240 1980 240 wagon with strange idle problems

Hello, I have been trying to track down an idle problem on my 1980 240 manual wagon. So far I have changed the air intake manifold gasket, re-did the exhaust with the IPD performance exhaust for non turbos, and put in a new O2 sensor. Replaced the spark plugs, new air filter, flame trap kit and one of the temperature sensors (the one furthest from the fire wall), replaced the fuses and the fuel pump relay. The car will start fine then after a minute the idle jumps to 2k, it will drive for 5-10 minutes with no problem, then the temperature needle moves about 3/4 of the way up, it drives fine while cruising, but will die when I come to a stop. Any suggestions as to next steps to try and resolve this issue?

Does the car have AC installed? Make sure AC switch is completely shut off. There's a solenoid valve that receives power from the switch and the relay behind the center console. After a few seconds, the relay clicks on and engages the idle compensation circuit for the AC. On cars without constant idle (99% of the pre-1981 cars, some 1981-on cars), the idle bumps up to ~2000 rpm. If the AC doesn't work (or you never use it), you can remove the valve operated by the solenoid under the intake manifold and install an uncut aux. air valve hose. Then, remove the vacuum nipple from the idle adjustment screw assembly and put a plug in its place. That will cause the car to idle at 900-950 rpm at all times.

Your temperature gauge problem... Does the fuel gauge also go to 3/4 at the same time? If so, you have a bad voltage stabilizer, which plugs into the back of the cluster where the temp and fuel gauges are. If not, I'd check for a sticking thermostat. Maybe run an 82 deg C t-stat instead of what's in it. It'll run quite a bit cooler. Had an '81 242 with a B23E (Canadian spec 2.3 liter version of what your 245 has, with a hotter camshaft and no lambda-sond) that tended to run hot with an 87 deg C thermostat installed. Replaced that with an 82 and the gauge read just below the midpoint.