Suzuki 250 four stroke Fuel Problem

[Walt4807]

One of my engines dies when reduced to idle speed. To start I have to put in neutral and increase the throttle then when I reduce the throttle to engage the engine dies. It will not seem to run below 800-900 rpm. Is there a diaphram that needs to be replaced?

[boats.net]

Might have a fualt with IAC valve, need to have it chevked for fault codes.

[Maninmanaus]

I have had a similar problem with my DF50. Unfortunately I wasn't that methodical in sorting it out, but draining the fuel tank of (old-ish - 4 weeks) fuel, replacing all the filters and cleaning the injectors resolved it. Good luck. Be interested to know what it was when you get it resolved.

[mitch]

clean your iac valve with some carb cleaner

[captfrankie]

Codes

I have the same problem. Very hard to get started first thing in the morning. How do you check the codes? I would gladly spend the $300 for the IAC valve if that will solve the problem.

[kmoose]

If it is not idling up at cold start and giving you problems at low rpm..... it's the iac. Try swapping out the iac from the other motor. I think you will find that solves the problem.

On thing to note: Do not adjust throttle stop screws trying to bump the idle up. Idle speed is not controlled by these and you will mess up the factory setting of the throttle bodies. All idle functions are controlled by the iac as it regulates low speed fuel mixture and speed by altering the intake manifold pressure.

The iac is a small stepping motor that runs a plunger in and out of an orfice on the intake. It is intrigral with a host of other sensors and functions for the low rpm control of our motors. Some times it gets gummed up and can be cleaned. In my case, the shaft locked up on the stepping motor and it didn't throw a code.

[redlowrey]

The IAC dosen't control fuel it only bypasses air, the base idle speed is set at the factory. The IAC controls the idle speed based on imformation sent to the ECU from sensors around the engine.

[kmoose]

The IAC dosen't control fuel it only bypasses air

Doesn't bypassing the air in graduation control air/fuel mixure by increasing or decreasing manifold vacuum?

[Harper]

Doesn't bypassing the air in graduation control air/fuel mixure by increasing or decreasing manifold vacuum?

No....it only bypasses air (same as throttle plate, air only). Mixture is controlled by the engine computer, which adjusts fuel amount and mixture according to many factors, by controlling the pulse width of signals to the injectors.

[kmoose]

No....it only bypasses air (same as throttle plate, air only). Mixture is controlled by the engine computer, which adjusts fuel amount and mixture according to many factors, by controlling the pulse width of signals to the injectors.

That makes much more sense put like that. Considering the 250 doesn't have throttle plate actuators it utilizes the iac stepping plunger to make minor air flow adjustments without interacting with the manual throttle body linkage. I wonder if the 300 uses the same methodology or just lets the electronic throttle body actuators handle that duty considering its a fly by wire?

Thanks for clearing me up on that.

[Harper]

I'm sure (at least 99.99% sure, since I'm not familiar with the DF300) that the idle air on the 300 is controlled by the IAC, and the throttling is done by a throttle plate, same as a cabled system. The conical plunger moving in and out of a machined seat is much more sensitive to minor idle speed adjustments, but the amount of air needed under power still requires the large throat and plate setup provided by the throttle body.

[1990corvette]

clean your iac valve with some carb cleaner

I am having this problem with my 2004 DF200 160hrs and also when in gear going foward, only can get to 2900rpm. The boat ran fine the 2 days before up to 4000rpm. I just bought it. All new gas lines, seperators, filters, IAC, fuel checked out good, bulb sucks down not flat but half full. No alarms. The only thing I did different than the previous owner was to fill the tank completely. He only kept it at 3/4full and filled with 2 red cans. Please help. Very frustrating for first boat, day 2 problems. I'm now thinking injector issue. Just can't believe it could happen that fast.