The suspect, in his 60s, exposed himself to a victim before Junction Boulevard.
The 6, 7, A, C, D, E, F, J, M, N, Q and R trains are slated for service disruptions this weekend.
A Manhattan-bound 7 train stalled because mechanical problems mid-tunnel, the MTA said.
Commuters are using "7 Train Blues" to post about delays, suspensions and signal problems on the line.
Riders Alliance will send the stories to state lawmakers, urging them to fund the MTA's capital plan.
Erika Menendez, 33, pleaded guilty to first-degree manslaughter in the death of 46-year-old Sunando Sen.
Riders complained Wednesday of delays, service suspensions and packed trains on the line.
Councilman Jimmy Van Bramer is organizing a rally to protest poor service on the 7 line on Wednesday.
Monthly concerts will take place at the Bliss Plaza under the 46th Street station beginning in June.
The 1, 2, 3, 5, 6, 7, A, C, D, E, F and 42nd Street Shuttle will all be affected.
A smoke-filled station near Bryant Park snarled the 7 train, the MTA said.
7 train service will be suspended between Times Square and 74th St-Broadway from Saturday to Monday.
There were also delays on J and M lines and on southbound 4 and 6 trains on Tuesday morning.
Service along the 2, 3, 4, 5 and Q lines was affected by the MTA's "Cold Weather Plan" on Monday.
Trains were not running between Queensboro Plaza and Flushing Friday morning.
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