5.8 Cobra engine surges when Idling

[SpilledBEERMayday]

I have a 1993 Ford 5.8 EFI Cobra I/O in a Chris Craft 238 Concept Cruiser. Its the second year I have had the boat and took it out for the first time today and really noticed the engine surging while I have it idling. I dont remember it doing it last year. It starts fine, runs fine..........every now and then it will stall in neutral after I start it, run it for a minute, and ease back on on the throttle to the neutral position. The RPM's are not surging much from high to low.....but I can see the gage moving while the engine is surging.

At the end of last year, I noticed a hissing noise when starting the boat......I remember that it dissipated for the most part after it ran for a bit...........but this year, the hissing is not going away no matter how long I have the engine running.

Are these two issues related? How serious could this be? Can it wait to be serviced?........I just dished out some money on the gimbal housing.....so finances need to be rebuilt for a month or two.

Any ideas on what this could be would be appreciated.....I am far from a mechanic.

 

[Larson220]

https://lmr.com/item/LRS-9939A/1986-93-Mustang-50L-58L-Idle-Air-Control-Iac-Adjuster

 

[Larson220]

I had the same issue with my engine. Mine is a 1994. I researched this issue for and found that all of these fuel injected Ford engines of that era suffer from some degree of idle problems. All the issues revolve around the IAC valve. It is essentially an electronic valve that opens and closes via signal inputs from the engine sensors to open and close the amount of air that regulates the idle. Try the part that Is listed in the link. I replaced the IAC valve first, but the idle issues continued. Same exact symptoms that you are describing. I installed this part and voula, no more I'd l e surging or hard starting issues. On occasion when it is really hot out it will surge for a few seconds and it goes away. The part Will allow for a manual adjustment of the idle, like on a carburetor. The part will fit your engine, so if a repair facility or mechanic tells you that it does not. Find another mechanic that understands Ford engines. The downside of these Ford marine engines is that, not many marine mechanics understand them. Good luck, I hope you can get it adjusted .

 

[Larson220]

Ford dealer part # F2PZ-9F939-A

 

[Larson220]

I posted the Ford part number as well. Search online and you will have various options on where to purchase the parts. Good luck

 

[SpilledBEERMayday]

Very interesting information. Sounds like I will need to find somebody very familiar with OMC Ford to fix this.

Do you think I need to explore any other possibilities like an air leak.....the hissing makes me wonder. Possibly water in the gas? Just want to make sure I cover all possibilities....but it sounds like you went through the same thing.

Thank you for this information

 

[Larson220]

These fuel injected engines will make a hissing sound, mostly normal. It depends on where the hissing is coming from. The engine has a couple of vacuum lines. There is a pvc valve at the back of the engine. You may also want to make sure you change your fuel filter and always add marine stabil after you have added fresh gas.
if all of the above are in order, the part I listed in the previous post will surely help the surging idle. Good luck

 

[Funkymunky35]

I just bought an OMC that idles high and have ordered the part listed above. I've pulled the throttle positioning sensor off while the engine is running and it dies immediately. So I'm hoping this will solve the problem of high idle, but how is it installed? I've looked on Youtube and no luck.

 

[Larson220]

The part that I have listed goes between the iac- Aka idle air control and the throttle body. The part has two adjustment screws that allow you to set the base idle. Google all the terms that I have listed and it will be clear on how to install it, but most important you need to understand how to set the base idle. The part will help the surging idle. These engines will surge slightly even with this part installed, however with this part the surging is minimal, and you will have a batter idle that is steady.
Good luck. I would post pictures, but I am away from home at the time, no access to my boat.