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If you can press the gas pedal to the floor and the engine speed doesn't change (but changes slightly in pitch/sound), then your Throttle Position Switch is probably stuck or a wire going to it is broken or shorted. This is the device that tells the computer if your foot is off the gas pedal (and to keep the car at idle) and when you desire to accelerate (the computer should now look for sensor input from the Air Mass Meter and increase fuel flow to match the incoming increase of air). The Throttle Switch is mounted to the side of the Throttle body and faces the firewall on the driver's side. Follow the black accordian tube up to the Aluminum cylindrical throttle body and look for a black rectangular box with 3 wires going to it at the electrical connector (and the big flat side of the box faces the driver).
If the car can increase in RPMs, I'd work your way down the following checklist:
1. Vacuum leaks: Check all vacuum tubes and the big accordian tubes (small splits).
2. Blown Fuel Pressure Regulator (just above the distributor on the fuel rail).
3. Air Mass Meter is just about dead (possibly killed by a stuck airbox thermostat).
If you have any trace of fuel in the vacuum line to the Fuel Pressure Regulator, then the internal diaphram is ripped and it must be replaced. By the way, when was the last time you changed your fuel filter? If you're behind on your routine service items, I'd strongly encourage you to buy a Haynes book at your local Autozone or auto parts store and complete Chapter 1. The rest of the book is also very helpful and will help you diagnose and service just about anything else on the car.
Lastly, Volvos from 1980 to early 1988 had a wiring harness that was prone to deterioration (biodegradeable harness breaks down due to heat and time). If your car has not had it's wiring harness replaced with a newer version, this may be the cause of the problem. Check your sensors and switches first, but also inspect your engine bay wiring harness for signs of deterioration. The FAQ on this website has lots of good info.
If your existing harness looks to be in good condition, but you want to make sure that it is the 'newer' version, you will need to remove the passenger side right kick panel (plastic) after removing the plastic trim piece around the door frame there. You will now see the computer mounted to the inside fender of the car (says Bosch LH Jetronic on the case) and follow the wiring harness up from the computer. Somewhere between the computer and where the harness bundle goes through the firewall (about 2 feet after the computer) you may find a White and Blue tag with black numbers on it. If this tag is present then you have the 'newer' style of harness and should be deemed reliable.
If you need to replace your existing harness, check out Dave Barton's website to buy a used "newer" version that will not break down:
http://www.linkline.com/personal/dbarton/WireHarnesses.html
God bless,
Fitz Fitzgerald.
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'87 Blue 245, NA 228K
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