Gone through several past threads and found and tried some things. When decelerating for a stop while clutch is engage the rpm's drop to almost zero and engine starts to stall but then the rpm's return to normal idle. It only seems to do it while braking. Sometimes it does stall. If going down the road at 50 and just push in the clutch the rpm's drop to normal idle. Its almost as if the dash pot doesn't work sometimes. 12A 130kmiles. Carb rebuilt 5 months ago. New plugs 2months ago but not wires.Rats nest removed except for a/c solenoid. Replaced the dash pot.Took ignitors off and cleaned behind for the ground connection on the dizzy. Took apart and cleaned the clutch switch. Spring was ok. Checked and replaced the vacuum lines for brake booster at engine and booster. I replaced the slave cylinder 5 months ago and now clutch engages about half way up of pedal travel. It used to engage just a few inches off the floor.I've noticed sometimes when engaging clutch to start car, starter grinds occassionally so maybe the clutch isn't adjusted properly? Thanks for the help.

 

Possible vacuum leak inside the brake booster. If pressing the brake while sitting still does it, that's a almost-for-certain.

You can try capping the brake vac line for verification. Also check the one-way valve in the brake line.

 

Keep in mind not all bcars have booster line check valves. My car does exactly as you've described.

Starter grinding is the starter to flywheel mating. Nothing to do with the clutch.

Make sure the idle is set right, mixture is set right, and no vacuum leaks.

You can cap the brake booster line. Pinch it shut while it's still connected to the booster and see if the rpms change. If you've tuned the idle mixture around a booster vacuum leak, you'll have to adjust it again once you've replaced the booster.

The best way to tell is find someone with a vacuum pump gauge. I checked mine and it would only hold 15inhg which is lower than the car idles at. Then if I pushed and held the brake, it wouldn't hold vacuum at all. Huge vacuum leak. Waiting for a few extra bones to replace mine.

I can press the brake 3 times quickly at a stand still idle, and the rpms will drop to 400 or kill the engine entirely.

 

Does anyone know a place to get a check valve, my '84 GS has this issue and no check vlave stock, and the pull and picks around here don't carry many 7's lol.

 

want ad in the for sale section on this site.

 

Thanks

 

I just tried it tonight. Tonight after returning from a 20 min drive. sta in driveway with emergency brake on in neutral. When I pressed the brake pedal the rpm's would drop like 200-250rpm. I would let the rpm's return to normal idle,press the brake pedal and the rpm's would just slightly drop 200-250. So it looks like that is the culprit? Do all FB use the same booster. I can get one from an '81 but really don't want to do this repair twice.Know what I mean? Thanks for the help.

 

Look up a parts house part number for the years or check mazdatrix. See if they interchange.

I'd say that's the culprit.

As for the check valve, I was always told it was for oil control as typically it's under vacuum there's no problem, but go WOT with no vacuum and oil can find it's way there. Mine went 274,000miles. I think no check valve is okay.

 

Ever come up with anything on this?

Weather turned colder, and mine is doing it really bad now no matter the idle mixture or idle speed setting.

WB shows the engine goes WAY lean 17-20:1 AFR as it stumbles and the rpms drop to near zero.

Happens the same as you describe.... when coasting with the clutch engaged..... and pushing the clutch in just before stopping.

 

All cars should have a check valve between the booster and vacuum source. Otherwise, no vacuum will be "stored" in the booster ready for use. Instead, it will try to draw straight from the motor while it is idling down, causing stalls.

However, having said that, a bad check valve condition is usually also accompanied by a hard pedal. Therefore, I believe that you have a torn diaphragm in the booster (but I would still start with the check valve due to simplicity compared with a booster swap).

For proper installation of the check valve, it should be able to draw air from the motor to the booster, but not from the booster to the motor.




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Anyone have a part number for such a check valve?


Both my '82 GSL, and '84 GSL-SE parts car, had no check valve inline. Booster in the '82 is new from Rock Auto. Master is new also, which caused the old one to die.