496 Vortex
 

I have a 2003 Gibson Houseboat with 496 8.1 Votex twins. 100 hours on each; port side delays and will not hold idle. Any suggestions?

Which are they? Vortex or Votex ? (hint: it's spelled Vortec)

Are the motors also 2003 models? Are they carbureted or fuel injected? Are they throttle body injected, or are they port injected? Are they stock or modified? What BRAND of marine motor are they (Volvo Penta, Mercruiser, etc)?

What do you mean by "port side delays"? and "will not hold idle"?

Does the motor idle properly in neutral? What is the idle speed?
Is the throttle linkage closing all the way when the control is in neutral?
If it does not idle well in neutral, at what rpm does it "smooth out" or at least "run without dying".

Does it only give problems when you put it in gear?

There are may things you need to tell us so that we may help.

MC

Sorry for the misspelling: yes, 2003 Vortec
Are they carbureted or fuel injected? Fuel injected

Are they throttle body injected, or are they port injected? Do not have a clue.

Are they stock or modified? Stock

What BRAND of marine motor are they (Volvo Penta, Mercruiser, etc)? Volvo

What do you mean by "port side delays"? The port engine only is giving us issues.
and "will not hold idle"? The engine dies and will not idle.

Does the motor idle properly in neutral? NO

What is the idle speed? Do not know what you mean. If it is in idle, it does not have a speed

Is the throttle linkage closing all the way when the control is in neutral?Do not know

If it does not idle well in neutral, at what rpm does it "smooth out" or at least "run without dying". 2000 rpm

Does it only give problems when you put it in gear? NO

You are obviously very knowledgeable and I apologize for being a novice. WE have had plugs replaced, sensors adjusted, fuel filters changed, and fuel injector cleaner in new fuel. Very disgusted; mostly because we have such limited access to adequate marine mechanics.

Bad idle air control (IAC) or improperly adjusted idle stop setting or throttle position sensor setting.

Thank you for the suggestions

If you cannot "creep slowly downward" from 2,000rpm and get it to run smoothly below 1,000rpm, then the idle stop is not going to be the problem.

The throttle position sensor (TPS) is mounted on the throttle body opposite the linkage. If you have a multitester, you can test it to see if it is outputting the proper voltages (google the wiring diagram and find the voltage spec online), and also you can see if it has any "dead spots" in the windings.

The IAC will affect idle, but you can isolate it from the system.
Unplug the IAC, start the motor and start bringing the rpm down from 2,000 and you should still be able to get it under 1000rpm. The IAC controls the idle speed, but with it disabled, you should be able to "manually" get it to idle under 1,000 with the throttle body doing the work.

If you still cannot get it under 1,000, then the IAC may not be the problem.

Keep us informed.
MC