What observation is common with an engine idling rough and stalling in gear?

When an engine is idling rough and stalling while in gear, a common observation is a contaminated throttle body. This condition can lead to poor air-fuel mixture management, which significantly affects engine performance. A contaminated throttle body can impede airflow and cause erratic engine behavior. Deposits built up on the throttle plate can restrict movement or disrupt the air-fuel mixture, resulting in stalling or rough idling as the engine struggles to maintain optimal combustion and operate smoothly.

Other factors, such as ignition module damage, leaking fuel injectors, or defective spark plugs, can also contribute to rough idling but are not as frequently observed in conjunction with the specific symptom of stalling in gear under typical conditions. The throttle body's condition directly relates to the air intake critical for fuel combustion, making it a prime suspect in situations involving rough idle and stalling.