Volvo Repair: 89 volvo studdering, fuel pressure regulator, example 121

Question
hey there, my 89 Volvo drives great most the time, but about a month ago after sitting for a couple hours in the middle of the day it began to idle real bad. As soon as it started it sounded like the engine wasn't getting enough gas, sputtering and hopping around.When we began to drive it only answered to me pressing the gas intermittently, driving very poorly. I got home and restarted the car, problem solved. Today, one month later, same problem, what do you think it is?

Answer
Probably failing air mass meter. But I've seen alot of EFI control units on this model and year.A failing fuel pressure regulator can also create problems.Or even a crank position sensor.Fault codes should be read off, recorded, and cleared. See which ones come back and when.Also check the fuel pressure, make sure its not leaking down.To check fault codes:There is a small black box located on the driver side under the hood in the rear. Place the probe in location number 2, turn the ignition on and press the button for 3 seconds. You will see a small red light flash a series of codes. You will get for example 121 one flash pause two flashes pause one flash. repeat this procedure until a fault code repeats itself. Then press and hold the button for 5 seconds and release the light should come on constant, then press and hold the button again for 5 seconds. That will erase any fault codes stored and return the computer to a base setting.Confirm the codes were reset by pressing the button again for 3 seconds, you should get 111. Take the car for a short drive and come back and reread the codes.Let me know what the codes are and we'll take it from there.