (1)

could also clean tb, make sure no leaks

btw it says RE-EGI on it not gsl se... but its ok

LongDuck

Djs is on the right track; vacuum leak or Cold Start Assist (*not the Sub-Zero system), or possibly a coil/ignition issue. Keep reading...

The SE's have a unique method of operating the fuel injection system, and on cold start, you have an engine that is 'tight' internally, an electronic ignition system (igniters/coils) that aren't up to temperature, and some air controllers that interact to create some strange fluctuations depending on conditions. Let's start by breaking these down individually;

1) BACV - The Bypass Air Control Valve is used to up the idle when you increase load on the engine, such as running the A/C compressor. Whenever the engine rpm drops, the BACV job is to see the drop, increase airflow to the Dynamic Chamber (the "RE-EGI" box on top), and allow the engine to recover from the rpm drop. These are simply air valves that let air in (behind the Air Flow Meter) to the intake to keep the engine running at around 800-900 rpm. If your idle is below that to start with, that could be part of the problem. Idle speed is set using the turnscrew mounted to the Primary Butterfly Throttle Rod, NOT by using the turnscrew on top of the air inlet at the Throttle Body - get the idle set to 800-900 rpm, and then see if it still happens.

2) Thermowax Pellet - At the rear of the Throttle Body (near the firewall) is a green plastic extension that receives water from the back of the waterpump and returns it to the top of the block. The TWP is heated by the hot coolant when the engine warms up and when it melts, it allows a spring inside of it to operate against the Throttle plates (i.e., choke plates) in front of the Secondaries, and also opens up vacuum airflow to the diaphragm valve located near the front of the TB - opposite site of the TWP. This has the effect of allowing the car to see air choke with cold coolant, but once warmed up, the plates are opened by the vacuum diaphragm valve to allow unrestricted airflow to the engine. The TWP cam is 'set' during cold start by the SE owner pressing ONCE on the gas pedal (which sets the cam against the throttle rod), all the way to the floor, and then releasing it, then cranking. In other words, don't 'gas' the pedal on cold starts - it doesn't help the engine to start. Make sure your coolant lines leading to the Throttle Body are clear and passing coolant, or the TWP won't work correctly (and will keep the Secondary throttle plates choked all the time - not good on fuel economy or power output at ANY temperature).

3) Dashpot - The Dashpot keeps the throttles from closing quickly and snapping shut with the force of the return springs on the Butterflies. It's located toward the firewall, and you can test it by pressing down on it with your thumb and timing how long it takes to come back up. If you push it down all the way, it should take about 5 seconds to come up again, slowly and evenly. If it snaps to the top, then that's likely your problem. Suddenly stopping the airflow to the engine will shut down the AFM, turn off fuel, and the engine will die immediately. Dashpots are cheap, easy to replace, and a simple fix.

4) Cold Start Assist (secondary throttle plates) - As mentioned above, the Secondary Throttle plates act as chokes on the primary air flow. With the engine warmed up, you should be able to remove the big air pipe leading to the TB, and see that the plates are nearly horizontal (fully open). If they're closed at all with a warm engine, you need to find out why. There is a vacuum chamber toward the front of the engine that controls these choke plates, and if that has a leak, you may not be getting them open or they may be stuck open - either of which will contribute to cold start problems.

5) Ignition - Changed your cap and rotor recently? Whenever things start to get cold in the winter (and also when cars come out of hiding during the spring), there's a rash of people posting here with starting issues, usually traced to a cracked cap or rotor, which prevents the engine from firing. This doesn't sound like you, but is cheap insurance...

6) Long Shot - Vacuum leak - With a FI car, any air that manages to get into the engine without 'registering' at the AFM will result in all kinds of wierd problems - lean mixtures, 'hunting' idle, idle surge (search on that for more), and other problems can sometimes be traced back to vacuum leaks. There are MILES of vacuum tubing in an SE engine bay, and don't overlook the ones that are under the RE-EGI box that power the BACV vacuum solenoids, and also those which provide air to the oil injectors. Any vacuum line should be checked under there, including removal of the Upper Intake Manifold if you have the time and inclination - and nothing I've listed above has fixed the problem. Extra air getting in would allow the BACV to be irrelevant to manage idle speed, and that air source could be allowing enough bypass air to come in that the AFM isn't needed, stops registering airflow, and shuts down fuel injection. (*if you didn't know, the fuel is only injected when the AFM shows air coming in, and air only comes in when the engine is turning/cranking)

That should give you a good start. From the symptoms you described, it sounds to me like one of the TB components that's not working correctly, so focus efforts there. Good luck,

seamusmurrin17

Thanks for these really helpful posts. I am trying to work through this methodically.

First, the idle was not right. The screw at the butterfly took care of that (I had missed this adjustment screw before) and now I have linear response back at the air adjust screw. I set the idle at 800.

Next, ignition timing. It was off. Not by much but both leading and trailing were off. It already seems better when hot. Will have to see if it helps when cold.

The dashpot, based on the test above, is shutting very quickly. I don't see it listed at Black Dragon. Where can I find one?

djs2571

If the timing is off, do check the cap & rotor, I had to replace mine yearly because the contacts would start corroding. If you look under that rotor, there's a cover plate and I think this still had a small weight set for moving the timing a bit - which could easily mess with the timing. In any case, make sure that section of the ignition is all clean and working properly.

sorry about the gsl-se / re-egi mixup, I haven't had the 7 for a few years.

I'd suggest finding the dash pot at a junk yard, I think the 2nd gen used the same size and everything. I think the test isn't that it pops up slowly, but that it provides some dampening when it's pressed down... to provide a soft stop of sorts to the throttle plates.
Mazdatrix.com has PN 13-2150-8341 CARB DASH POT RX7 81-85 $ 90.00 I assume it would be the same for carb and the fuel injected but i'm not sure. far cheaper to go to the junkyard.

Glad you're on a path of improvement with how it runs.