I have been having issues with rough idle and surging. Also get a warning beep at startup and when under power. Took to a merc dealer and both tps sensors had a 100 plus codes. They replaced them and they are still getting the codes. Now after 4 or 5 hours of labor they said it could be the ecu. Yes I said COULD be. It is a $2000 part and they are not sure if it is the problem. They spent a lot of time on the phone with mercury but no one knows. I was wondering if anyone has had similar problems. Thanks in advance
1998 mercury optimax 135
They told me it had to be the ecu so I bought one off eBay found out yesterday that it didn't help. I took it to a mercury dealer/mechanic that was highly recommended. I am now $1400 in and they didn't fix a thing. They don't seem to care either. He says to me I'm glad optimax is such a reliable motor because they are really hard to trouble shoot and fix when something goes wrong. I have replaced the boat and motor already and the new boat doesn't have a mercury on it. This will be the last mercury I own. I can't screw anyone like the guy I bought it from so once it is fixed I will sell asap.
I would take it to a Mercury dealer that can properly diagnose what is going on and then stand behind it. 2000 is a huge chunk of change to spend on a hunch.