VP 5.7GSI Idle and Cold Start Issues

GeorgeDes

Petty Officer 2nd Class
Joined
Sep 30, 2013
Messages
107
Been having cold start and idling issues with my VP 5.7 GSI (PWTR). The engine will start immediately if I hold the throttle open in neutral and will idle fine as long as I keep the throttle handle pushed forward and the RPMs around 700-900. As soon as the throttle is pulled back the engine rpms sink and it begins to stumble and eventually stalls. Under load running after warm up appears to be fine, but holding a steady idle with the throttle in neutral is not consistent making docking a chore. I have replaced the rotor, cap, plugs, plug wires, IAC valve, ECT, MAP sensor, both hi and low fuel pumps and the fuel filter/water separator . All with OEM parts. I also cleaned the TBI. Still have same idle and starting issues. I have only owned the boat for 2 seasons and had some idle issues that appeared to be cured for a while with the installation of a new IAC valve last season, but these same issues have arisen again this season. Going through some old maintenance records provided by the previous owner, I see where he was experiencing some high idle issues a few years back. The shop included an entry that pointed out "HI Idle--Computer scan--adjust min air so IAC works better--IAC will need to be replaced soon". My question is how is the min air adjusted? Is this a computer re-flash procedure or an adjustment to the base timing? From my experience dealing with auto engines, I know that adjusting the timing even slightly will change the engine rpms. I have the codemate reader and understand how the timing needs to be adjusted while in service mode but before I tinker with that I'd like to get some ideas. Thanks
 

tpenfield

Moderator
Staff member
Joined
Jul 18, 2011
Messages
17,621
The computer program is not adjusted. Usually it is an issue with the sensor(s), in this case the IAC sounds like the culprit.
 

GeorgeDes

Petty Officer 2nd Class
Joined
Sep 30, 2013
Messages
107
The IAC is an OEM and is brand new. All the sensors are also brand new. Has me stumped. Especially, the cmt in the old mtn report that says idle was high and they adjusted the minumum air to make the IAC work better.
 

GeorgeDes

Petty Officer 2nd Class
Joined
Sep 30, 2013
Messages
107
Well another interesting wrinkle. Made it over to the boat to try out the Codemate EFI tester and see if the ECM is resgistering any codes. Found the DLC connector and tapped into it according to the instructions. The Codemate light did not illuminate at all. Fiddled around with it a bit and still could not get it to illuminate. Now I'm bewildered because I was still able to start the engine and it ran fine as long as the throttle was kept in neutral and pushed forward to allow a fast idle so I'm guessing the ECM is working. Not sure what the deal is with the Codemate. Could I have a defective Codemate tester? If so, how can I test the tester?
 

GeorgeDes

Petty Officer 2nd Class
Joined
Sep 30, 2013
Messages
107
Got a test light out and tested the pins on the Data Link Connector (DLC). The F pin that supplies power from the ECM to DLC had an open circuit. After a few hours of painstakingly unwrapping the engine wiring harness, I was able to find and repair the broken wire. Once fixed and with Scan tool connected through the DLC, the scan tool lit up. Only code showing was Code 12 indicating on board diagnostics are working. All tests on the sensors were negative as far as I can tell. I'm thinking there may be a sticking throttle linkage that was the root cause of the original idle and starting issues. A previous owner had the min air adjusted for a too fast idle. It may well be the min air was adjusted too low. Will investigate this further but that seems to be where this is leading. I have a new throttle cable on order and will adjust the min air setting back up a bit if the throttle sticking is due to the cable being corroded.
 

bigbrownbuku

Master Chief Petty Officer
Joined
Sep 17, 2004
Messages
885
Have you tried removing the iac muffler in the throttle body, it can sometimes be blocked. You might want to pull the throttle body and check the iac bypass port Isn't blocked with an old muffler. Pull your iac and get someone to cycle the key on while you hold the iac nozzle(or it will bugger off at a high rate of speed) check it is actually responding to ecm commands.
 

GeorgeDes

Petty Officer 2nd Class
Joined
Sep 30, 2013
Messages
107
To close this out. I know it has been a long time! It turns out I had one cracked head and a burnt valve on each of the heads. The TBI also needed a rebuild. Two reconditioned heads and the rebuilt TBI cured all the issues I was having. Now purrs like a kitten!
 
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