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I have a '71 144S with B20B and BW35. I like my auto. Not much choice for me in New Zealand in changing and I have recently driven a 145 manual for a year so I know what it feels like, but still I like my auto.
Being an "E", you have the D-Jet FI which is an open loop controller and little advantage over a carburettor (if any). The "F" engine had mechanical K-Jet FI which is still the most accurate FI available. It only lacks from tuneability which is required for modern emissions control, etc. (Even though I'm an electronic engineer, I still would go for the mechanical K-Jet.)
The D-Jet has a number of problems. One is the obsolete pressure sensor on the intake manifold, at some point it will leak and thus measure incorrectly (it fails with a rich mixture). On the control module is a set screw for adjusting the mixture, if set wrong the idle speed will drop depending on load just like what the mixture setting does on a carburettor. Just like a carburettor, D-Jet can suffer big time from any air leaks in the manifold. The accelerator position sensor is exactly the same as a radio volume control, and how many of us have not had a radio with a noisy/intermittant volume control? The "computer" is a simple analogue circuit with zero diagnostics, it will not detect/ignore faulty sensors. The "computer" is wired with a lot of common/earth/negative wires bolted to the chassis with one bolt under the driver's seat where you easily get rust and bad connections, a single bad connection results in all signals making a bad connection.
D-Jet was a transition product where Bosh introduced something that could be called electronic to grab the market, yet had little benefit. Volvo used D-Jet for only a few years before switching to K-Jet, which they used for over 15 years until real computers made it into engine management systems. They had electronic systems in the mid/late 80's, but for turbos used K-Jet or else it would not survive. At the time the automotive computers were simply not accurate enough.
I would first check for air leaks (spray water on manifold joints while at idle, check for change in speed) and make sure the mixture is set correctly.
Just to make it clear, D-Jet and K-Jet are Bosch systems and not Volvo specific or designed. Volvo simply bolted it on just like a carburettor. Other car manufacturers had similar issues from the Bosch system.
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