It is well documentated that in the JT8D engine (early 737's) the EPR will over-read if the EPR inlet tube ices up. Thus on take off with engine anti-ice off, but with ice blocking the inlet tube (that is part of the EPR system) the cockpit EPR gauge will show a higher figure than normal. This may cause the pilot to pull back the throttles until the EPR needles read correct take off EPR. The danger of that is that less engine thrust will be produced. Worst case is that you may have less than even climb power. Potentially deadly on a limiting length runway. That is why monitoring of the N1-which indicates the real thrust, is so important.
What is not often realised is that it is not only ice that can block the EPR inlet tubes. Some years ago a 737-200 came close to going off the end of a short runway on an atoll in the Central Pacific. OAT 30 degC. Investigation revealed that both EPR inlet tubes were blocked with a combination of coral dust and insects. These could not be seen during a walk-around inspection. Fortunately the captain firewalled both engines when it was obvious that it was going to be a close shave. A simultaneous double EPR mis-read was unheard of - especially as the only Boeing reference to false EPR readings was in connection with icing conditions.