Offshoreonly.com - 502 MAG Idle Problem

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Swap computer from good running engine see if problem transfers.

Quote:

Originally Posted by BUP (Post 4412293)

You need to post the serial number of your poor running engine and year modle

GM IAC for MEFI control systems really do not give as many problems as the Ford IAC - You have the GM. they are 100 times more reliable.

The TPS are more prone being the problem than the IAC for those apps

AFTER INSTALLING THE NEW IAC DID YOU SET IT ??? The GM IAC needs to be set after the install

I have a '96 7.3L that I just replaced an IAC on due to low idle and the manual said nothing about a IAC set procedure nor did the directions with the IAC. Can you point me in the area of said info?

Its in the manual 4 sure. i would have to grab it to tell you what page it is on.

Which manual are using ? Hopefully not a Seloc or Clymer

Who's IAC are you using ? you have to make sure you have the correct one. The pintle length , size, depth and shape have to be the exact as what the OEM had installed.

Power completely off anytime working on engine especially for fuel injection engines.

Anyways - new O ring needs to be used and sealing the IAC very well. Make sure all surfaces are clean including the air passage. Do not play with IAC pintle or try to jam the install with it. Install the IAC and the screws for it evenly torqued - then install Connections for that and anything else you had off. Turn power on after all of that is done.

resetting the IAC pintle position as follows

Turn the ignition key to the on / power position for 10 seconds - then turn it off for 10 seconds - water supply for engine cooling on - then restart the engine and check idle speed

Quote:

Originally Posted by Tidewater757 (Post 4412230)

I just bought this boat that has two 502 MAG MPI's one motor ran great across all RPM's and the other didn't like to idle and smelled very rich but ran fine at all other RPM's. I had the injectors rebuilt and install them and still had the same problem. I just installed a new Idle air motor and now it wants to idle at 2,000 RPM's. I swapped the MAP sensors, and the whole throttle body between the two engines and still had the same problem with high idle. You can plug the airport for the idle air control and it brings the idle down and will stay there after pulling your finger off, until you shut the motor off and restart the it goes to 2300 RPM's. Any ideas of what is going on??

I have found a boat with 1998 mag EFI's with bad intake Manifold gaskets from the factory. There was a tsb on them.I would think by now almost 20 years later they would have been changed by now but if it has low hrs ect... maybe not

Quote:

Originally Posted by BUP (Post 4423320)

resetting the IAC pintle position as follows

Turn the ignition key to the on / power position for 10 seconds - then turn it off for 10 seconds - water supply for engine cooling on - then restart the engine and check idle speed

Yup, a lot of GM vehicles and others do the same thing. Key to run, engine off closes the IAC, I usually wait closer to 30 seconds just in case.This way when you start it, the ECU knows the IAC was closed when started.

Quote:

Originally Posted by Tidewater757 (Post 4412230)

You have an air leak and have already found it in the IAC you replaced (the one where you plugged the airport and idle returns to normal).

Reset the IAC as BUP suggested (Key On, Eng. Off etc) and try again. IF the idle is now under control but its still rich we can look down other paths.

If the motor is still rich at idle check the yellowish tube coming off the VST and see if it is percolating liquid (fuel) into the manifold. If so that would cause your rich condition. This is an indication of an old diaphragm inside the VST chamber leaking fuel internally and out that vent.

Quote:

Originally Posted by BUP (Post 4423320)

Clymer manual is all I could find for '96 vintage.

I'm using a Walker Products 215-1026 IAC, new o-ring and TB gaskets used. Batteries were unhooked during removal and replacement. I did the procedure you listed above yesterday and it still stalls below having the throttle/tach. below 1k rpm. 1996 7.3 LX (FI) W/227 hrs. on it #OF884005 The bad idling engine doesn't hiss at "idle" nearly as much as the port engine, which idles solidly at 800 rpm. I guess the next step is to start testing the system electronically via the manual procedures.

Check and verify the ignition timing

Quote:

Originally Posted by Unlimited jd (Post 4426720)

Check and verify the ignition timing

Would love to but manual says to plug in a scan tool and switch to service mode for the procedure.