2005 VP 5.7GXi-FF with rough idle and popping under load

[QBhoy]

Here is an update and a recap.
Sudden problem of popping under load.
Replaced plugs, wires, cap/rotor,and idol air control valve . Problem persisted, but maybe slightly less so.
Checked compression. Looked good. Mechanic said it was running rich from looking at all plugs and recommended replacing MAP sensor and coolant sensor. I replaced only the MAP sensor along with a different set of plugs (NGK V-Power 3951) their site matched them to my VP5.7GXI)
Engine idles smoother and no popping/backfiring under load at all or any time. Idle is slightly rough when cold. Idle fluctuates up and down from 650-1000, more so when colder. I suspect it still is running rich. Exhaust smells of gas more than normal. New plugs look black and oily/fuel covered looking.
I replaced coolant temp sensor and fluctuating idle improved did not get to take it out on the open water). Went back today to pull out for the season and cold idle is slightly rough and idle RPM still fluctuating, not noticeable when cold, but more after it warms up.
I plan to get a mechanic to look over the winter/early spring and check what I can when it is in storage (indoor/heated)

Thanks for all your help with this. If anyone has any ideas, please post.

Thanks!

Hi
I thought it would be iridium NGK 5599/5999 plugs for that. It is for all the mpi same engines.

 

[Rickenbacker]

Here is an update and a recap.
Sudden problem of popping under load.
Replaced plugs, wires, cap/rotor, and idle air control valve . Problem persisted, but maybe slightly less so.
Checked compression. Looked good. Mechanic said it was running rich from looking at all plugs and recommended replacing MAP sensor and coolant sensor. I replaced only the MAP sensor along with a different set of plugs (NGK V-Power 3951) their site matched them to my VP5.7GXI)
Engine idles smoother and no popping/backfiring under load at all or any time. Idle is slightly rough when cold. Idle fluctuates up and down from 650-1000, more so when colder. I suspect it still is running rich. Exhaust smells of gas more than normal. New plugs look black and oily/fuel covered looking.
I replaced coolant temp sensor and fluctuating idle improved did not get to take it out on the open water). Went back today to pull out for the season and cold idle is slightly rough and idle RPM still fluctuating, not noticeable when cold, but more after it warms up.
I plan to get a mechanic to look over the winter/early spring and check what I can when it is in storage (indoor/heated)

Thanks for all your help with this. If anyone has any ideas, please post.

Thanks!

Just picking up my post from last fall. (Volvo Penta 5.7 EFI -2004) Popping under load eliminated (I think) Irregular idle still may be an issue. (No loose cable). When pulling out last fall I noticed the idle rpm stick/jump to around 1100 rpm during docking. I discovered that when I took the fire arrestor off to clean during all the trouble shooting last summer I forgot to connect the large vacuum tube ( I think crank case fumes). The tube was resting on the throttle actuator. I really hope that was all it was. This spring I ran engine with a hose. It started fine, idle smooth, temp good. However, I put it in neutral to bring the RPM up to about 2000 briefly to see if anything sounded funny. From 2000 RPM I dropped it to idle as fast as I could and the idle would bounce around for a few seconds. From ~2000 it would drop to 0, almost stall and then up to 1200, then 100, then 900, then 500 and settle at normal idle (over a period of 4 seconds). I did this a few times. One time it stalled completely on the first drop. I suspect this is not normal even under no load. Any ideas? I still do not know if it is running rich or what underload will tell me.

 

[Rickenbacker]

I thought I should tell how it was resolved 2 years ago. I replaced the TPS (Throttle Position Sensor). Just used an automotive cross referenced part to save money. All issues went away.