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08 merc 5.7 surging

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I have had the boat for a couple of years 08 avy with 5.7 black scorp currently 510 hours. First issue i had was it would idle low or stall after returning to neutral. After replacing IAC this solved this issue however it still surges at a fast isle 1000 to 1500 rpm will not hold. for example after picking up a fallen rider. It wont stay at say 1100 rpm to fast idle to pick up rider. It will fall to idle then randomly surge back up and down. Runs great at all other rpm ranges.  Could this be the tps? 

I have changed plugs, wires, rotor cap,  going to change the fuel  water separator this weekend. 

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The throttle body might be dirty or getting worn.  Grab a can of carb spray and clean inside the throttle body, making sure to get the area around the butterfly really well.  That will probably fix it. 

If you still have idle problems after a good cleaning, you may need to adjust the idle stop on the throttle body to account for wear.  Basically, the air moving past the butterfly at near idle has to be in the right range so the IAC can control low speeds without hitting its travel limit.  Most never need adjustment after factory setup, but some do....


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19 hours ago, Woodski said:

@1HELLUVALIFE:  Are you shutting off PP or just not engaging it?  Try experiment with PP shut off, they can have a tendency to cause a surging when throttle is below set speed.

I want to say it does it either way, but i will test it hopefully this weekend.   

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I have seen some low speed RPM issues on black scorpion motors with perfect pass caused by improper throttle cable adjustment.  When the helm throttle is in neutral, see if you can move the throttle body lever on the motor where the cable is attached or if the two cables have slack or gap between them.  Adjust the PP brass hex on the throttle cable end, or the nuts on the "L" bracket so there is no slack between the brass hex and the PP cable housing.  Make sure the brass hex is threaded on at least seven turns, or more, and snug up the lock nut to it, so it won't break off the end of the throttle cable or come off.  Sometimes the little "L" adaptor on the throttle body lever may be flipped the wrong way or the throttle cable anchor bracket will need to be moved to get the adjustment right. 

On the Prefect Pass website, there are install instructions with pictures.  It says "With the  throttle  in neutral  position, adjust  brass  hex  connector  if  necessary to ensure  there  is  no gap  between  it  and the  end of  the  servo motor  cable  (any gap  may  cause  engine  to surge  up and down in neutral)."

I remember there was an extra page included with pictures and instructions just for the black scorpion motors whenever I ordered a PP kit for that setup, but it is still the same concept.  Call Mark at PP and I'm sure he can help you with it if you have any problems.

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