Rich idle

[RichRab]

2002 merc I/o 5.0 mpi. Serial no. OM358103. Had trouble with rough idle last year. Have changed throttle sensor, iac, fuel filter, new iac muffler in throttle body and ignition items. No improvement. No beeping and had a merc dealer check it that was a waste of my time. He said if there is no beep there will be no code. I read that there is a map sensor. Can I check that myself with maybe a ohmmeter? Also was told by another mechanic that a computer will check things to see if they are not in range but possibly not throwing a code?

 

[alldodge]

Rough idle - I would start with checking plugs, wires, cap and rotor. If plugs do not provide any insight to running rich or lean, and there are no issues with higher rpm's, then my next thought would be fuel pressure or injector needs cleaning or replacement.

Need to do some diagnostics, check fuel pressure which should be 43 psi at 1800 rpm

 

[wrench 3]

Some of the hardest problems to find are when the computer is receiving signals that it recognizes but they aren't the correct readings. The MAP sensor readings can be checked with a voltmeter but you need a chart to compare the voltage reading reading to the manifold vacuum. Which I'm afraid I don't have.

 

[thumpar]

You might want to check with a different shop that has a scan tool. Not all codes beep and you can see what the computer is seeing when running.

 

[RichRab]

My son works on cars and they have a scan tool. Do you think it will work on my boat? Thanks

 

[thumpar]

My son works on cars and they have a scan tool. Do you think it will work on my boat? Thanks

No. Different tool.