idle is up at 2000 help
 

I just bought this boat so going in a little blind. It started fine ran great with plenty of power, but but then it started to idle at 2000 rpms and would not back down. here is what I have done.
first it is a 2001 merc 7.4 mag mpi 385 hp
took the iac valve off cleaned all of the throttle body
after that surges then give it gas and sticks at 2000 rpms

replaced iac valve -no improvement
took throttle cable off just to make sure it isn't sticking but samething happening

butter flys are closed and all the air is pulling from iac it seems
I can feel the air difference at the iac when it is surging so think the computer is making this issue happen but I don't have a scanner.
so hoping for new ideas

Sounds like a possible vacuum leak.

^^^ could be a leak, but check the timing as well. The computer also uses timing control the idle.

Mine was a broken intake gasket (after replacing the IAC)

also, get a rinda or other scanner on that engine to see that the IAC is actually moving.. could be the wiring to the IAC, ignition as suggested, vacuum leak etc

going to check vacuum tonight that was my next step I agree I need a scanner I have one for everything else I own

The new IAC wasn't recognized unless you put the engine in service mode. I'd get the scan tool (or just jump it) into service mode before anything else. It could just be the new IAC hasn't/isn't calibrated.

how can I jump it into sevice mode?

I believe it would be pins A and B on the connector. One wire is black & the other is black with a white stripe. Those are the wires to jump when checking timing. I'm thinking vac leak as well if it is surging it sounds like the IAC is trying to compensate. Randy

Alright checked for leaks can't find any vacuum is 12-15 surge was better after I reset iac but still idles at 1200 then when you give it throttle it holds at 2000. Throttle positioning sensor?

Have you checked the base timing as suggested?

Have you checked all the bolts and gaskets on the intake? They have to be REALLY cranked down (no rips whatsoever in the gaskets). I dont know the torque specs but if they arent tightened to spec you will have vacuum leaks which will cause the idle to skyrocket.

How many more parts are you gonna guess and throw at it before you check the basics?

You can also purchase complet scanning software for a pc, mefiburn.com. $199 for your computer

I agree I need to get a scanner 199 is a great price on it. I am trying to ck everything I can bolts all tight looked for any vac leak but don't see one. May have to leave it alone till I get the scanner

Or...jump pin a to b and check the base timing at 1800 :D

I think it was said that the throttle plate was closed - double check that to make sure its closing all the way at idle. Also I would have the motor scanned and especially take a look at the TPS = throttle position sensor.

If your worried about an intake leak, when its idling at 2000 rpm squirt some wd-40 or water along the intake/head junction and see if it sucks it in and if idle drops. Not fool proof, could have gasket leak on bottom of manifold.

Think I have ruled out vacum leak as I put handle of screwdriver over iac and it idled right down to 600 rpms and I could give it gas goes up fine and comes right down. So I am thinking if it was a leak I would not be able to make it idle down. So the iac is making it idle up. I checked the tp yesterday reads good. Am going to try pin a and b but not sure it will work as motor is 2001 and think I read that trick is for older motor but if it does I will ck timing

Pin A-B works on all MEFI controllers, which your engine has. My engines are newer and that is how I set the timing. After that an analog timing light will tell you where you are timing wise.

Got it will check

Correct me if I am wrong but if the throttle plate is closed, you plug off the IAC motor & it idles down, where is it getting air from? Randy

No I didn't completely cover the hole 80 to 90 percent. Yes plate is closed going to check timing now.

no i think you have found your problem,,if it idles good with 10-20% of the iac valve blocked,,,then what is the reason for having a large air intake at the iac,,,keep looking for a vac leak,,like randy was thinking

I am back thinking vacum also but here is what I did couldn't ck timing (never let your kids in your tool box .....light isn't working now)but got it in service mode no codes other than 12. Pulled then plenum retorqued bolts on intake they were a light looser than I would have liked book says 30lbs they were about 25lbs but still not right also checked iac plug two have power steady but two have nothing and book says all should be blinking power. Vacum is still a little low to be 10 to 15 that motor says 15 to 18 on pressure .
Thinking next think is to pull intake off and put new gasket on. What does everyone think worth the time.

alright manifold is good can not find any vacuum leak.but back to the iac was rereading manual and it says all for wires should be blinking from ecm it is mefi 3 ecm I only have 2 wires that are hot and they are both always on not blinking. could this be a ecm that is bad? just don't want to throw a ecm at it

all new stuff help idle is still high but we were trying to figure out if cover most of iac would idle fine ran great stopped it and now it wont start steady beeping.............when the key goes on have not looked any further yet doesn't sound like I am getting much of anything other than it cranks. it is a mefi3 manual says it should not be steady beeping

alright think the computer is out it has a steady beep when you turn key on and pulling code 51 on ecm. just happy I can stop looking for a vacuam leak lol I have replaced every gasket on intake..
with a code 51 I have read the ecm is just shot but where do I go to get ecm it is a mefi 3 and local deaqler wants 1500 for the computer alone as he said they don't make them any more. what is my best way to go here?