Symptom: 1)rough idle/ unable to accelerate above 2800 RPM. This only happens some of the time; sometimes it runs well. 2) Check engine light on- code=4 (crank angle sensor). 3) If the engine is started and the RPM is kept above 1500 RPM, the check engine light will not come on. Corrective actions taken: 1) Replaced sensor. 2) Verified (using factory service manual) the proper ohm reading to the ECM. Question: Could there be another cause other than the ECM? I need to be absolutely sure as a used ECM is $200, and a new one is $380+. Thank you in advance for your help.