mercury 40 efi high idle

[criv]

I have a 2003 Mercury 40ELPTEFI that starts and runs great except that it idles at 1500 rpm. The throttle body and plate are clean and it is closing all the way against the the idle stop screw. It idles at the same 1500 with the throttle link arm connected or disconnected. The IAC, fuel injectors, CPS, TPS, MAP, MAT, and ECT sensors are all reading what my service manual calls for. I checked them with a multimeter by checking resistance and voltage through the whole range of rpm's and temperatures. According to my hand held IR sensor and the ECT voltage reading the engine is getting up to operating temperature. I sealed up the intake and smoke tested the engine but could find no leaks other than a little around the throttle plate shaft which I figured is probably to be expected. I do not have a tach on my boat so I am getting the rpm's from a TA 100 smart tach ignition analyzer. However I believe it is correct as it sounds like it is idling high and has a noticeable clunk when put into gear. I had access to another IAC and throttle body so I replaced them with no difference. I also backed the idle stop screw all the way out on one of the throttle bodies which got me to the 1500 rpm from about 1800 rpm's. I have called several shops in my area to have the diagnostics run on it but they all say they don't know when they can get to it. I am hoping it is something simple I am missing and not the ECM. I would appreciate any suggestions.

[cowtrimmer]

Ill move this to the merc forum for you.

[EuropeanAM]

Can you provide the Engine Serial Number? This will help us to provide the best info possible.

[criv]

0T755937

[EuropeanAM]

Two things to check:

1. Temporarily plug the IAT's open port. Does idle DROP?

2. If not- check for vacuum leaks.

NOTE: Don't make adjustments to the throttle plate stop. Doing so can result in mis-matches and problems with properly learning TPS position (as well as idle problems due to incorrect or improper IAT Duty Cycle).

If #1 and #2 don't locate the problem, I would get it to a very knoweldgeable tech that has the Computer Diagnostic System.

For future posts... recommend using the 4 stroke forum (just a couple more down the list). Obviously in this case the thread was moved here by another mod.

[criv]

Thank you for responding. Plugging the IAT open port does not decrease the idle. I blew smoke into the intake with a smoke machine and could find no leaks except a little around the throttle plate shaft.

[EuropeanAM]

You will need to get this on the CDS so they can reset the throttle plate for correct TPS range, and proper IAT Duty Cycle.

[criv]

I finally came up on the wait list to get my boat on the diagnostic software and it turns out it is running at about 900rpm's. My tach was wrong. All the linkages are set correctly and the inputs and outputs to and from the ecm are normal so I can live with 900. It did however show the voltage regulator jumping around between 10v to 12v. The fuse between the regulator and the solenoid was melted. This fuse is not in the parts list or the wiring diagram for my engine serial group though I do see it on other mercury serial group engines. When we removed the fuse holder from the circuit the voltage reg. is putting out a steady 13.3v I checked the wiring from the battery to the starter. All connections are clean and tight and the wire appears in good shape. Was this a retrofit from mercury? Do I need it on my engine?

[EuropeanAM]

Your engine's voltage regulator was replaced back in 2003 pursuant to Service Bulletin 2005-11.

The fused circuit is VERY important, and should be kept in place. Many of the other regulators Mercury offers also have this circuit now- the fuse blowing helps to prevent severe overloads (as well as overheating) of the regulator, wiring, etc.

MOST such problems can be traced to a problem with the Starting Battery, the Starting Battery's condition, Cable connections, cables, or battery switch. ALL connections must be CLEAN, secured with an appropriate NUT or LOCKNUT (never, ever use wing-nuts), and WRENCH tight.

Keep in mind- the regulator has essentially 3 jobs:

1. Rectify AC voltage to DC voltage

2. Pass DC voltage to the cranking battery until it reaches the maximum voltage setpoint in the regulator

3. DISSIPATE any excess voltage TO GROUND.

#2 requires that "Wrench Tight" connection to a good battery. Any poor connection between the regulator and the battery will result in excessive heat in that circuit (and can also cause the regulator to go full-output when it does not sense the battery on the circuit).

[criv]

EuropeanAM, Thank you for the information. I will get it set as you suggest.