cammil

I have a 1985 GSL-SE 97k miles all original. On the freeway this morning I notice that when I back off the car slows down real fast (from 80 mph).... Don't think too much of it (surges sometimes....). I get on the offramp, push in the clutch to change gears and the motor stops......

Still doing 50 mph so I complete the gear change and the motor starts again. Still make good power over 3000 rpm, no noticeable smoke but as soon as the rpm drops under 3000 motor stops dead unless you pump the gas.

So I limp it to work and now I'm trying to work out what's wrong. (No tools with me of course.) It will start but throws a lot of smoke at low rpm. Still seems to run fine at higher rpm.

jeremy

iTrader: (1)

sounds like its running rich at idle and killing itself. injectors not closing properly? thats all i have. my other guess would be an emissions device is screwed up. that seems to always be a problem. not sure if that would be enough to kill it idling.

WackyRotary

Sounds like a Huge vaccum leak to me.

FJ

If the smoke is very black, it sounds like the air flow meter flap stuck open. (The smoke was black?)
It would be less noticeable at higher RPM as the flap would be open then. At, or near, idle, the stuck flap is telling the ECU that a large amount of air is flowing so it will add a lot of fuel. It will stall at idle and run off idle, but extremely rich (black smoke), as jeremy mentioned.
If you remove the air filter (engine off) you will be able to see the flap and if it's closed. A small amount of dirt that gets past the air filter is all it takes to jam it open.

Other than that, the only thing I can think of is a sticky linkage, causing the throttle plates to stick open. Again, it would run well at higher rpm, but would die at idle, this time because of too much air. But you wouldn't get smoke if the plates were sticking.

The smoke is important: if it's not unusual for your car to have blue smoke, I would go with WackyRotary and suggest a major vacuum leak. (The large line on the passenger side from the intake to the metal line, over to the brake booster, is a good candidate.) But if it's unusual and black, check the AFM.

If you have come up with any other clues, let us know.

-John.

jeremy

iTrader: (1)

i'm glad i have people to expand on my terrible explanations of crap.

WackyRotary

The flapper expanation sounds better then mine. I do know that vacuum leaks that are large enough to kill the engine rarely go unnoticed for long. I always check my rear when the engine is running bad for some reason for what color is coming out the exhuast. Does it smell very gassy when it runs, then it would certainly be running too rich. But this is relative, all rotaries smell some. he he.

cammil

It was the Air-Flow flap stuck open. Thanks everybody for the help. It's running well now. Any suggestions on the best way to clean this / stop it from happening again?

FJ

Glad that's all it was.

You could disassemble the AFM and clean it thoroughly, but the small circuit board and flap-activated rheostat mounted on the board are delicate. Taking it apart and re-sealing it with silicon is not out of the question, however.

But chances are, it was just a little dirt buildup at the bottom of the tunnel, under the flap. I would use a rag and carb cleaner to wipe the area, and maybe spray a bit on the pivot side of the flap, but not hose it down. I wouldn't try to use any oil or WD-40 type lubricant on the pivot side; it would likely just attract more dirt. Chances are, that cleaning would be sufficient.

If that is not enough and it happens again, then you might have to take it apart. At least you know the symptom now, and it won't hurt anything if it happens again (except for fowling the plugs). I would try cleaning what you can reach first, though, just because a new AFM is rather expensive if things don't go well when you take it apart.

Anytime I remove the air filter, I wipe the inside of the housing with a rag and a cleaner, even if it looks clean. Seems to have helped, in the long run.

-John.