First thing I'd check would be the AMM. With ignition off, unplug the AMM then start engine. If idle is better it may be the AMM.
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1980 245 Canadian B21A with SU carb but electronic ignition and M46 trans in Brampton, Ont.

Since you are new to these cars, I will try to help you get a grasp of what might be happening when. A 1992 car should have a LH 2.4 or maybe a 3.1. I do not know about Motronic except it is Bosch and 1.8 means even less to me and a 240.

All the things that PAGEDA says are required maintenance. Once done on the car it will perform better and do so for quite awhile. Twenty-five city and up to thirty miles highway are normal for the engines with a foot conscious driver.

Stalling upon the transition from idle to power up can point to the throttle body. There is a plate adjustment and the position switch attached to it that tells the computer what you want to do. Dirt and scum affects the location of the edge that plate and its airflow. The incline you mentioned might be an in-tank fuel pump if the fuel tank was low on fuel. You should have more symptoms, at other times, if it was a definite problem.

Air amounts must match the computer map within the range the ECU can be capable to adjust or you will get an emissions check engine light. This happens if any kind of excess air leak behind the Air Mass Meter develops that the AMM cannot calculate.

You want to check for bad vacuum hoses and air tightness of the accordion tube behind the AMM. Look for cracks in the volutes with a light from shined from the inside.

Rough idle can be lean or excessive gas mixture. The lean condition covered above but richness can be the fuel pressure regulator he mentions of which fails by dumping fuel incorrectly. Either dropping too much gas back to the tank or letting fuel past its own diaphragm that ends up into the engine directly, unmetered and varies performances. The variance in fuel pressure affects injector spray that helps blows you mileage too.

The 0-2 sensor monitors the fuels final burning conditions. All of the electronics try to satisfy that fellow. If they cannot, you may, get codes that are a shotgun blast feature pinpointing the problem along with the idiot light. You will find out how good a shotgun works later. The sensor is in the exhaust stream of the down pipe and will have wires running along the firewall on the passenger side of the engine compartment. You can monitor it with the low range of a digital voltmeter.

Hope this helps you gain an overview of what a good manual will tell you. Find a Bentleys manual, it is our mainstay book and of course the help on this site.

Phil

Cleaning the throttle body, Idle air control valve, flame trap, and making sure the vacuum hoses and holes in the fittings are free to flow air is a very good place to start.

Remove fuse 4 to reset the codes and adaptive behavior ECU, drive it around fro 20 minutes and see what codes return.

20 mpg is not very good for a stick, check the vacuum hose on the fuel pressure regulator for gas odor.

Dan