surging (hunting) idle when cold....

Discussion in 'Gas Engines/Drives/Transmissions/Props' started by CliffA, Feb 1, 2018.

  1. atrick

    atrick Member

    41
    Mar 4, 2017
    Penna
    1995 searay 290 Sundancer
    1990 21 maxum
    Twin 4.3 mercrusers with alpha one drives
    305 chevy with a alpha one drive
    It happened on the girl friends suv, exactly what your boat did and she called me telling me the idle was going up and down and it finally evened out but give it gas would die but start right up with idle up and down then settle down, told her to let it warm up to temp and see what happened and still wouldn't take gas so she shut it off and sat there for 15 or 20 minutes till I could get there, started it up then and it worked fine. I at first thought water in gas or water froze in fuel line but when I hooked up scan tool it set 2 codes, 1 was IAC other was fuel actuactor, Hasn't done it again. A buddy and me went down to his boat a while after that just to check it and he started his engine up and did same thing, checked intake and they were iced up on outside, same deal let it warm up and everything was fine. Just a fluke with the right weather conditions. I would think the odds of your 2 engines with separate fuel tanks to develop a water in fuel condition at exactly the same time would be pretty high!
     
  2. hottoddie

    hottoddie Member

    953
    Jan 11, 2012
    Boston/Cape Cod
    1986 Sea Ray 390 Express
    Garmin 4212 Chartplotter
    Garmin 24 HD Radar
    Garmin GSD 22 Sounder
    Garm
    454 Crusaders
    May I suggest replacing the spin on water separators with the spin on Racor filters with the drainable bowl on the bottom. Make sure on an inboard boat you get the Racors with the cast aluminum bowl. The Racors with the clear bowls are only for outboard boats.
     
  3. BillK2632

    BillK2632 Well-Known Member SILVER Sponsor

    Jun 25, 2009
    Lake Norman, NC
    1999 185 Bowrider,
    Mercruiser 4.3, Alpha I
    So I did some looking into this last night (wife is out of town and I have time on my hands!). Carburetor and throttle body icing is a real thing - I don't think it can happend in a multi-port injected engine. Usually happens on a cold start before the engines have fully warmed up. The venturi effect in a carburetor or throttle body creates low air pressure and significantly cools the air going into the engine. When it is cold, but still enough humidity in the air, it is possible for the ice to form in the carburetor or throttle body. It is LESS likely to happen in very cold conditions as once temperatures drop into the teens, there is not enough humidity in the air to freeze. Pretty sure this is what was going on. Think about small airplanes, they have a heat circuit to heat the carburetor, this is why (my father had his pilots license and a small airplane - he was always yapping about carb heat) - in an airplane, there is not as much heat transfer from the engine to the carburetor due to the cold conditions and airflow around the engine. From my reading the conditions have to be right, but it can happen. In Cliff's case, once the engines fully warmed up it eliminated the freezing in the throttle bodies - a marine engine takes a good bit longer than a car to fully warm up due to the water cooled exhaust. Plus a car engine thermostat is typically 225deg vs 170 in a boat.

    So believe it or not -- I'm sticking to this story.
     
  4. CliffA

    CliffA Well-Known Member GOLD Sponsor

    Dec 29, 2009
    Lake Norman, NC
    2001 Sea Ray 340DA
    Name: 'Happy Place'
    4.5kW West. Generator
    Purchased Nov. 2014
    Fresh Water Use
    Twin Merc. 6.2L (MPI)
    Raw Water Cooled
    V-Drive Transmissions
    thanks for all the replies....I plan to stay on the boat this WE so I should have time to get deeper into this issue....

    cliff
     
  5. CliffA

    CliffA Well-Known Member GOLD Sponsor

    Dec 29, 2009
    Lake Norman, NC
    2001 Sea Ray 340DA
    Name: 'Happy Place'
    4.5kW West. Generator
    Purchased Nov. 2014
    Fresh Water Use
    Twin Merc. 6.2L (MPI)
    Raw Water Cooled
    V-Drive Transmissions
  6. Doc O Rock

    Doc O Rock Member GOLD Sponsor

    157
    Mar 23, 2016
    Great Lakes
    1999 380 Sundancer
    twin 7.4 Merc
    I never put fuel in the boat without a treatment. I just don't trust that there is no ethanol in the fuel, and even if there isn't, having an open system, the moisture in the air get in the tank.
    Put a good treatment in the tanks and double up on it, and run some through.
     
  7. CliffA

    CliffA Well-Known Member GOLD Sponsor

    Dec 29, 2009
    Lake Norman, NC
    2001 Sea Ray 340DA
    Name: 'Happy Place'
    4.5kW West. Generator
    Purchased Nov. 2014
    Fresh Water Use
    Twin Merc. 6.2L (MPI)
    Raw Water Cooled
    V-Drive Transmissions
    I ordered a case of STP water remover/fuel anti-freeze...I plan to use it this coming WE to see if it helps....

    cliff
     
  8. BillK2632

    BillK2632 Well-Known Member SILVER Sponsor

    Jun 25, 2009
    Lake Norman, NC
    1999 185 Bowrider,
    Mercruiser 4.3, Alpha I
    So did you run the boat this weekend? Same problem?
     
  9. CliffA

    CliffA Well-Known Member GOLD Sponsor

    Dec 29, 2009
    Lake Norman, NC
    2001 Sea Ray 340DA
    Name: 'Happy Place'
    4.5kW West. Generator
    Purchased Nov. 2014
    Fresh Water Use
    Twin Merc. 6.2L (MPI)
    Raw Water Cooled
    V-Drive Transmissions
    didn't get the chance to get into the issue.....we got to the boat around 3:00 after a 3 year olds birthday party on Saturday and friends joined us on the boat shortly after......then the drinking and eating started and before I knew it was 10:00PM so that day was gone....Sunday was cold and rainy and just miserable so I didn't feel like messing with things.....

    cliff
     
  10. CliffA

    CliffA Well-Known Member GOLD Sponsor

    Dec 29, 2009
    Lake Norman, NC
    2001 Sea Ray 340DA
    Name: 'Happy Place'
    4.5kW West. Generator
    Purchased Nov. 2014
    Fresh Water Use
    Twin Merc. 6.2L (MPI)
    Raw Water Cooled
    V-Drive Transmissions
    as a follow-up this past WE was warm for this time of year (high 60's) but was humid due to rain storms all WE.....on Sunday I started the engines and both started fine and idled fine....they both warmed up to normal operating temp of 170* without stalling.....

    both engines would accelerate as expected with increased throttle....but when I brought the throttles back to idle both engines would either surge a couple times and stall or would just stall immediately....

    both engines would start back up easily and idle fine but the surging and stalling when off throttle continued...

    the problem seems to get better once the engines have run longer say around 25 - 30 mins but does not completely go away.....usually after they run this long when I rev the engines and return the throttles to idle they will surge a couple times but settle down to normal idle of 650 rpms without stalling....

    I did not have a chance to check the fuel/water filters for signs of water in the fuel but these symptoms don't really indicate I have water in the fuel...the engines start and run fine with no hesitation or mis-fires....

    since the weather was warm I am leaning away from the theory the problem is icing of the throttle body as well...

    if I don't find any signs of water in the fuel next WE I guess it is time to call in a marine mechanic that I trust....good marine mechanics can be hard to find but fortunately I found one local to where I keep my boat slipped....

    cliff
     
  11. scoflaw

    scoflaw Active Member SILVER Sponsor

    Aug 10, 2011
    cape cod mass
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    Being a hands on guy, I would think you should own a scan tool, so you can see what the IAC and TPS are doing
     
  12. Strecker25

    Strecker25 Well-Known Member SILVER Sponsor

    Nov 20, 2014
    Rochester, NY
    1998 290 Sundancer
    Twin 5.7EFI/Alphas, Kohler 4kw
    I'd also like to have one of those. What is your recommendation without costing a small fortune? Is the Rinda one good enough for a diy guy?
     
  13. CliffA

    CliffA Well-Known Member GOLD Sponsor

    Dec 29, 2009
    Lake Norman, NC
    2001 Sea Ray 340DA
    Name: 'Happy Place'
    4.5kW West. Generator
    Purchased Nov. 2014
    Fresh Water Use
    Twin Merc. 6.2L (MPI)
    Raw Water Cooled
    V-Drive Transmissions
    yeah, i just don't want to spend the big bucks for a scan tool.....don't think I would use it enough to justify the cost....it would be nice to have though....

    cliff
     
  14. CliffA

    CliffA Well-Known Member GOLD Sponsor

    Dec 29, 2009
    Lake Norman, NC
    2001 Sea Ray 340DA
    Name: 'Happy Place'
    4.5kW West. Generator
    Purchased Nov. 2014
    Fresh Water Use
    Twin Merc. 6.2L (MPI)
    Raw Water Cooled
    V-Drive Transmissions
    my somewhat 'educated guess' is I have a problem with either the IAC valves or the TPS sensors since both of these can cause similar symptoms at idle....just seems odd that both engines have the same problem around the same time....

    cliff
     
  15. scoflaw

    scoflaw Active Member SILVER Sponsor

    Aug 10, 2011
    cape cod mass
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    I own a rinda, not familiar with others.
    First thing to do is hook it up to your perfect running engine and record all the values 1 screen at a time, so you'll have a baseline for when something does go wrong. Many adapters are available for it as well.
     
  16. BillK2632

    BillK2632 Well-Known Member SILVER Sponsor

    Jun 25, 2009
    Lake Norman, NC
    1999 185 Bowrider,
    Mercruiser 4.3, Alpha I
    Yeah, I agree it seems like one of those, just can't get past why on both engines at the same time.
     
  17. atrick

    atrick Member

    41
    Mar 4, 2017
    Penna
    1995 searay 290 Sundancer
    1990 21 maxum
    Twin 4.3 mercrusers with alpha one drives
    305 chevy with a alpha one drive
    You said it was humid, how about moisture in the distributer caps or on plug wires.
     
  18. CliffA

    CliffA Well-Known Member GOLD Sponsor

    Dec 29, 2009
    Lake Norman, NC
    2001 Sea Ray 340DA
    Name: 'Happy Place'
    4.5kW West. Generator
    Purchased Nov. 2014
    Fresh Water Use
    Twin Merc. 6.2L (MPI)
    Raw Water Cooled
    V-Drive Transmissions
    didn't check for that but I will next WE.....

    thanks.....

    cliff
     
  19. howie58

    howie58 New Member

    3
    May 25, 2015
    wisconsin
    1999 340 Sundancer
    Twin 7.4 merc I/O Bravo III
    I have had this happen with my 99 340 dancer with 7.4s in the summer once in awhile through the years if I haven't run it in awhile, Doesn't do it very often so I really don't worry to much about it. Boat has low 700 hrs on it and still works. One thing to look at, and I'm sure these boats have it, is a mass air flow sensor, I think that would also do that.
     
  20. CliffA

    CliffA Well-Known Member GOLD Sponsor

    Dec 29, 2009
    Lake Norman, NC
    2001 Sea Ray 340DA
    Name: 'Happy Place'
    4.5kW West. Generator
    Purchased Nov. 2014
    Fresh Water Use
    Twin Merc. 6.2L (MPI)
    Raw Water Cooled
    V-Drive Transmissions
    thanks but my engines do not have a MAFS.....they use a MAP sensor in conjunction with a TPS instead.....

    cliff
     

Share This Page

Show Sidebar