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View Full Version : 96 Prostar 190 high idle somtimes!


skiboyny
09-11-2011, 07:13 AM
Hi everyone,

I have a problem with my 96 Mastercraft Prostar 190 tbi that's been plaguing me on and off for years and now is getting more prevalent. It will at times go in to a high idle (about 1100 rpm) If I restart it may go back down to normal. It used to do this once or twice a year but just lately, It does it for a whole ski set until the boat really warms up. After it is good and warm it will run fine for the rest of the day. Anyone had a similar problem or might take a stab at directing me at troubleshooting this?

erkoehler
09-11-2011, 10:42 AM
Check the IAC.....

skiboyny
09-11-2011, 01:14 PM
Check the IAC.....

Thanks for the reply. Had the boat out for a few sets this AM condition is much worse now. Idling high more often than not. Is there a way to check the IAC or just replace? If I unplug it while running the idle goes even higher if I leave it unplugged for a minute and plug it back in the idle would come down sometimes. It has become unmanageable at this point.

erkoehler
09-11-2011, 01:34 PM
Just replace it.

dietdewboy
09-11-2011, 07:07 PM
whats an IAC?

André
09-11-2011, 07:09 PM
Idle Air Control.

skiboyny
09-11-2011, 07:41 PM
Just replace it.

I did replace it a few years ago. It was better by far but still would mess up a couple of times a year. I wasn't sure that it was the problem but the boat was very usable. I'll give it a shot again. Do you know if the IAC has a high failure rate?

Skipper
09-11-2011, 09:18 PM
Another cause of high idle is a vacuum leak....

skiboyny
09-12-2011, 05:27 AM
Another cause of high idle is a vacuum leak....

Thanks there are only a couple of hoses and they look real solid. Is there a way to check for a leak?

mikeg205
09-17-2011, 09:32 AM
put some new hoses in they are cheap...also make sure your firing order is correct. Indmar Engine manual troubleshoot targets, are IAC, Firing order, vaccuum, or engine module. I would also make sure everything looks very clean around the fuel and air intake.

skiboyny
09-17-2011, 04:29 PM
put some new hoses in they are cheap...also make sure your firing order is correct. Indmar Engine manual troubleshoot targets, are IAC, Firing order, vaccuum, or engine module. I would also make sure everything looks very clean around the fuel and air intake.

Thanks nothing should have changed the firing order I have had this boat since new. I ordered the IAC and throttle position sensor. The TPS came today I put it in and so far so good but I've been fooled before. The IAC has been changed years before it never really solved the problem but it would only show up on hot high humidity type days. (maybe twice a year) As of late it has been pretty steady. My hopes are a dead spot or noise in the TPS.

ahhudgins
09-18-2011, 08:05 PM
If your IAC is the type with the pintle on the end of the shaft, make sure you clean out the mating surface in the throttle body. You can keep replacing the IAC and still have intermittent idle due to dirt inside the TB because the pintle doesn't seat properly. Put a little carb or TB cleaner on the end of a rag and wipe it clean.

mikeg205
09-18-2011, 08:25 PM
good point ah... I always put seafoam and marine stabil in my tank cuz...I get on the water average one a week - or longer later in the season. You can run some seafoam right into the throttle body to clean things up. I lay up engines for 48 weeks in Ontario, CA and one of the biggest items that has kept the engines ready to start is clean intakes both air and fuel. Check the seafoam website they have a version of the product to spray right into the intake. I am lucky, my boat sits in my garage and I keep the dog house open to keep the engine nice and dry. Seems to help me.... wouldn't hurt to remove the IAC and spray a bit of gumout or seafoam to make sure the pintle seats like AH says...I laughed when I saw the pintle because I could not believe that technology is still used...same as small engine carbureators float control...

JimN
09-18-2011, 08:45 PM
Thanks nothing should have changed the firing order I have had this boat since new. I ordered the IAC and throttle position sensor. The TPS came today I put it in and so far so good but I've been fooled before. The IAC has been changed years before it never really solved the problem but it would only show up on hot high humidity type days. (maybe twice a year) As of late it has been pretty steady. My hopes are a dead spot or noise in the TPS.

Unless you actually do some diagnostics, you're going to piss a lot of money away by replacing parts in hopes that you'll find the cause. Dead spots on a TPS can be seen, but only with a digital storage oscilloscope. If you or someone has access to one, use it.

Check all of the grounds. Also, open the main harness and look for evidence of moisture. This could be a case of poor ventilation during storage allowing condensation to accumulate, causing contacts to become wet and then corroding.