Rpm jumping from 8-1100 at idle

Jumps back and forth and goes dead when put in gear. I gave it a little gas and got it gear and got back to the ramp but it was still surging. It didn't do it when I first put it in the water but only ran bout 20 for about 1/8 mile to my spot. When I cranked back up is when it done it. 97 pro max 200. Just bought a new cranking batt, the old one tested bad. Headed back to try it out. Put in and it was still doing it but I got going and out cleared up.seems to be fine for now.


Modified by Kevenater at 2:37 PM 4/22/2011

Voltage regulator bad.... Trace the gray wire at the rear of the two voltage regulators and the one thats hooked up to the butt splice is bad. You really need to replace both if one is bad...

Jay

thanks Jay!! I needed to update this sooner. the rpms are moving around, one min it'll idle at say 1800 and jump to 2100 etc, then next time it'll show 450 and jump to 6 or 700 etc. I can hear the rpm jump but it doesn't sound like it's idling higher than normal when the gauge is showing high rpms at idle. not that I can tell anyway. still same conclusion? once i get it in gear and gas down on it everything is fine. it's only at idle or barely on the pedal. now and then it'll idle fine for a min then start the eratic idle. thanks again Jay!!!! You're the man! about how much the regulators? i'll do both

Ask Don or Redline , I know they are pricey ( use only OEM Mercury electrical parts )

my .02
Jay

I am not trying to hijack your thread but I have a 96 225 promax that just started to jump at idle. It bounces from 800rpm to 1300rmp and sounds funny at idle. a fast half idle like its not on all cylinders and I have checked the wires with a timing light and have fire on all six plugs. It also started to shake and surge bad like a power pack is going bad. then it will run fine, then surge, then when I give it all the gas the surge will go away but if I cruise at 4000rpms it wil start bucking like a horse again. I have steady fuel pressure of about 34lbs. at idle. My question is can a regulator going bad cause the motor to surge up and down like your losing a powerpack or could the stator be causing the surging and rpm fluctuations at idle? http://www.bassboatcentral.com/smileys/praying.gif

Yes it can and BTW 34 lbs fuel pressure is too low IMO I like 40-38 ( no lower ) If your gauge is accurate...

Jay

You just described pretty much the exact same thing that mine's doing, lol so is it my voltage regulator or could it be something else? I was just bout to order a voltage regulator. Now not sure if it's that or the stator. btw isn't the voltage reg and a power pack the same thing?

Here is something else you can try. Mine and yours sound so similar maybe this is it. Tried running mine today and it still idles high and sounds funny again. I am still trouble shooting the problem. I noticed that the timing light will flash when I ckeck for fire but on the port side but even though the light flashes when I pull the top wire off the plug the engine does not change sound or rpm, even though the wire shows fire. I have to pull all 3 wires off the port side before the engine changes sound and rpm but will still run. If I pull the wires off the starboard side it changes sound with the first wire even more with the second wire and dies on the third wire. Is it possible for the power pack (switch box) that goes to the port side to still show fire with a timing light but not be hot enough and cause the engine to idle funny and surge at low rpms. Could this also be the reason why when I pull the wires off the plugs on the port side the engine never changes sound or rpm. http://www.bassboatcentral.com/smileys/praying.gif

I know nothing about this stuff!! lol I got my new regulator today. I didn't get the mercury cause I can't afford it right now. I got a sierra, maybe it'll last a while. I'm gonna post another thread with pics cause i'm not sure how to hook it up. it has a paper saying that it grounds through the block and not a wire like the factory one does. also i noticed on the passenger side reg. the gray wire is plugged with a rubber plug and doesn't hook to anything.