Surging at idle.

I have a 1993 Fourwinns 190 horizon with the ford 302 cobra efi/ OMC drive. Boat has been running GREAT. i start hearing a fluctuation in the idle jumping up and down. boat runs smooth at higher RPMS but at idle it surges up and down gradually surging higher and higher and eventually smoothing out for a moment and then surges again. i've tried the MAP sensor, IAC valve, TPS sensor, replacing the battery, cleaned the air filter, replaced the anti syphon valve not long ago, sprayed out the throttle body, fuel pump pressure is at 30 something psi. i haven't been able to find a vacum leak but i'm still looking. i'm so confused because it runs great at anything other than idle. any suggestions would be appreciated. thanks.

my next thought was possible the alternator? the electrical system isn't getting enough voltage? i looked at the gauge and its reading just above 12-13.

any input or suggestions would be appreciated

Re: Surging at idle.

Might want to take a look at the filter under the IAC . Are you troubleshooting or replacing? Make sure your keep alive wire has a good connection. Don't go by the gauge you need a VOM.

Re: Surging at idle.

I have replaced the IAC, TPS, MAP SENSOR, BATTERY. i tried each one with the brand new part and with the OEM part with no change. the keep alive wire is the constant hot wire coming off the battery correct?

do you think a bad alternator could cause the same problem? not enough voltage going to the EFI system?

haven't checked the fuel filter yet but i replaced the water seperator filter a while back and the boat runs fine at higher rps so i didn't think that would be the problem but i'll probably go ahead and replace those both.

Re: Surging at idle.

I've seen many engines show this when they want new spark plugs... When were yours last changed? Even if they are 'long-life' plugs... they're not. My 1000 hour iridium 'long-life' plugs lasted 200 hours, same as a 'standard' plug.

HTH,

Chris......

Re: Surging at idle.

It's an EFI. Get the thing scanned. Then don't just change parts, follow the diagnostic path. Any thing else is a guess.

The stuff you replaced was probably old and tired so leave it on there. But you still have the condition. It's time to diagnose.

Re: Surging at idle.

muc- i've replaced the IAC unit. are you talking about something different?

chris even if the boat starts with no hesitation and runs good at higher speeds do you still think it could be plugs? i would like to hope it could be that easy of a fix.

NHGUY- id get it scanned but its the old efi system. basically it just tells me if the system is running correct or not doesn't pull codes, if it would read codes i would have had it scanned a looooooooong time ago

Re: Surging at idle.

losiandy1 said:

...chris even if the boat starts with no hesitation and runs good at higher speeds do you still think it could be plugs? i would like to hope it could be that easy of a fix. ...

Click to expand...

That's exactly what mine does. Starts great, runs well at speed, but in the 1000-2000 rpm range it hunts badly, especially on the flushers.

Re: Surging at idle.

OK i'm pretty sure i found part of the problem. i checked the voltage of the battery prior to starting and it was at 12.69. i then started the boat and at idle it is at 12.34. and each time i shut the boat down the voltage of the battery drops. i'm hoping i've found the problem i'm just unsure if there is a voltage regulator seperate from the alternator or is it all one unit. any idea if there is a voltage regulator on that year model? i couldn't see one but i'm going to look some more in the morning.

Re: Surging at idle.

One more gasket down is the IAC filter/muffler, they don't plug up as bad as Merc's but they can. Belt dust is a common cause.
This EFI system is designed to be troubleshot with a breakout box and VOM. A blinking light is as far as this system goes.
Regulator should be internal.
Low voltage is one of many things that can also cause your problem.

Re: Surging at idle.

Muc- ok, i'll have to check that, i was unaware of that. yeah...the blinking light test seems a little vauge....ok, so the alternator/regulator are all one unit...bummer, was hoping to find the regulator to have it checked...Thanks for the help i'll let you know what i come up with.

Re: Surging at idle.

Did you ever figure out your surging problem