Random engine trouble... HELP!!!
 

I'm having this really random, intermittent trouble with my 4g63 in my 91 GS. Every now and then when I'm driving, one of two things will happen: 1) the engine will start having what I can only describe as a 'coughing fit', which is cleared up as soon as I clutch in and rev the engine up to about 5000 rpm's or so. Or 2) the engine will suddenly start acting like it is fighting against something. If I clutch in the tach will drop to around 500 rpm's and if I don't rev the engine it will choke out. But, if I rev it up for a few seconds, it seems to clear the issue. I have spent a LOT of time thinking about this and I am completely stumped. The CEL only comes on during situation #2, but then turns off as soon as the issue is cleared, so I can't check for an engine code. The thing that really has me confused is that there are no specific parameters for either situation to occur. It did randomly all through this last winter and is still doing it every now and then in hotter, humid weather. I really would like to get this issue resolved, so if anybody has any ideas, I would appreciate any and all input. Thanks!!!

Mass air flow sensor maybe?