Rough Idle

[Ransome]

My '92 300ZX won't idle correctly. It idles low (500-1000 rpm), but when geting on the gas it runs fine after about 1200rpm. I read an article on here explaining how to put the ecu in diagnostic mode and the ecu is not detecting any problems. What problems could cause the car to idle rough but not be detected by the ecu and set off no warning lights?

[vitaminZ]

Have you considered installing a grounding kit on your 300ZX?

is there a write up on installing this and where do i get kits!!

[CrazedZ32Owner]

i had the same problem on my TT.... just changed the filter and cleaned the MAF(dirty as a motherf*cker) did wonders and it was like 20 bucks at autozone....


the one time they actually HELPED me, im not saying thats your problem but start at the cheapest thing you can do and work your way up unless you KNOW whats wrong or someone tells you what to check

[Ransome]

i had the same problem on my TT.... just changed the filter and cleaned the MAF(dirty as a motherf*cker) did wonders and it was like 20 bucks at autozone....

Where exactly is the Mass Airflow? I tried checking a bunch of plugs and wires and vacuum lines today to make sure everything was tight but I'm not exactly sure where the MAF is located. And THANKS for the reply!

[robomatic12]

MAF sensor located underneath the center nose panel held in place with two 10mm bolts. Pop the hood to access the bolts.

Now I don't think any of the above will fix your problem. Most likely you either have a cylinder misfiring at idle or the IACV is clogged/not working. Does the engine rock back and forth visually? Perform a power balance test by pulling the coil pack connectors off one at a time, each one should drop the idle a little bit and go back up when you plug it back in. If one does not respond, it's not firing.

As for the IACV, you either take it off and clean it out using carb cleaner and lubricating with WD40, replace it, or try to clean it with it on the Z. You can remove one of the air supply hoses (straight one inbetween IACV and air regulator) on the left hand side of the engine feeding the IACV and spray WD40 with the engine running. Search for a guide on how to do it if you want more info. Then after cleaning it properly adjust the idle RPMS. Unplug the IACV and set idle rpms with idle screw, then replug the IACV.

[Ransome]

Yes you can see it rock back and forth. I'm definitely going to try all of these things. Thanks for all the replies!

[robomatic12]

Yep you've probably got a dead cylinder. Figure out which one it is, then we can verify if it isn't getting fuel or spark and go from there.

BTW Forget any ground-net stuff for your problem.

[Ransome]

I finally had some time to mess with the z again. After reading some posts on here about pulling the coil packs while it was running, I definitely detected one cylinder with no change in idle after pulling the pack. I started with that injector and it would not give the correct ohm reading. So I started doing each injector and only had 1 injector that actually gave a reading between 12-14 ohms. So it seems like some of the injectors haven't failed completely but are on the way.
So today I got a complete fuel rail with the new style injectors and the harness from a z shop, but I have a few questions:
1) Each injector had the exact same reading of 11.3 ohms. Is that correct for the new style injectors?

2) I know that I definitely have to pull the plenum to get the complete rail installed, but will the harness plug right in to the existing harness on my '92? My guess is no, so what will I need to do to get the injectors working.

It seems like if you plan on keeping the car for some time that the new style injectors are the way to go. So now that I have them, what next?