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Very Rough idle after spark change and mystery wire.
Hello All,
Please see the Mystery wire picture at the bottom.
Noob's to the 300zx's as we bought a nice low mileage 85 non turbo, base, non digital dash 300zx 2+2 for my son about two months ago with 83k miles on it. Auto transmission. Been awesome until now after about 1k miles for us.
We have some maintenance records for the car with the timing belt changed at a local Nissan dealership back in 2015 and it now has 13k miles on that timing belt. Also have records the distributor was replaced 5 years ago and the car has a history of rear brake issues and warm start problems. It hasn't been modified in any way that we can tell and the previous owner was not aware of any changes either.
I downloaded the factory service manual already and it helped me fix the rear brake noise we were having and I have read quite a few of the posts here and cannot find an answer to this new issue and got confused.
The car ran great and had a very minimal uneven idle sometimes like a possible misfire. Not surging or changing RPM's, just an intermittent very light idle shake when hot. As we didn't know the plug history we decided to change them.
It had NGK wires and plugs and from searching it appears they were oem replacement parts along the way. The plugs in it were NGK-BCPR6ES-11 like the owner's manual indicated and all looked good and firing cleanly upon inspection.
The number one plug wire was so fused/stuck on the plug it tore upon removal. Went and had to get an aftermarket plug wire set as no auto parts store here had the NGK wire set in stock and couldn't get one for 4-5 days.
I needed the car before then so went and installed new NGK-BCPR6ES-11's and the aftermarket plug wire set. It ran terrible after this. I noticed a crack in the distributor near the number 2 terminal so went and got an aftermarket cap and rotor from CARQUEST.
No change with the new the cap and rotor and after sitting overnight it idles even rougher than yesterday. RPM's hold steady at 6-700 but the car shakes bad with a definite misfire(s) now. This morning I put back in the old NGK wires except the torn # 1, left the aftermarket #1 wire and left the new plugs in it. No change. Unfortunately I already threw out the old plugs to try them back in the car as I have never had a bad plug issue before.
I thought I had it tracked down to # 6 cylinder this morning and a bad plug as it ran no worse at idle with the #6 plug wire disconnected but testing the new sparkplug out of the car with a digital meter seemed to show it was ok. There was a noticeable change in the idle when I disconnected the other plug wires individually but not with # 6 disconnected.
I know brand new plugs and wires can have issues sometimes and I have another set of NGK plugs and NGK wires now on order after not wanting to wait 4-5 days, and now the car is out of commission for 7-10. Big sigh....
I am out of ideas. Any ideas would be greatly appreciated. I know we violated the first rule of avoiding a pain in the butt being "If it isn't broken don't fix it" and now I really have to fix more.
Fixing your kid's cars can age you fast.
I noticed this unconnected orange mystery wire from the wiring loom near the Idle up solenoid where I was working between #2 and #4 plug wires. I noticed it when I started and don't think I knocked it loose. It has a female connector and looks like it slides on over a post type connection. It only has about 8 inches of play and comes out of the wiring loom for the idle up solenoid so it should go somewhere over on this left side of the intake plenum as shown. Does anyone know where it goes and what it is for? Could it be related to a misfire? An option my car doesn't have, For digital dash cars only, etc.?.
Thanks for any help.
Last edited by 85-300ZX2+2; 08-06-2022 at 01:52 PM.
Please see the Mystery wire picture at the bottom.
Noob's to the 300zx's as we bought a nice low mileage 85 non turbo, base, non digital dash 300zx 2+2 for my son about two months ago with 83k miles on it. Auto transmission. Been awesome until now after about 1k miles for us.
We have some maintenance records for the car with the timing belt changed at a local Nissan dealership back in 2015 and it now has 13k miles on that timing belt. Also have records the distributor was replaced 5 years ago and the car has a history of rear brake issues and warm start problems. It hasn't been modified in any way that we can tell and the previous owner was not aware of any changes either.
I downloaded the factory service manual already and it helped me fix the rear brake noise we were having and I have read quite a few of the posts here and cannot find an answer to this new issue and got confused.
The car ran great and had a very minimal uneven idle sometimes like a possible misfire. Not surging or changing RPM's, just an intermittent very light idle shake when hot. As we didn't know the plug history we decided to change them.
It had NGK wires and plugs and from searching it appears they were oem replacement parts along the way. The plugs in it were NGK-BCPR6ES-11 like the owner's manual indicated and all looked good and firing cleanly upon inspection.
The number one plug wire was so fused/stuck on the plug it tore upon removal. Went and had to get an aftermarket plug wire set as no auto parts store here had the NGK wire set in stock and couldn't get one for 4-5 days.
I needed the car before then so went and installed new NGK-BCPR6ES-11's and the aftermarket plug wire set. It ran terrible after this. I noticed a crack in the distributor near the number 2 terminal so went and got an aftermarket cap and rotor from CARQUEST.
No change with the new the cap and rotor and after sitting overnight it idles even rougher than yesterday. RPM's hold steady at 6-700 but the car shakes bad with a definite misfire(s) now. This morning I put back in the old NGK wires except the torn # 1, left the aftermarket #1 wire and left the new plugs in it. No change. Unfortunately I already threw out the old plugs to try them back in the car as I have never had a bad plug issue before.
I thought I had it tracked down to # 6 cylinder this morning and a bad plug as it ran no worse at idle with the #6 plug wire disconnected but testing the new sparkplug out of the car with a digital meter seemed to show it was ok. There was a noticeable change in the idle when I disconnected the other plug wires individually but not with # 6 disconnected.
I know brand new plugs and wires can have issues sometimes and I have another set of NGK plugs and NGK wires now on order after not wanting to wait 4-5 days, and now the car is out of commission for 7-10. Big sigh....
I am out of ideas. Any ideas would be greatly appreciated. I know we violated the first rule of avoiding a pain in the butt being "If it isn't broken don't fix it" and now I really have to fix more.
Fixing your kid's cars can age you fast.
I noticed this unconnected orange mystery wire from the wiring loom near the Idle up solenoid where I was working between #2 and #4 plug wires. I noticed it when I started and don't think I knocked it loose. It has a female connector and looks like it slides on over a post type connection. It only has about 8 inches of play and comes out of the wiring loom for the idle up solenoid so it should go somewhere over on this left side of the intake plenum as shown. Does anyone know where it goes and what it is for? Could it be related to a misfire? An option my car doesn't have, For digital dash cars only, etc.?.
Thanks for any help.
Did you gap the plugs? Are you sure the plug wire boots are plugged on the spark plug properly? Are the wires on wrong? Did you crack a plug? Are the plugs on tight?
08-06-2022, 01:29 PM
