1994 5.0L EFI OMC wont run under 1000 rpm and wont start unless half throttle +

Hello,

I recently purchase a 1994 Four Winns wih a cracked 5.0L EFI OMC. I purchased a new long block and transfered everything from the old one over to the new one and installed it. The motor will start but I have to have the throttle past half throttle. The motor fires right up at that point. Since this is a new motor I don't like doing this and try to bring it down fast. I can get it down to 1000 rpm and let it set there and it runs smooth. When I try to bring the throttle back anymore or to the neutral position it dies. I drained the fuel tank and put new gas in it, new fuel filter, new plugs, distributor was a little corroded but not to bad. I checked the TPS voltage and it wasnt exactly to speck but was close and adjusted right along with throttle position. Removed the IAC solinoid and cleaned but could not find any test spec. Flame arrestor is clean. timming is set @ 5 deg. BTDC. Any ideas what my problem could be? Thanks!

Re: 1994 5.0L EFI OMC wont run under 1000 rpm and wont start unless half throttle +

What is the full model number of your engine, it will have the 50 plus letters following. First thing I would check is the firing order. Assuming you have a Ford, those engines will run really smooth with wires crossed, but will not idle right.

Re: 1994 5.0L EFI OMC wont run under 1000 rpm and wont start unless half throttle +

I recently had the same problem on my Mercury Grand Marquis. It was the idle air control valve. Replaced it and all was fine.

Re: 1994 5.0L EFI OMC wont run under 1000 rpm and wont start unless half throttle +

Got back to the boat today. No luck! Triple checked plug wires. Engine model number 50FAPRJUN. 351 firing order. 1-3-7-2-6-5-4-8. Removed IAC, cleaned, tested with 9volt battery. Solinoid seemed to work fine. Checked all vacum hoses and re-tourqed manifold to double check that I didnt miss any bolts. Everything looked good. Tried to start with throttle in neutral and it would try to start but I had to put the throttle up about half way and it would fire right up. Still wont run under 1000rpm. I put the spark checkers on and had good spark to all plugs. Put dielectric grease on all plug tips and unpluged all harness and sensor conections to put grease there to, hoping for something! I losened up the IAC thinking mabye the solinoid wasnt getting the messege to open and it would suck air thru the gap. This may have helped at start-up but very little if any. Still, when I slowly bump the throttle down around 1000 rpm it will want to idle a little rough, bump it back up a little and it sooths right out. If I let it get anywhere below 1000 it just dies like I turned the key off. Dont know much about the vapor seperator, could the float need adjusted. Should I try to set the TPS exactly to the specs in the book, as they are just barely off but adjust good when the throttle plate is moved. I am trouble shooting this with the drive off the boat still, should I put it back on for a little bit of load on the engine? I wouldn't think this would matter. Can I rule out a fuel issue? Open to any and all ideas! Thanks!

Re: 1994 5.0L EFI OMC wont run under 1000 rpm and wont start unless half throttle +

In your model number, you have a JV, not a JU which makes it a 1993 model.
Next, I would suggest you get the OEM service manual and check it "by the book", or you are going to hit and miss your way through the problem and may never find the problem.
Retorquing the manifold isn't going to help if it still has a vacuum leak, you need to get a gauge and actually check things, don't just assume things are ok because you looked at them or cleaned and looked at them. Testing per the manual may show that your cleaning didn't work or maybe made it worse.