Volvo: Lambda problem?, volvo 240 glt, lambda sensor

Question
One day when i was going to go home from work with my Volvo 240 GLT -91 Automatic. It did not want to start properly. The rpm going up/Down between 700-1100 rpm, and the lambda light was blinking. When i put more gas the lambda light went off.
I checked the engine and it was vibrating a lot. I checked the ignition cables. After starting and stopping the engine a couple of times the lambda light was lit all the time and the rmp changed to 1000, it was now running ok.
actions taken.
- Checked the fuses(in the engine room to).
- Checked air cables.(visually and with start-gas)
- Checked for sounds from the exhaust system.
- Changed lambda sensor. (located under the car)
- Tried to set diagnostic plug, after the lambda sensor change. (connector with
diode and plug for diagnose). Nothing happened.

It does have a speed holder that im not sure
working could that be related?

1 week prior to this event it passed the public car test (including exhausts gas measurement.)
After that i have replaced 1 rubber strap holding the exhaust system.  

Answer
I would check the idle sensor that tells the computer how to idle the car, that might not be functioning.  I would also check your throttle body; when they get dirty, they can starve the engine for fuel and cause erratic idle at times.  I would also go ahead and check your knock position sensor; a failure there could probably cause the same kind of issues.  Good luck!