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By TPS you mean throttle position sensor, right?
On non-turbo models, it has two switches, on turbos it has two but only one is used by the ECU.
One switch is "Idle" the other is "Wide open throttle". The middle pin is ground for both switches.
Sometimes, people mix up connectors for the cold start injector (not present on all models/configurations/years) and the TPS.
The dash lights make sense, so long as it's only with a brief low engine speed.
It sounds to me like your idle system is not working - either because the throttle plate isn't staying shut, the idle switch isn't working, or the idle air control valve isn't working.
What I would check is that the idle side of the TPS works and that the IAC (Idle air control valve) works. There are a few ways to check this and to clean and lubricate it (I don't recommend using brake cleaner). I would also check to make sure that the TPS clicks when throttle plate is opened/closed.
A lot of people "fix" a broken idle system by shortening the rod between the throttle spool and the throttle plate or by lengthening the throttle stop screw. If someone's fiddled with either, you'll need to adjust the throttle plate position and then maybe the TPS (but probably not).
This thread http://www.brickboard.com/RWD/volvo/1323069/220/240/260/280/throttle_position_switch_never_closes_2.html might be useful to you for the theory, though it's talking about the 90 240.
You may be able to check the TPS for continuity by probing another set of wires elsewhere (like at the ECU).
Good Luck!
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740T and 244DL - Frank the Tank @287K mi. and The Polished Turd @237K mi.
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