Idle varies, especially when cold

[ericml]

I have a really frustrating issue that I hope someone can help with. My 1996 Response with the Monsoon 320 engine has had a variable idle since I bought it earlier this year. When cold, it varies from about 1500rpm down to nothing and dies. It cycles from too low to too high and occasionally dies. Then when warm, whenever you start it the idle goes to about 1200-1500 for a while before settling down to 650 or so. Basically, a skier gets in the water, I start the boat, then the skier waits until the idle settles down, so I can put it in gear. A real PITA! I've cleaned the throttle body and replaced the gasket between it and the manifold and I've replaced the idle air controller and the throttle position sensor. I'm not sure what else to try other than a new temp sensor for the ecu or a new ecu. Also, forgot to mention that the cap, wires, plugs, fuel pump and fuel filter are all new.

If anyone has any ideas, I'm all ears.

Thanks much!

[UofM_MXZ]

Sounds to me like a fuel delivery issue. Have you checked the injectors? Sometimes they can have issues or it could be a tuning issue.

[axius]

You might be having a vacuum issue. Especially if you have replaced gaskets. Vacuum leaks will cause an accelerated idle.

The test for a vacuum leak is to have the motor running then spray starting fluid around the base of the throttle body. If the engine revs then it is sucking the starting fluid in through a vacuum leak.

If that is the case then you need to try a new gasket Bergen the throttle body and intake manifold. Careful tightening it down to get even pressure.

ski well my friends

[SeanQ]

I would second the vacuum leak

[dtm8119]

Did you do the calibration procedure outlined in the Clymer service manual when you replaced your IAC? Can you post a video of what happens when you start it up?

[JustinOSU]

Check the engine timing first.

[electricjohn]

A fuel pressure check is another thing to look into. You may have a bad regulator.

[Baddog]

I had similar wierd stuff 5-6 years ago and it ended up being the water temperature sensor, the one for the ECM not the guage. $30 part and I no longer got yelled at (unjustly, of course) in the no wake zone.

[Woodski]

Check the IAC - Idle Air Control unit. I have seen that be the issue.

[ericml]

I didn't know there was a calibration process for the IAC. Can anyone share that as I don't have a manual handy.

Thanks!

[dtm8119]

The Clymer manual states the following on page 411...

Step 13 (after installing the iac):

Start the engine, then put the engine into service mode. Take the engine out of service mode after operating at idle speed for a few minutes. Operating the engine in service mode calibrates the iac position to the ecu setting. Improper calibration can cause hard starting (particularly when cold), too fast or slow idle speed or stalling when returned to idle position.