1998 Crusader MP-7.4l Xli's-Stall Issue

[mjk1040]

So recently my starboard engine on initial start up for the day is fine. If however I shut it down and go to start it again, it will start and stall, start and stall, unless I give the throttle bump up and back down, then it will start and run. I'm thinking IAC sensor or TPS sensor. Thinking that a previous owner had a couple cans of Carb Cleaner and tooth brushes in the dock box he regularly sprayed these sensors and tried to clean them? I attempted to remove them for a cleaning but it's impossible unless you remove the throttle body itself. Mind you that during the final winterization steps of the engines I will be checking, cleaning and changing the in line fuel filters, since I had some issues this year with the Oberg filters collecting some rusty matter, this along may be the issue. After looking at the break down diagram the only sensor that reads is the IAC that needs to be cleaned, the TPS just senses the throttle position if I'm looking at this right.

[bud37]

Seems odd you are not able to remove those without removing the entire assembly.... Tps is basically a variable resister so can wear in spots to create some dead areas over time( can be tested ), the Ecm requires that input along with the map to decide what is going on ........the Iac is a stepper motor that gets told what to do by the Ecm
You can clean the IAC carefully, the TPS is sealed.
What serial number is your engine?

[mjk1040]

Serial Numbers? Thought I had them on my phone! The TPS is in the way to remove the IAC, just a PITA and didn't have the proper angled torx bit to get in there. May come off if I had the right tool. Reading on the IAC it has to be clean for it to read write with no carbon build up. Thinking I'll get the right angled torx and remove it and clean it good.

[bud37]

The idle air control is not a sensor , it is just an electrically operated valve that the computer uses to control the air going thru a small port to control your engines idle , transition to throttle closed and transition to throttle open. If I remember you said you had a scan tool, hook it up and see what the IAC counts are at idle....should be around 40 to 60 tops if all is well. If it is a lot higher then the computer is probably trying to overcome something.They do need cleaning on the odd occasion, maybe a bit sticky, they also wear out like everything else, clean the throttle body plate itself as well.
Do you have the little filter/muffler in that port there?

[tomschauer]

Mike, hopefully this doesn't apply to you, but, dock mates have the same 7.4 crusader, 1998. They were having the same issue. Turned out to be an ECM. I wont tell you how much they paid for a new one.

BTW, due to continued bad weather weekends, I haven't had a chance to take pictures of the speaker install yet, but I haven't forgotten.

[mjk1040]

Thanks Tom & Bud, will have to wait till spring to hook up the scan reader on a live attempt, but could check for a code I guess, on the hard now. Think will try cleaning and/or replacing ICA first before going for a new ECM. Research of the ICA mentions my issue with a dirty ICA, it sticks and maybe the issue when the engine is warm. Erratic idle and stall on start up after warm.

[tomschauer]

My friends ECM didn't show any codes. He then swapped with the one on the good running engine and it ran fine. Apparently these ecms are not easy to find and are costly.

[bud37]

Mike there is something else you could do while waiting for spring.....have a good look at your plug wires, how they are run etc.......make sure they are not stuck up against any ground posts on the engine or over clamped pinched , clean etc.......have a good winter.......

[mjk1040]

Forgot I posted this 2 years ago. Issue came back, pulled and cleaned IAC,s. Thought I had it, ended up replacing IAC's and seems to have solved my issue. As always Thank You all for your input!