[Daveml]

I purchased a used 17 zforce 500 trail with 800 miles on it for my wife. only damage was from the machine going onto its side once. it was tipped onto drivers side.  it has a rough idle and sometimes will stall at idle. it has a flashing MIL light. I took it to the dealer before I figured out how to read the code. they said it had several o2 sensor codes. they tested the sensor and said it was bad. was gonna take over a week to get the sensor so I decided to order and do myself. had it in 2 days. they also tested the fuel and I had them check the valves and adjust them. fuel was good. replaced the sensor and no change. o2 sensor codes are still there as well.
since I got it back I tested the tps, and idle valve.
some observations I have noticed.
when I disconnect the wire to the idle valve it idles much better. also there is always power to that plug so the valve never shuts unless I unplug it. it seems that something is telling the ecn to leave that valve open causing the rough idle. if I disconnect the wire going to the map sensor as well it seems to run as it should. once warm will idle at 1450-1500rpms but it threw a high voltage code for tps so I tested that and it appears to work but I don't have the specs of the sensor which cannot be replaced without doing the whole throttle body.
battery is good. it runs great except idle. when letting off gas it backfires a little. old o2 sensor was black when I pulled it as well as spark plug. oh ya dealer replaced spark plug.
when I ran it without the map sensor and idle valve wires connected the spark plug looked better but not perfect.
I did a compression test and its at 150psi. any thoughts?
Thanks in advance.

[Daveml]

one other thing. when I got it the airfilter was clogged bad. I replaced the airfilter and sealed the box with dielectric grease on both sides of the gasket.

[NMKawierider]

With the MIL light still on, there is still some error somewhere. And with both the plug and the O2 sensor black its saying either it's very rich..which is tough to do with EFI unless there is a leaking injector, or there is something else being introduced...like oil or antifreeze. With the compression still at 150, the rings and valve seats seem pretty good. Is it loosing coolant? Anyway If you don't have the service manual already, probably get one and start going through all the sensors. I would also pull and clean with the proper cleaner the MAO/Air temp sensor and pull the throttle body and clean all of that and the idle air valve. I also think I would double check those valves and while there, inspect the cam chain and tensioners for an issue. 

[NMKawierider]

one other thing. when I got it the airfilter was clogged bad. I replaced the airfilter and sealed the box with dielectric grease on both sides of the gasket.

Let me guess...it had the original factory paper air filter with the foam prefilter in it...right? If so...bummer...better do a leak down test.

[Daveml]

photo of filter when I got it. plug photos are after I disconnected the idle valve and map wires and ran it for and hour at various throttle speeds

[NMKawierider]

Oh F'k yeah that's the OEM air filter all right. Don't use them....get a Unifilter.Plug's suety around the outside...usually means rich fuel charge.

[Daveml]

no loss of antifreeze. oil is dirty but not the worse I have seen. oil change is on the list. usually one of the first things I do but I have been chasing this rough idle.
I have the service manual but doesn't list specs for all the sensors

[Daveml]

as far as the airfilter the new one the dealer had was similar. im gonna get the uni. I plan to move airbox too but waiting till it runs correctly before I start chopping it.

[Daveml]

would be nice if I could hook it up to an automotive scan tool so I could pinpoint what is happening. the guy I bought it from said he didn't know how long the mil light had been on.

[doug80638]

Where in NH are you located?

I have a diagnostic cable and program you can use if you are close enough.

[Daveml]

I’m in Hooksett where are you?

[doug80638]

Pelham. About 45 minutes south.
I'll send you a PM.

[Daveml]

couldn't figure out how to reply with quote but this is my ecu
i have a 3 wire plug under dash power, ground and wire that goes to pin 26 on ecu(read wire i think)

[Daveml]

i posted photo of my ecu below

Pelham. About 45 minutes south.
I'll send you a PM.

[Dave K]

Hay Dave did you ever figure out the cause of the back fires ?  my 2018 Z Force 500ho is starting
act the same with 746 miles on it.

Thanks
 Dave K