502mag won't start in idle, after warm-up can be backed down to 700rpm but stalls in idle position

[Controlled Burn420]

I have a 1996 502mag, the engine has been bulletproof for the 443 (fresh water) hours and 223 I have put on it. Only one issue, occasional idle fluctuation until now. This is the first weekend I have taken the boat out and it started fine, ran fine and idled fine for abour 5 minutes on the hose. I warmed the engine up and let it run at about 1800 rpms on the hose. After backing down the throttle to idle position, the engine wouldnt idle and stalled. Now it won't start unless the throttle is about 3 clicks off idle, I can back it down and get it to run in the 800 RPM range after warm-up but it seems to be a little rough. I also want to add that I messed with a few controls 2 seasons ago, the trottle linkage, and the little set screw under the air intake. Neither one of them seemed to do anything when I was attempting to adjust them. From what I remember I think I left them near their original position. After a little more investigation (6/23/13) I found that the adjustments I made would have not affected anything. Do you folks think this is an IAC , MAP, ETS, or something else. Should I just find someone to scan prior to replacing parts? Please help, I'm in over my head and wallet!

James
San Diego, Ca.

 

[phragle]

Scan it. save yourself time and money. Raylar might be an option, they are in Kearny mesa...

 

[old377guy]

Simple and dumb, but..... any vacuum caps missing? It happened to me.

 

[Controlled Burn420]

I have looked everything over and don't see anything missing or lose. I have also disconnected several components while running, and sprayed WD40 around most everything while running. No unexpected changes.

 

[MOBILEMERCMAN]

Scan it. save yourself time and money. I could be the IAC is sticking spray some wd in the tube in the inlet while running at idle. Could be a number of other things too. Just get it scanned and run next weekend. Or mess with it and hope to run one day soon.

 

[Controlled Burn420]

Scan it. save yourself time and money. I could be the IAC is sticking spray some wd in the tube in the inlet while running at idle. Could be a number of other things too. Just get it scanned and run next weekend. Or mess with it and hope to run one day soon.

Thanks Jim

I'm trying to find someone to come and scan, in the mean time I put WD40 in the air intake you described,it pools up inside, does not drain. I would assume that is supposed to control air flow at idle speeds when the 2 main flap valves are closed? Seems to be malfunctioning? Maybe just replace, it is 17 years old? I have had it running at several different rpms for over 1/2 hour and WD40 still pooled in the tube.

 

[Controlled Burn420]

Thanks Jim!

Just a few minutes after my last post I added some carb-choke cleaner. Shut the engine down and restarted a few times, it sucked the crap out of it and now idles better than it has for years. I sprayed some choke cleaner with it running and off, saw lots of deposits break loose, now looks spotless, at least what I can see. I'm going to leave some WD40 sitting in there until I run her next. Thanks for the $3.00 dollar fix, that was about the limit of my budget.

 

[old377guy]

Jim da man!

 

[Ratickle]

Jim da man!

Yep!