Hi. I own a turbocharged 1990 740 wagon with an intercooler and have been having problems with lack of power in hot weather. If I stay in low gear for a while (driving downtown, for example, with controlled intersections at nearly every corner), the engine tends to bog down after about 15 minutes, and when I am able to go faster again it will not accelerate easily. This is especially true if I have to accelerate to climb any kind of incline or hill. This had not happened much before.

I have had A LOT of work done on this car in the last eight weeks, including a head gasket repair (to avoid the possibility of the gasket blowing entirely; the car had been leaking coolant but none had gotten into the engine yet; the water pump had to be resealed since it had already cracked). The ignition cap and ignition rotor were also replaced (a new ignition unit was put in last year). Two weeks after the head gasket repair, I had to replace the power brake booster (symptom: hissing sound whenever the brake pedal was depressed, along with spongy brakes). Just before I had the head gasket work done, I had the alternator belt replaced after it snapped. The alternator was replaced last year.

The shop that has done the repairs is a three-generation place that specializes in Volvos. The mechanics there thought the low-power problem might be related to the a/c compressor being slightly askew because of worn bushings holding it up, causing the a/c belt to run loose and wear unevenly. This could have accounted for the rubbery smell under the hood whenever I had problems accelerating.

The a/c belt and two bushings that hold up the compressor were replaced, but the problem with power still lingers, along with the rubbery smell, at least in warm weather. For example, in hot, humid weather yesterday, the car was fine driving to work and then at first while doing errands after work. The low power happened again as I was driving home and was stuck behind several slow-moving vehicles before having to climb a hill. I had put the a/c on briefly while bogged down in traffic. This would have been two or three hours after the hottest times of day, when the car had been parked in an exterior uncovered parking lot.

Any suggestions on what could be causing the low power? Today it is considerably cooler, and I have not noticed any power loss yet.

I've thought that the turbocharger could be affected by city driving in the heat. It has been desert-hot here the past few days (as high as 102 Heat Index, 90s with high humidity), and the turbocharger could be impaired. Other possibilities I've thought of: some kind of fuel gauge sensor, the oxygen sensor, the timing belt (which was replaced about 40K miles ago). spark plugs (which the mechanic says are OK), clogged fuel injector(s), or worst, botched repairs on the head gasket. The former owner of this car told me NOT to have bothered with the head gasket repair; he said it would have been better for me to keep checking the coolant leak, which had been becoming quite frequent.

I'm not a mechanic and have only a basic knowledge of the car's workings. I am at my wit's end dealing with this car's repeated breakdowns. It was driven as a California car for it's first 27 years of life, and since I brought it to a temperate climate last year it has not been doing well.