I agree that a cone filter is a useless upgrade on this car but I think you have another problem.
Your 87 240 has LH2.2 engine management which is notorious for problems like this. My guess without touching the car is your AMM is either dirty or damanged. Try this experiment. Turn on the engine and unplug the AMM. If there is no change in the way the engine runs or it smooths out, your AMM is fried. The fact that it runs better between 40-50c intake temp is a sign that something is wrong with the AMM. Also having the intake stuck on the HOT side for a long time (the intake thermostat usually fails after 10 years) will damage the AMM. The thermostatic intake is designed to maintain a MINIMUM 20C intake temperature, not 40-50c. When the intake thermostat fails, it always fails in the HOT only side. Most people simply block off the hot side for improved FE and power.
Quote:
Originally Posted by FuzzyD
So if you have a "HOT WIRE" style MAF sensor in your car, Warm air intake is your friend! Also, clean the MAF every few months, dirty one is less accurate as well  |
From personal experience on half a dozen 80s and early 90s volvos, I think this is a recipe for disaster long term. The system is very aggressive about retarding timing and enriching the mixture as intake temperature goes up. You're not going to trick the system into running lean with hot air. Check your mixture and check your AMM. I think there is a good chance its damaged.
http://www.brickboard.com/FAQ/700-90...ettingBaseIdle
http://www.brickboard.com/FAQ/700-90...AMMCalibration
good luck
Justin