Bad TPS?

[Bulldog0156]

2005 Optimax 150, 378 hours, Serial # 1B069539

Last summer my engine would not stay idling. Took it in to the shop and they have since replaced the high pressure fuel pump and all of the o-rings and other stuff on the fuel rails (sorry, can't remember what all has been replaced right now). There were some issues with the shop getting things figured out correctly but finally this spring they gave it a clean bill of health including a lake test. I have taken it out twice since I got it back. The first time, I didn't get any faults on the smartcraft gauge but the idle was a bit high at start (630 rpms or so) before it settled down (still was fluctuating between about 520-580 rpms). Under load it was surging rpms between 700-2000 rpms. Example: at a throttle position of about 1400 rpms it would surge between 1100-1700. It has never done that before I took it in so I thought it was a bit odd and started questioning the "it runs great" comment from the shop. I didn't run it very much that time out because it was making me nervous. Second time out was mostly to see if the surging still persisted. It is, and now it's running even worse. Idle was a little high to start again before it settled down but it's still not consistently at 550 rpms which it always has been in the past. Seems like it's rich (smoking) and really hunting for the rpm range it is comfortable with. I turned it off and restarted it just to see if it changed and when I fired it the second time I received a TPS fault on the smartcraft gauge. I didn't run it past about 1500 rpms before I decided to call it quits.

I did have one TPS fault on the smartcraft gauge a year ago but I had chalked that up to an odd gremlin since it ran fine and didn't throw the code again. Now I'm starting to wonder if the TPS has been slowly going bad. Based on my internet research it seems like the issues very likely could be the TPS sensor going bad but I wanted to get a second opinion before I order parts. I am also wondering if this is a simple plug and play with the new parts or if there is any calibration that needs to occur. I am in the process of moving over the next month and I don't trust the local shop to fix it given my issues with them up to this point, but the place I'm moving to has multiple Mercury dealers that have techs that have seen an Optimax before and I trust to do good work.

I'd love to hear thoughts from you guys. I really want to get back on the water by the first of July once I'm moved.

[EuropeanAM]

Have you run the engine up on plane and at 3500-5500 RPM's?

Your idle description is essentially NORMAL operation. Initial start (especially cold) the engine idle will be elevated slightly and will eventually settle down in the 565-590 range.

There is an area in the throttle that, even brand new from the factory, would simply produce poor running performance, since the boat is neither idling NOT planing (it's simply running at higher RPM's and pushing water, likely with a lot of load on it). This range produces variables that simply can't be easily calibrated for, and since most engines spend very little time in this RPM range, the focus was on a balance that would keep the engine running within this range on a wide variety of hulls/load-scenarios, and not so much on a "perfect tuning". From 2500 RPM's and up, it's very well covered.

Just want to make sure you're not chasing something you perceive as a problem that may, in fact, be the "nature of the beast".

[leonreno]

I would definitely follow Don’s advice but I wonder if the reeds or maybe even the tuner (loose) were checked?

[Bulldog0156]

Prior to the issues last summer it ran great. Idle was right at 550 RPMs all the time and never "searched" for rpms all through the range. It ran so well prior to the issue last summer. The diagnosis was air in the fuel lines causing it to die after a couple seconds at idle and then after that fix they checked air/fuel pressure and it was low hence the fuel pump replacement. First time out after I got it back I did get it up over 5000 RPMs and it ran fine at that rpm range but second time out it was not running well and I was concerned with giving it any more throttle.

Tuner could actually be an issue now that I think about it. I occasionally hear a clunk when I trim the motor up far enough and it does feel like the motor is louder than the past. They did not check the reeds as far as I know. Another thing that I forgot to mention was the water psi is low at idle when it's running rough, like 0.7 psi. Impeller is pretty new (25 hours) and I had no previous water pressure issues until the current issues popped up.

[JOE54]

w/p is too low while replacing w/p tuner can be observed through exhaust housing opening ,take long screw driver and see if its loose or fell off , also check for more fuel in air side of system

[Bulldog0156]

Update: Joe was right, tuner fell off. Thanks for the help guys!