91 LS400 STALLING! HELP PLEASE

[Pacerdonfl]

RECENTLY BOUGHT, 140K MILES, HAD DEALER 100K SERVICE.

HAVEN'T DRIVEN IT MUCH, BUT FOR A FEW DAYS WOULD GO ALL DAY OR SOMETIMES LESS THEN BEGIN TO STALL. WOULD CYCLE FROM NICE, SMOOTH IDLE TO JUST BEFORE STALLING, THEN BOUNCE BACK UP TO NICE IDLE, THEN ALMOST STALL.....IT WOULD DO THIS A NUMBER OF TIMES AND FINALLY STALL/QUIT.

I COULD START IT RIGHT UP AND IT WOULD DO THE SAME THING, CYCLING FROM NICE RUNNING TO ALMOST QUITTING, THEN RUNNING NICELY AND FINALLY QUIT.

I COULD ALWAYS START IT BACK UP.

AS OF YESTERDAY IT WOULD START, AND ONLY RUN FOR A MINUTE OR LESS, THEN CYCLE DOWN-UP-DOWN-UP AND QUIT.

ALWAYS STARTS UP EASILY AGAIN, BUT STALLS W/IN 30 SEC TO A MINUTE.

I HAVE ANOTHER WORKING 91 LS400 - HAVE SWAPPED FUEL PUMP RESISTOR, FUEL PUMP RELAY AND INSTALLED A NEW FUEL FILTER. 

STILL THE SAME - STARTS NICE AND QUICKLY, RUNS SWEETLY FOR 30 SECONDS TO A MINUTE AND A HALF, THEN SLOWLY DROPS RPM. SOMETIMES WILL GET TO 100 RPM THEN BOUNCE BACK UP TO NORMAL,  THEN DO THAT CYCLING FOR 2-5 TIMES AND THEN FINALLY DIES.

ALWAYS WILL START RIGHT BACK UP....

ARRRRGGGGHHHHHHH!

 

 

 

 

 

 

 

[Exhaustgases]

Its good to have same car to swap parts with. Next try the air meter or some call it the mass air flow sensor, if you take it out of the aluminum body be careful reinstalling it, best to remove the whole airfilter and airmeter assembly to look in it when swapping, and if going that far just swap the whole unit.

Other things to look for are vacuum leaks, egr, and the idle air control valve also the engine temp sensor just replace it if its very old.