RPM surging +/- 200 rpms
 

I've found a lot of excellent advice on TBM in reference to this problem but I figure'd I'd throw it out here also in case someone else has experienced this maddening problem. At idle but mostly at the first throttle "click" or no-wake zone speed, the motor surges approx. 100 - 200 rpms and it's making me mental. My motor is brand new, with 27 hours on it but the intake is from my old motor so it's something to do with the intake/fuel injection setup. The advice I've received so far from LKSD, Boss232 & others is to clean my throttle body which I will do today and check the vacuum lines but, just in case it doesn't go away has anyone else experienced/fixed this ??? It really is annoying, any advice is appreciated. Rock

Give us some specs on the motor.

Is it a new Mercury EFI motor or a new motor from a custom builder?

On the Merc EFI the IAC Motor will cause that.

If you go to the Question & Answer section here on OffShoreOnly and post this question along with complete details of which engine you have you will get some VERY good feedback.

Good luck

It's a 2007 GM Marine Division 502 Mag MPI (415hp). According to my re-power mechanic, it's identical to a Merc. factory reconditioned 502 except it is all new. I'll post this to the Q&A section as you suggested but I wanted to give you the specs you asked for. Oh yeah, where is the IAC motor located ? Is it the round black part attached to the underside of the tb ?

Rock

There is a small brass screw-in air filter on the throttle body. This is where the idle air control gets its air from. Remove it and see if the problem goes away. I had this issue with mine and I ended up replacing the filter with a barbed fitting and then ran about 12" of hose to a K&N breather filer. Problem solved. The reason for the surge is that it cannot get enough air so the IAC opens then it sees more rpm then it tries to close right away and the result is an annoying surge.

You can also try... spray some storage seal into the hole feeding the iac, often salt will collect and or corrosion build up.The storage seal will help lubricate it so that it can work properly.
Jim

Ok, guys...thanks for the tips ! I'll let you know how I make out. Rock

Fixed yet???

No, not yet. I bought an IAC motor and a TPS sensor and am going to replace both just for good measure but haven't had a chance to do so yet. Boat is pulled and in my driveway...now, only if this rain would stop. Hopefully, by the end of the week.

Rock

502 EFI RPM Surging fixed !
 

Well, I removed the throttle body and cleaned it thoroughly with Merc. spray cleaner and installed the new TPS and IAC Motor. The freakin' surging is gone, thank God !! I have a feeling that I couldv'e replaced just the IAC motor and been fine but what the hell, the TPS was seven years old too. Question, I noticed a little bit of adjustment room when installing the new TPS. Is this just the design of the part or was I supposed to adjust it somehow when I installed it ? I'm just curious since the adjustment range is so small anyway. I'm just happy that the boat idles smoothly in the no wake zones now. :ernaehrung004:

Rock

anyone out there have this problem of running fine all tachs looking good then after a 1/2 hr or so i have the starboard engine tach fluctuating from 200 - 500 rpms but have no engine sound change or speed drop. is this a ground wire heating up? loose wire? where do i start? tanks in advance.kdawg