Throttle Control Issue

[Krutch]

Brand new '99 Epic21 owner here. The boat runs but has no response from the throttle. It will idle where it should, but when the throttle bar is pushed in, we'll be moving minimum speed until the throttle bar is pushed all the way. At "full throttle", the boat will gradually increase speed (slower than it should) until full speed is reached. Moving the throttle back down, the boat will slow to the correct speed for about 30 seconds before slowing back down to the same minimum speed. Having a boat with only two speeds (uber fast and dead slow) is no good for pulling skiiers.

The mechanics who worked on this claimed it was the computer. They reported they hooked up their own computer to it and that it wouldn't communicate back. In their opinion, buying and installing the ~$1100 computer will solve this problem, but they've given me reason not to trust them. In the vast knowledge of this forum, does this sound like the correct solution?

[wakejunky]

if you dont trust them WALK AWAY. replacing the computer is going to cost you $1100 and your boat still WONT be fixed. our boats can be a pain in the ass sometimes. biggest complaint when a problem comes up is no communication with the ECM. I have yet to experience a bad ECM on this engine auto or boat. It is possible but i HIGHLY doubt it.

the computer is not responding because you MUST have the factory tool with the toyota marine cartridge to access it. I work for a lexus dealership and our scan tool doesnt work either. same scan tool different card.

You say the boat is new to you, was it ever running the correct way? im suprized its reaching full speed. what octane fuel are you running?

if the boat does reach full speed id replace spark plugs and add some fuel injector cleaner to the gas tank. BG 44K or techron.

if you only get say 30 to 40% of throttle at wide open might be a Throttle Lever Sensor.

test like this- remove air intake boot/box. so you can see the throttle plate. turn key on. have someone move the throttle lever back and forth from idle to full throttle. watch and see if the throttle plate corresponds. if it does its good. if it only opens 30% and only at full throttle you have a bad Throttle Lever Sensor. 

Please Report back your findings before you replace the part. there is usually some mix up of the correct part to replace. Toyota/Lexus parts are expensive. Id hate to see someone waste money.

[blindside]

Sounds to me like the MAF (Mass Air Flow) Sensor or maybe a Throttle position sensor.

[wakehead]

I had the same problems, and local Lexus dealer changed a throttle lever sensor for about $500, and fixed it.
good luck

[lostatsea]

were do you crome from i.e. nc,,i am also a lexus tech and have a card for the boats

[cyclone]

Lostatsea, that's good to know that someone out there besides Capt. Rick has a scan tool that'll work on our boats. There are a number of checks in the engine manual with a multimeter that will help in diagnosing sensor problems. I'll try to scan the pages for the TPS today.

[6t8amxetc]

Hey Cyclone where did you get the engine manual? Is it for the boat specifically, or is it a car manual? Was there ever a factory service manual produced for these boats? Thanks...Ty

[Capt Rick]

I can email the manual

MSI0010571 WorkshopManual,VT300iMarineEngine,DD&VD     35  $33.33  $15.00   
Capt Rick

[6t8amxetc]

Thanks Capt Rick. I will probably order one the next time I place an order. Is this book specific for the boats? Is there info like the boat cooling system etc? Or is it just directly from the car service manuals? Thanks again...Ty

[Capt Rick]

The service Manual is specific to the marine engine. Nothing on the boat .

[Krutch]

Took her to a custom Lexus mechanic in Dallas and was charged a diagnosis fee of 3 hours at $85/hr. He changed the throttle body (used $400) and she runs like a dream now. Total cost: $800.

Thanks for the help!
- Capt. Krutch

[lilfoo2225]

im gonna go with wake junky on this one. my friends sat for over a year without stabil in it and 87 octane. did the EXACT same thing. wouldnt go unless full throttle was applied then it would gradually increase. so i decided to replace fuel filter and topped tank with 93 octane with a lil fuel injector cleaner. took about 15 minutes untill it ran old fuel out of it and started to run normal. runs like a top now! good luck!   Oh and merry x-mas everyone! hope everyone got those epic parts they wanted. lol! 

[lilfoo2225]

oh and ps. it would trip a code if it was anything else. start from the easiest then work your way up.  . also there is great people on here that are glad to help. keep us posted.