502 MPI idle speed
#1
Registered
Thread Starter
![Default](/forums/images/icons/icon1.gif)
My idle speed is at 750-800 according to my tach. Is it possible to lower the idle a bit. Possibly to 600? I got yelled at by the local sheriff boat today cuz he said i was going too fast through the channel. Told him nothing i could do, throttle was all the way back. He didn't turn around or anything, but i'd rather not be hassled at all. Plus, i wouldn't mind a slower entry speed to the docks.
#2
Registered
Join Date: Oct 2002
Location: Stockholm, Sweden
Posts: 379
Likes: 0
Received 0 Likes
on
0 Posts
![Default](/forums/images/icons/icon1.gif)
The engine should idle at 600 rpm. I don´t think it is adjustable. So, either the tach is faulty or it is in fact not idling. Could be that the throttleplates don´t close completely.
#3
Charter Member
![](https://www.offshoreonly.com/forums/images/icons/charter_member_star.gif)
![Default](/forums/images/icons/icon1.gif)
There is an adjustment on the throttle plates to open and close them at idle. You may try closing them slightly and see if the idle comes down. You may also need to clean the end of the Idle air motor-carbon on the end will hang it slightly open.
#4
Registered
Thread Starter
![Default](/forums/images/icons/icon1.gif)
Originally Posted by insptech
There is an adjustment on the throttle plates to open and close them at idle. You may try closing them slightly and see if the idle comes down. You may also need to clean the end of the Idle air motor-carbon on the end will hang it slightly open.
#5
Charter Member
![](https://www.offshoreonly.com/forums/images/icons/charter_member_star.gif)
![Default](/forums/images/icons/icon1.gif)
You will find an allen head adjustment screw on the throttle body near the air cleaner. It is the throttle plate stop. By loosening it slightly the plate will close down a little. Only make small adjustments so the IAC can catch up and regulate the idle speed.
#6
Registered
Join Date: Oct 2002
Location: Stockholm, Sweden
Posts: 379
Likes: 0
Received 0 Likes
on
0 Posts
![Default](/forums/images/icons/icon1.gif)
It may also be possible to adjust the throttle wire where it is bolted to the engine. If you take off the flamearrestor/air cleaner you should be able to see if the throttleplates close when throttle lever is in the idle end of the travel.
#7
Registered
![Default](/forums/images/icons/icon1.gif)
Agree that you should check the throttle cable to see of it's sticking a little and not allowing the throttle plates to hit the stop.
I do not agree that you should mess with the throttle plate stop screws unless you have ruled out all other causes and have a scan tool on the engine while you adjust it.
You have to first establish if the ECM is driving the high idle (high Desired Idle Speed) or if the engine is not able to achive the Desired Idle Speed due to other causes (misadjusted throttle cable, vacuum leak, bad IAC, etc.)
Dave
I do not agree that you should mess with the throttle plate stop screws unless you have ruled out all other causes and have a scan tool on the engine while you adjust it.
You have to first establish if the ECM is driving the high idle (high Desired Idle Speed) or if the engine is not able to achive the Desired Idle Speed due to other causes (misadjusted throttle cable, vacuum leak, bad IAC, etc.)
Dave
#8
Registered
Thread Starter
![Default](/forums/images/icons/icon1.gif)
Originally Posted by insptech
You will find an allen head adjustment screw on the throttle body near the air cleaner. It is the throttle plate stop. By loosening it slightly the plate will close down a little. Only make small adjustments so the IAC can catch up and regulate the idle speed.
#9
Charter Member
![](https://www.offshoreonly.com/forums/images/icons/charter_member_star.gif)
![Default](/forums/images/icons/icon1.gif)
It is accessible with the flame arrestor on but I will defer to Dave N on this one. Make sure you check all the other possibilities first before adjusting the idle screw. It fixed mine, but someone had messed with it. Check all the things Dave listed, then go looking for the screw.
#10
Gold Member
![](https://www.offshoreonly.com/forums/images/icons/gold_member_star.gif)
![Default](/forums/images/icons/icon1.gif)
Dave hit the nail on the head. Dont go adjusting things without the right tools, you can throw the sensors out of adjustment then you could run into idling problems as well as just off idle issues. Check out what was suggested before anything else.
John S.
John S.
![Big Grin](/forums/images/smilies/biggrin.gif)