Low idle/misfiring after rotor/cap replacement

[s13satch]

A few days ago I decided it was probably time to replace my cap and rotor on my '91 240SX. The car had 119,XXX miles and I had installed an MSD ignition last year around this time. I figured the OE pieces would most likely be shot at this mileage, especially with using the MSD for the last 6K.

It turns out that I was right. My rotor was so burnt that I could not believe the ignition was actually working (see pic). The cap wasn’t as bad, but pretty close.

I bought a new rotor and cap through Nissan and was hoping that the parts would make the car run a lot better. I drove the car around for 2 days and was kind of surprised that I didn’t notice a difference in power, fuel economy, or throttle response. On the 3rd day the car sat. On the 4th day I went for a drive for about 20 minutes. I parked the car at this point and went into a bar to see if any of my friends were there. Not seeing anyone, I went back out to the parking lot and got in my car to leave. When I started the car it was only running on 3 cylinders. This lasted for about a minute. Then, for my entire drive home, the idle was either sporadic, or at a steady 500 rpm, but it did not misfire again.

The next morning I briefly looked around for any obvious issues. The cap was still on tight as were the spark plug wires. So, I started the car and let it warm up. Everything seemed fine so I shut the car off. I did not drive the car until the next morning. It started fine so I left to go run an errand. The car had fully warmed up by the time I had got to the store and there were no signs of the idle/misfire issue from 2 days earlier. However, when I went to start my car to leave, it started on 3 cylinders again. Just as the car had done 2 nights prior, it misfired briefly followed by a sporadic/low idle for the rest of the drive home.

When I got home I decided to do a little more thorough search. Once again I started by checking that the cap and plugs wires were tight. I then proceeded to check the plugs (replaced with the MSD install last year). Next, I checked the connector to my MAF (dirt in it had caused idle issues in the past). Next, I check the ground wires for the motor. Finally, I checked my wiring for the MSD unit to insure that all the connectors were still connected.

My search found that everything appears to be alright. Before I break out the service manual and my multi-meter (or just take it to the shop) I was wondering if anyone has any suggestions for me? Or if anyone had experienced similar problems?

Thanks.

[Acecool]

Look by the fuel rail, closer to the cabin.. Take the 2 bolts off that little thing with the tubes coming from it.. The line on the bottom of mine was FUBAR, I cut the ends off it, replaced it and replaced my injectors WITH NEW INJECTORS ($40 USD off ebay, rebuilt injectors with 40k)

Fixed my idle, hesitation, stumble and backfire

[rogoman]

Have you determined which cylinder is misfiring? If it's always the same cylinder, now you have a starting point to determine if it's ignition or fuel.

If ignition, a possible defect in the distributor cap. If you still have the old cap, reinstall it to see if the problem goes away.

If fuel, the injector may be dirty or sticking. Run some injection cleaner through the system.

[s13satch]

I do not know which cylinder was misfiring. Of course, the car runs fine while sitting in my driveway which makes diag all the easier.

I no longer have the old cap because when I removed the cap, two of the four terminals chipped off when I touched them. I therefore didn't see a reason to keep the damaged part.