2002 5.0 TBI Mercruiser, no idle

[89 VIP Valiant]

Hello, working on my 2002 Crownline with a 5.0 TBI Mercruiser. New engine, working out all the issues. What it does is starts, idles perfect for about 6-10 seconds, then dies. If I bring up the RPM's to about 1500 or so, it will continue to run, then try to die and I have to feather the throttle to keep it going, then it will try to die again. So, I replaced the coolant temp sensor, still same issue. Unhooked the oil pressure senders, still same issue. Unplugged MAP sensor, same issue. Unplugged a sensor at the back of the throttle body(round connector, I think 3 prong) and if I let it idle, it will die. However, if I bring my RPM's up, it will continue to run strong, and will not try to die. So, I guess this is my problem? However, I don't know what this sensor is or what it does. A little more info on this boat, it sat for awhile and got lots of water in the fuel, i mean a lot. Caused significant corrosion to several components that i replaced, such as injectors, put kit in TBI, IAC valve, and fuel pickup valve/nipple on top of the fuel tank (I did replace it with a nipple I had without the valve/check ball inside of it). So, what does everyone think, is this sensor my probable issue? What is it? Thanks for any ideas.

 

[Kainon]

Re: 2002 5.0 TBI Mercruiser, no idle

Well, 2 things that i see can cause this problem ( at least ) is the IAC and TPS. the IAC - Idle Air Control Valve is for idleing and if the passages behind that are clogged or blocked, well.. that would do it. ( also if the seat for the IAC head is not clean ).. the TPS Throttle Position Sensor if not working properly as you can guess will also cause the issue.

Did you get the water out of the fuel tank ? Have you check the water/fuel separator ?

 

[89 VIP Valiant]

Re: 2002 5.0 TBI Mercruiser, no idle

Kainon, thanks for your help, and I have replaced the IAC valve, and yes I did pump all watered down fuel out. However, I didn't think that the TPS could cause a problem as I am having, could you explain a little more your thoughts on this? Also, do you have any knowledge on what that sensor on the back of my throttle body is? Thanks for any additional help!

 

[89 VIP Valiant]

Re: 2002 5.0 TBI Mercruiser, no idle

Kainon, also forgot to mention that yes, i have replaced the fuel/water separater, and then replaced it again last night when I was having this issue. The replaced filter did have some crud and moisture in it, but no change with the new filter installed.

 

[Tail_Gunner]

Re: 2002 5.0 TBI Mercruiser, no idle

If you run the motor and unplug the IAC valve and there is no change in idle after its warmed up..Thats your problem area...maybe.. Are your injectors firing a cone shaped stream thats uniform...Have you cleaned all of your male electrical connectors with contac cleaner and visually inspected them

 

[89 VIP Valiant]

Re: 2002 5.0 TBI Mercruiser, no idle

Yes, my injectors are spraying very nicely, so, does the engine running with that sensor unplugged not lead you to believe that has something to do with my issue? The IAC is new...so I had moved away from that. However, I did not try running it after warmed up with the IAC unplugged. Any ideas on that damn sensor on the back of the throttle body? What is it?

 

[Tail_Gunner]

Re: 2002 5.0 TBI Mercruiser, no idle

Yes, my injectors are spraying very nicely, so, does the engine running with that sensor unplugged not lead you to believe that has something to do with my issue? The IAC is new...so I had moved away from that. However, I did not try running it after warmed up with the IAC unplugged. Any ideas on that damn sensor on the back of the throttle body? What is it?

Clean your contacts well and inpsect them...If you run the motor with the iac plugged and unplugged and there is no change... ...The circut is either not working or not recieving any signal..either way its not working

 

[Kainon]

Re: 2002 5.0 TBI Mercruiser, no idle

Not sure of the sensor in the back, could be a MAT or Manifold Air Temp Sensor but think that's only 2 wires.

 

[89 VIP Valiant]

Re: 2002 5.0 TBI Mercruiser, no idle

Good thought about the circuit not working, and I had not tried running it unplugged, since it was replaced, but you may just have something there. I will check the sensor on the back of the throttle body, to see if it is two or three wires, but pretty sure it is three. Thanks for your help, will keep you updated.

 

[msmcada]

Re: 2002 5.0 TBI Mercruiser, no idle

Did you ever resolve you idle / throttle issue. I am having the same problem on a 5.7L TBI that sat for a long while with water in tank. I have done all the same step you have done but still will not idle and have to feather throttle to keep it running. The only way I can get it to idle is unplug the IAC and TPS....

Mike

 

[Don S]

Re: 2002 5.0 TBI Mercruiser, no idle

Welcome aboard Mike,
You really need to start a new thread of your own, with your engine, and a description of YOUR problem. Or your post will be unseen as other reply to the original problem.
Besides, the OP of this thread hasn't been back to the forums since June of last year.