CDShack

Need a scanner. Could be ECU temp sensor NOT telling it the motor is warm, IAC as mentioned, you can look at short term trim and see if it's oscillating from a leak. With EFI engines, without a scanner, you're just throwing parts at it until it hits the right one. Good luck!

Trash

Faulty temp input won't cause high idle. Will impact AFR but not enough to cause the idle issue experienced.

Lafuerza

Took me a while but opened things up. Replaced IAC, Throttle Position Sensor, MAP Sensor, and cleaned out throttle body. Had injectors pulled and serviced. Fixed the idle issue. Got RPMs back up to 4800 at full throttle 1 person 1/2 tank of gas. Pulled 58mph on speedo so probably 55/56mph GPS. Still takes a bit longer than I think it should to pull get on plane but once on plane it pulls well. I have Bravo III with 22 pitch 3 blade props. I had same boat, 252 Super Sport with 502 mag with Bravo 1 and when I punched it you would be thrown back at this is at 6000' altitude.

I think I covered just about everything. Only thing left are spark plug wires (changed distributor cap, rotor, and plugs already. Compression was good 160 except for one rear cylinder at 140).

Scratching my head a bit. Internals???

Lafuerza

Forgot to mention took a scanner to it as well but mechanic didn't note an faults.

SB

iTrader: (1)

Thread was about high idle - what was the issue ?

F-2 Speedy

iTrader: (6)

if he threw all that at it at once ? who knows what the issue was

Lafuerza

Yes. I requested we do that. IAC and throttle body were gunked up badly. We put new IAC, Throttle Position Sensor, MAP Sensor, and had marine shop service Injectors. The boat sat for 3 years and we had fuel issues where I had to drain and clean the tank and all the filters so servicing injectors made sense and since he opened it all up it was all done at once. He only charged me 2 hours labor. Injectors were serviced for $250 so not bad in my book. I took it out today after replacing spark plug wires as well. Idle is 800-900rpm smooth and shifts like butter and I bounced off the rev limited at 4900-5000rpm. Temps stayed at or near 160. Sticker on my motor shows 4600-5000 operating rpm range. Hole shot was not glorious but good amount better and throttle response better too especially once on plane. Boat felt lighter on its feet overall. GPS had 54mph top speed which now makes sense with 22P props and old bottom paint. I just don't think the stock 454 Mag even with 385hp has close to the low end torque the 502 has with 415hp. If I can get some low cost 24P or maybe even 26P Bravo 3 props might throw those on there for fuel economy when cruising on the delta and will open up the top end as well. I'll keep 22P props for elevation (6200ft - Lake Tahoe) or even go down lower if I run across a reasonably priced set to help with altitude hole shot.

Thank you all for the help and guidance. I sure learned a ton restoring this thing. Got more to go but hopefully done with most of the gremlins I have been chasing.

Tractionless

Nice to hear of a solution for yours. Mine goes back to 2017 and still not solved!

Help Chasing Erratic Idle Please