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rmasonshome
RO# 8978
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 Posted - Jul 26 2010 : 21:43:11
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2001 Mercruiser 4.3 EFI - Alpha Gen II - 520 hrs
Engine starts fine and idles correctly at about 800 RPM. After increasing throttle and returning to idle position - engine stays at about 1200 RPM (fast idle) - and won't drop back down to 800. Doesn't matter if it is in gear or not - reverse or forward. If I shut down motor and start again it will idle at 800 - until I increase throttle - then it stays at 1200. Shifting into gear at this RPM can't be good for the drive... Any ideas? Appreciate any suggestions!
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Sandy
RO# 1159
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Posted - Jul 26 2010 : 23:02:03
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Does it still do it if you disconnect the throttle cable at the engine and and manually advance and release the engine throttle lever?
Do you occasionally lube the cables, controls and linkages?
Check for carboned throttle body interfering with throttle plate?
Perhaps check for a dirty IAC muffler or if twins, swap IAC's?
Or better yet after the 1st check, , find someone with a MercScan tool & diagnostic manual and check for tripped codes &/or the IAC, TPS, IAT, ECT , MAP sensor and perhaps fuel pressure output to the ECM against spec or other engine readings if twins?
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| Sandy |
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Homeport: The Vineyard
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rmasonshome
RO# 8978
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Posted - Jul 28 2010 : 01:07:10
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Sandy,
Thanks so much for the suggestions. Here is an update:
- Disconnecting the throttle cable did not affect idle. I made sure the throttle was back to the idle screw - but didn't drop idle.
- I lubed up and inspected all the cables, controls and linkages (but they were in good shape)
- Throttle body looks real clean - no sign of carbon or dirt
- I didn't swap IAC
- I unplugged the Throttle Position Sensor (TPS)and the idle dropped down to 800 RPM - and returned to 800 after revving up the engine a few times. So, makes me think I have a bad TPS? If so, is it as easy to replace as it looks - (two phillips screws)??
- I haven't done the MercScan yet - perhaps I should before I go to the next step??
Suggestions?
Thanks for your help
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Sandy
RO# 1159
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Posted - Jul 28 2010 : 12:37:24
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The TPS should be easy to pull, but frankly I haven't had to do that .iif there is a problem with the TPS circuit there should be a code 21 set. Not sure if this could help on your Merc , but I just found this interesting advice for a Jeep TPS that mentions adjustment, so that may be a possibility or something to check on yours: http://autorepair.about.com/library/faqs/bl608e.htm That would be easier with the Merc scan tool that can access the TPS voltage data to the ECM. And of course a manual is always handy for specs and procedures. There's one for that Merc 4.3 EFI engine in the Mechanical How-To Forums .
Or perhaps swap TPS or IAC (only 1 at a time and put the other one back) with the other engine to see if it follows the part.
Just a boat owner-
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Homeport: The Vineyard
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D. Andrews
RO# 20354
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Posted - Jul 28 2010 : 20:01:20
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My bet is the tps, clasic sign and description......D.........
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Homeport: Mississippi
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rmasonshome
RO# 8978
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Posted - Jul 30 2010 : 19:03:34
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Here is latest update:
Took the boat out today for a hard run - 3200-4000 rpm for 5-6 miles across Lake Washington.....problem seems to have corrected itself. Perhaps some carbon buildup in the IAC??? All seems well now. Hope it stays that way. Thanks for your input.
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Billylll
RO# 24494
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Posted - Jul 30 2010 : 20:09:32
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High idle could be a vacuum leak or throttle body gasket if the problem comes back.
Bill
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WirelessOne,
40 Mainship
Sedan Bridge
Little Egg, N.J. |
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Homeport: Tuckerton, N.J.
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4.3 EFI won't idle down
