I have had this problem for 2 years now. When I drive at a normal pace the car runs fine, but if I floor it, the car hesitates bad. The tach falls like 3-400 rpms and then comes back it jumps up and down till I get off the throttle. If I could try to explain the sound that it makes I t sound like its missing but just really bad. (boom boom boom.)

Here is what has been replaced in the last two years to try and solve this.

Main fuel pump

cap&rotor

plugs

wires

fuel filter

What else could it be? maybe the mass air sensor?

Please help

Ryan

Ryan:

If you have a turbo and the hoses are old, I would replace the inlet hose to the turbo. Mine had a very similar problem. When I replaced the hoses it went away. The hose was old and soft and would collapse when I accelerated hard.

since this problem is at high rpm I would look at your in tank pump. If the little rubber hose is slit like mine was or has a hole in it, it will suck air and cause that problem. also check your timeing. sounds like the in tank pump to me. i had that same problem.

Rick 87 740ti, 14 lbs. boost, turbo boost kit, cat back exaust, k&n filter

250 hp, stealth black, Napa Ca. Faaaaast!!!!!

The in tank pump eh? Well I think you can tell what my proplem is. It is really hard to describe over email but I think you got it. How difficult is it to replace it? Is it the hose you think went bad or the pump? I just go throught the trunk right?

First thing you'll have to do is to check your fuel pressure reg. Check it by disconnecting the vaccum line off it, the car should start to idle different, if it does, it is fine. Naturally also check all the ignition components, i.e. dist. cap, spark plugs, go put some bosch super plugs in instead of the current ones, also run an engine anaylser and check all the timing and dwell angle, etc. Not adjustable, BUT, if it is all over the place, then that indicates a problem with the ECU. Next is to check ALL earths, esp. the ones on the manifold. Your volvo (up to 88 models) were prone to (i heard it called this, and i reckon it is true) Bio-degradable wiring harnesses. Bsaically all the insulation disintigrates and the connections become bad....Next is to check the injectors, easiest way to do it is buy some injector cleaner and after you finish the tank of fuel, see if the car runs any better. After that check the air hoses, wriggle various connections, etc, and see if any wiggling makes a difference. Also, one other thing, disconnect the air mass meter, and the car should run REALLY bad (i.e barely run), if it doesn't run bad, then the amm, is the culprit.........after all this time of the stumbling and all, your O2 sensor, more than likely, will be stuffed. The amount of rich stuff going past it wouldn't have been good. Also, one last thing you MUST check, does the temperature gauge go to the middle always? If not, replace your thermostat. it will make the car run like new. If it hasn't been done recently, then do it anyway, as preventitive maintance. Hopefully that'll fix your problem buddy!

Have a good one

Check your fuel pressure regulator. If you can suck gas through the vacuum hose, your FPR diaphram is toast, and you should replace it.

Also, check your O2 sensor. Before you spend $150 or more on that, try this. I had a similar problem with my 1991 940 Turbo, and my mechanic suggested I replace my fairly new Bosch Platinum plugs with the copper electrode Bosch Supers one heat range hotter than spec. He speculated that the Platinums are not hot enough, and that led to incomplete combustion under high throttle. Have not had the problem since.

Once you replace the O2 sensor, you might want to try disconnecting the negative battery terminal overnight to set the ECU values to default.

I would try to replace the O2 sensor before the AMM. It's significantly cheaper and I experianced hesitation until I replaced mine.

Rene