Idle Air

New here. I have a 1999 Mercury EFI Bluewater #OG946773. Recently purchased it used. Found the idle speed was to high in and out of the water. Checked roller cam alignment. Idle stop screw was out of adjustment. Throttle was advanced in neutral. Alined the roller to the cam. Motor idled under speck rpm on the muffs. 600rpm. motor sticker says 625. I'm sure it show be about 800rpm on the hose. Found the top set of butterflies adjustment screw wasn't touching at all. Top butterflies completely closed at all times. can I idle the engine up with the top butterflies after I adjust the TPS or is it a TPI on this model?

Note: top screw has no factory paint and the engine was supposedly service at Basspro once a year. Maybe the previous owner has did some tinkering. Btw like you guys Iam read to hit the water.

Unless you are race tuning, the air shutters should all be fully closed, and should all begin to open at the same time. Back off the idle adjustment screw and set the shutters as per. Then adjust your idle stop so that the shutters are just beginning to open. Next, using your TPS test lead and voltmeter, set the TPS to spec. Now you need to put your outboard in the water, and set the idle (650 rpm, +- 50 rpm, according to the manual) with the idle adjustment screw.

Idle the outboard for 10 minutes or so, and check the spark plugs for rich/lean condition- you can make final adjustments with the TPS.

Thanks for the reply.Waiting to get TPS harness to get here. Everything is set for adjusting the TPS. Also found that the thermostats were removed. Ordered new SS set of stats today. Guess I'll see if the stats help with the rough idle. From what if has seen studying this outboard the top set of butterflies open like a secondary on a 4 barrel. When I get everything adjusted and installed I will take do the final adjustment in the water. If I have anymore problems I'll report back. Thanks again.

I put new thermostats in, adjusted my TPS. Idle is better but 0 to 9 ATDC is very vague. I set it to 6. Still didn't get to put it in the water this weekend. Had to set the top butterflies 3 or 4 turn out on the idle air screw just to get to 625 on inductive tachometer. The tac on the console say a little over 800 running out of the water. Tac on the console was 800 in the water before and it grinded into gear. I think the one on the console is more accurate. I think I'll set idle timing to 4. Then back out on the idle air screw. The problem I have now is the tale tale water is steaming a bit. To hot to keep my hand under it for more than a second. Should there be steam on the hose after 5 minutes on hose?

OH yeah! The engine alarms do not work and I have remove oil pump and reservoirs. Mixing 50:1. Water pump was changed 3 years ago and it sat a total of 19 months since then. 10 months and 9 months. It worked great without the stats.

You cannot set idle on a hose, it is set in water with backpressure. The 650+/-50rpm is in water in gear spec, on the hose about 950rpm is correct.

Go my water pressure gauge hooked up. Did compression test. 100, 110, 110, 110, 110, 115. Replaced water pump and poppet valve temp is much lower now. Found some piston top where looking a little shiny on the exhaust side and head gaskets are soft and brown at the bottom of the heads. Going to change head gaskets just incase. I'm thinking this engine may not be for from the machine shop. Hope they aren't to corroded. At the top where the stats go in there is some corrosion. Not much. This compression test was done cold and dry. Should I have done it at temp? And also wet? I have fogging oil. I did spray half a can of Quicksilver carbon cleaner in it after I ran it a few months ago.