My 1991 745 Turbo has a problem that seems to be progressing, but goes away for a while at times.

At idle she will hunt, up and down, and slightly surge. Occassionally it will stall, because the idle drops low enough. But not all of the time, and sometimes it is more pronounced (severe) than others, sometimes not at all.

Sometimes she accelerates slightly weak, maybe with some surging and stumbling.

At cruise, she will sometimes seem to lack power, usually it is just barely noticable. Sometimes, she might suddenly "come to life" and regain her power. Sometimes she actually will hesitate at cruise, like I lifted off the throttle a little bit for a moment. The tach only starts to droop slowly and normally when she does this, no sudden drop like the ignition has cut out.

I know that one of the first solutions to the idle problem and the acceleration problem is to clean the throttle body and check the TPS, but I doubt that those are connected to the third, cruise, problem. I have just changed the fuel pump relay and the radio supression relay. No cure.

I am going to clean the throttle body tomorrow and check/set the closed throttle position and the TPS. Will also replace all hoses (some are original 1991 vintage, according to the printing on them!), and check for vacuum leaks, but somehow I don't think this is the cure for the cruise problem. The fuel pressure regulator does not have a ruptured diaphram. Idle does not really change that much when the hose is pulled off of the FPR.

Anyone have any ideas? While it seems to come and go, it is getting worse, and I can't afford to get stranded (the other two cars in my sig. are inoperative at the moment).
--
Scott Cook - 1991 745T, 1985 RX-7 GSL-SE, 1986 Toyota Tercel (Don't laugh, it is reliable, faithful AND gets 41 mpg!)