Fast Idle Issue

[Warlock28SXT]

Yesterday was out boat was running fine. Ran around a bit then stopped @ a local watering hole. No issues to this point. Got back to the boat smelled gas found the fuel filter came loose, my fault for not checking everthing after last run. Anyway fied and cleaned up and waited a while to be safe before starting. Now the issue after ideling back down the river I put the boat in neautral and the idle ran up to about 17-1800 RPM????? Shut it down cuz I sure as hell was not going to shift like this. Fired it back up and it was fine. Went back out on the lake and ran it, after slowing down same thing, fast idle. WTF? shut down fired again and fine. If I idle around it's ok but once I run it and slow back down it happens. Any ideas??????? Thanks Jason

[MERPerformance]

It's efi I take it?

[Warlock28SXT]

It's efi I take it?

Yes sorry its a 98 502 MPI .030 over(509) MEFI 1.

[MERPerformance]

Have you checked the idle air control

[Warlock28SXT]

Have you checked the idle air control

I have not looked at it at all. Looking for a place to start. Thanks merperformance

[MERPerformance]

Check the counts on the IAC, also what the ECM voltage is internally, you have a scan tool ?

[Warlock28SXT]

Check the counts on the IAC, also what the ECM voltage is internally, you have a scan tool ?

OK I probably take a look tomorrow. No I do have the MEFI Burn SW though.

[MERPerformance]

I had a ECM with a high voltage and the engine idle was doing the same as yours, make sure that you do not have an over voltage on the charging system, if so it will change the voltage in the ECM. My ECM had something wrong with it inside and would read a higher voltage than the batt. or charging system was putting out. Check the IAC first before you jump on the ECM, but do check it with a scan and code readings.

[Warlock28SXT]

I had a ECM with a high voltage and the engine idle was doing the same as yours, make sure that you do not have an over voltage on the charging system, if so it will change the voltage in the ECM. My ECM had something wrong with it inside and would read a higher voltage than the batt. or charging system was putting out. Check the IAC first before you jump on the ECM, but do check it with a scan and code readings.

Will do thanks. I have some files of runs prior to this to compare to. I have my fingers crossed for an IAC problem. I have a manual for values as well.

[Warlock28SXT]

It appears the IAC is bad. The counts on the IAC were 138 when @ idle. Shut off re start and the counts were at between 8-16. Manual states 0-40 counts (steps) is ok. I checked the plug with a test light, engine running test light grounded and touched all four connections. The light blinks on all four. Connections all clean. When it would idle fast the it was at the same RPM as with the sensor unpluged. Almost forgot the internal voltage of the ECM was 14.4 Vdc. Thanks again merperformance. I'll let you know how it is after the new IAC. Jason

[Warlock28SXT]

Should have the new IAC by Wed.

[Warlock28SXT]

Installed the new IAC. Key on for 10 sec key off for ten sec then started the motor. Idels right back @ 17-1800 RPM. What to do what to do.

After it sat for a bit I tried it again. Now it seems to be ok. I have to lake test it to be sure (bummer). I'll let you know what happens.
Jason

[Warlock28SXT]

Any other ideas? All things pointed at the IAC. Well now there pointing else where. Still does the fast idle after a run. Shut it down refire ok.

[Ratickle]

Any other ideas? All things pointed at the IAC. Well now there pointing else where. Still does the fast idle after a run. Shut it down refire ok.

Almost all the gearheads are at the race or runs this weekend (where I wish I were). You may have to wait till tomorrow eve to get guys back into this one.

[Geronimo36]

have you checked readings on the TPS??

[Warlock28SXT]

Almost all the gearheads are at the race or runs this weekend (where I wish I were). You may have to wait till tomorrow eve to get guys back into this one.

No worries. Thanks for the heads up though

[Warlock28SXT]

have you checked readings on the TPS??

I have looked at them. I know the count is zero when @ idle. I don't remember the reading @ WOT. I'll have to look.

[Magic Medicine]

sorry to hear your still having issues Jason

[Warlock28SXT]

sorry to hear your still having issues Jason

Thanks Andy. I'll get it. I'm off this week so I can look into it further

[Warlock28SXT]

have you checked readings on the TPS??

Do you or anyone know, is the step count for the TPS 0-100? @ WOT // TPS voltage 4.43 volts, TPS % 99.89. TPS step 64????