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).
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Scott Cook - 1991 745T, 1985 RX-7 GSL-SE, 1986 Toyota Tercel (Don't laugh, it is reliable, faithful AND gets 41 mpg!)

Ok, did the throttle body cleaning today, replaced many hoses, checked the spark from the coil, checked the fuel pressure regulator by pulling the return hose and making sure that gas poured out, checked the TPS (with an DMM), and set the throttle position/TPS settings per the FAQ. Still have the same problem. Damnit

By the way, the fuel pump does have the black band that all the web sites show for the turbo models.

The only thing that I could find is that the in-tank pump appears, or sounds, to be dead. There is absolutely no sound coming from the tank, even when listening with an automotive stethescope shoved as far down the filler pipe as it will fit, or with the stethescope against the bottom of the fuel tank. Do you think this could be the problem? A dead in-tank pump has caused the main pump to wear super fast and now all the bad running at cruise, and idle problems are being caused by a dying main pump. Does that sound possible?
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Scott Cook - 1991 745T, 1985 RX-7 GSL-SE, 1986 Toyota Tercel (Don't laugh, it is reliable, faithful AND gets 41 mpg!)

mmmm... unfortunately I only have the usual "check your hoses" speech.

I would say the idle issue is the throttle body being dirty, but check the connections for the AMM/AFM.
With the hose off the FPR I would expect it to choke.......
Have you tried pulling codes? not all of them will cause a check engine light, especially not rich/lean at idle, even though the FAQ says it should.

Have you noticed it happens one way or another in cool weather or at night or something?
Also, how about the distributor cap and spark plug wires.

Good luck,
Will
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1990 740 Turbo, on its way to stock specs, maybe beyond

Will,

Fuel injection computer codes are 2-3-2, fuel trim too rich or lean at idle, and 3-1-1, missing signal from speedo. The 3-1-1 is normal for this car because the speedo is, well, doing the usual 740 speedo thing, and I haven't gotten around to fixing/having it fixed yet. But the 2-3-2 is not normal for this car.

There are no ignition computer codes, just 1-1-1.

Am doing hoses, etc. today as it needs them anyway. Will also check the fuel pressure reg. to see if it is holding full pressure in the fuel rail.

Last night I noted, at the FCP, Tasca Volvo, and IPD web sites that the turbo models, like mine, take a different fuel pump than the non-turbos. When I put the new pump in two years ago, I got it from a local non-dealer Volvo "specialist." Or so he calls himself anyway. I am going to see if the idiot gave me the right pump or not. They have different Bosch model numbers and on the three above web sites, the turbo pump has a black band around one end, the non-turbo model has a yellow one. I have absolutely no faith in this guy, over the past two years he has earned nothing but my contempt, so it wouldn't surprise me if he sold me the wrong fuel pump, which could explain alot.

Will report back later today.
--
Scott Cook - 1991 745T, 1985 RX-7 GSL-SE, 1986 Toyota Tercel (Don't laugh, it is reliable, faithful AND gets 41 mpg!)