I just bought a 1996 seadoo speedster 150, engines run fine but when i increase the throttles, the engines rpms quickly increase, but the speed stops like revving the gas on a manual transmission vehicle, and shifting it in nuetral. Rpms increase, speed doesn't until I decrease the throttles the speed slowly increases- on both engines! !

What is the fuel pump pressure? When you put the throttle down, there is not enough fuel to match the air inlet and it dies.

Hello Kit,well its the end of the season so if your really handy you need to change your prop and housing ring , the gap gets bigger over time and your jet prop gets smaller in diameter, letting high force water just pass by, just did the two of mine last year,same thing and now there like rockets!!!!!, cost =110.00-150.00 in parts , if dealer does it add 150.00 or so

When rpms are high, what happens if you stop,& put in park {while running} do rpms stay high or fluctuate ?

This car has computer controlled automatic idle speed control, the throttle cable is not likely the problem. Have the dealer run a special test to ID problems with this idle speed control system called an "Key on engine running fault code test"

You will find idle speed controllers in the area of the throttle plates. In order to work, air must bypass the throttle plates.

None of those possible problems have anything to do with idle speed. The first thing might be a very weak throttle return spring. The next would be a sticky throttle cable or foot feed pedal that isn't moving freely. Another possibility is a vacuum leak somewhere. Did changing the spark plug in #1 cylinder help the misfire? If not, you may have a partially plugged injector. Fixing the misfire will only increase idle speed some more. Look for an idle speed motor near the throttle body that is supposed to raise idle speed when the engine is cold and lower it back when the engine warms up. Check to see if it is holding the speed too high. If the throttle position sensor tells the computer where the idle speed motor is set, then it could have an effect on idle speed if the sensor is bad. The position sensor is just a fancy potentiometer. Hope some of this helps.

check the throttle position sensor. that should be whats wrong.

those sensors could cause the issue, clean the MAF 1st, also clean the idle system using the following procedure, the IAC can cause cruise surge. I use this to cure these problems all the time.

Here is the most common cause of surges and stalls and low idle, it is the idle speed control air-bypass valve (IAC) and throttle valve, they get full of gunk over the miles and cause idle issues (stalls, low idle) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake.

Check 02 sensors and the ductwork for all the air intake circuit. The EGR could also be the culprit...accordianman