I have had similar problems in the past with my 1980 volvo hesitating during driving, and those times it was the fuel pump was "dying" and the other time the fuel injector was loose.
It has started "chugging" on take off and when climbing a steep hill. It also has started cutting out when going down the road or hitting a hard bump. However this time it seems to do it mostly when the outside temperature is either quite hot out or quite cold. Its really weird. When the temperature is moderate is runs fairly well..
We changed the spark plugs and wires, cleaned the distributor -rotor cap.
The fuel filter was changed a while back. The fuel injectors seem to be tight, as one time that was the problem- a loose injector.
I found out during the real cold weather when it was acting up that fuel line anti-freeze seems to sometimes help a bit. But wasn't a cure all.
It doesn't seem to be bad fuel , as the other vehicles run fine on fuel from the same gas station.
The only thing I can pin point that makes it worse ( is still cuts out from time to time) is pulling a hill or extremes of temperature.
I know it sounds real weird, but its true.
I wondered if maybe there might be a sensor problem- like fuel-oxygen sensor, because the other day when it was so hot outside, the car sounded almost like it was getting too much fuel like it was flooded, and it wasn't running well.
Would appreciate any thoughts.
Thanks

 

Well it has been a while since we have done much to try to fix the chugging, have been very busy. The car was off the road for a while, and once again the chugging problem was tackled.
The injectors were re-built, coil changed, spark plug wires were changed.
Even though we changed the spark plug wires were changed last fall, they must have been defective, because one burned through the rubber coating, and the fellow looking at the car got a decent shock off the wires.
These were Bosc wires, so I would have thought they would have lasted longer than 8-9 months…Changed the air filter
We thought it surely was “cured” but once again today the afternoon turned hot, and when I tried to drive it, it started chugging, especially when pulling a hill, or starting off from a stop sign.
Next thing we plan on doing is changing the timing belt, don’t know if that might be causing the problem or not.
I have no idea when the belt was changed, as I am unable to contact the fellow we got the car from…
Would an old or worn timing belt slip causing “chugging” when the temperature was extremely hot or cold?
Would an air temperature sensor cause the car to act up?
I was told that was a possibility..
Would really appreciate any thoughts..
Thanks

 

I thought I would give folks an update, maybe it will help others with similar problems..
We found a fellow who used to work on Volvos, and in about 15 minutes or less, he found a ,major problem which contributed to the car “chugging”.
The new spark plug wires were defective, had holes in them that had burned from the inside out! They were bosc wires too.. wish I would have saved the receipts.. they were only about 8 months old.. Grrrr..
After replacing those, the car still chugged.
He looked at it again and decided the car wasn’t cutting out, but “drowning” in fuel. He checked the hose going to the distributor cap, ( it was some sort of a vacuum line, I think) and there was fuel in that line, which isn’t supposed to happen. And there was a couple air sensor problems, and vacuum leak.
And to add insult to injury, some how the spark plug wires had a problem– firing order wasn’t right.. it was amazing the car even when down the road.
The firing order was fixed, the throttle body removed and cleaned ,and a new gasket put on to fix the vacuum leak.
The air box for the air filter with the corresponding air sensor was swapped for one that was on an old parts car, and one other sensor was tinkered with.
The car is running 95% better. Once in a while it still has a chug when there is a real fast acceleration, and it is thought that possibly a new sensor is possibly in order instead of one off an old car. Still needs a bit of work, hopefully that will happen in the future.
Anyways, even though it is an old car – it does have a few sensors on it, the one in the air filter box wasn’t opening or closing properly.
That combined with defective wires, the vacuum leak, firing order messed up, and the sensors not working. No wonder it chugged…