NA z32 1990 JDM bizzare idle, slight misfire and more

[Xz003nassin]

My Z hasn't been running very well lately. Symptoms are: bizarre and finicky idle conditions (cold start around 1500 sometimes even 2000 rpm, then when warmed up it usually settles to around 1000 when idling but ocasionally gets "stuck" at around 1500), low end power loss and slight hesitation, rough running in first gear (a little jerky, bogs down a bit), noticeable miss- when idling it vibrates and isnt as smooth as it should be. Misfire is only noticeable during idle and seems to have a "dead spot" at Around 2000rpms. When cruising at 2000rpms (not hard acceleration) it runs rough and kinda choppy. Any other rpms it runs smooth and fine, hard acceleration it runs fine. It still has lots of pull in the higher rpms, it just ssems to have a distinct bump at 2000. Another thing i should note is that the left exhaust tip has more carbon build up then the right, and when i pulled the plugs, the ones on cyl 4 and 6 were pretty black with build up, go figure. I just replaced the plugs before i did this, so plugs are fine: yes theyre ngks. Coils all ohmed alright and all seem to work. I checked the codes and got a 55, so all good there. Also checked the o2s, and they tested fine. I Cleaned injector connectors, reset the throttle body sensor, tried messing with the aicv a while ago but thats defs not gona fix much. I just did an oil change, new fuel filter, new air filter ( old one was disgusting and filled with crap). I thought that did someting at first but i guess not

Not really sure what to do now besides start replacing coils and injectors. Maybe a wiring harness. The car is still driveable but its annoying and a shame that the z isnt running like it should. Plus im getting terrible mileage, i put only 94 in it and im not made of money....

Any tips and suggestions would be appreciated, thanks!

[nissanfreak12]

First thing to check for is a vacuum leak
Next green corrosion on the connectors
Then Check each injector and make sure they ohm between 10-14, anything more, they are bad
Next full tune up.

Let us know what you find! The first three are easy and fairly cheap as long as you have all the tools. My money is on either vac leak or bad injectors.

You also stated it was a 1990, do you have the new style PTU? All black is the new style. If it has silver fins, thats the old style.

[Xz003nassin]

Alright thanks, i'll look into those. Mine has silver fins so old style.

[nissanfreak12]

Change the PTU, those have been known to cause a lot of issues. That is why they updated them. Still check everything else I listed.

[Xz003nassin]

Alright so im currently in the proccess of installing new injectors- got the new style set of six w/ new connectors and adaptor kit. Hopefully that solves the problem, or at least the rough running. Is it even possible for a bad injector or two to cause that finicky of an idle?

[nissanfreak12]

It will, but did you test the injectors first? If they read between 10-14 ohms, you should be good.

Have you done a power balance test? Simply unplug one coil at a time and if there is no change in idle, that is the cylinder with the problem.

Did you ever do a Leak test? This will get you very poor mileage and idle issues.

It sounds like you didnt even check anything suggested and just decided to throw money at it. Granted, new style injectors are much better than the old style. It could fix your problem, but doing the simple test will help not throw parts at the problem.

To answer your question, yes, a bad injector can cause bad idle, or idle issues.

[Xz003nassin]

I did ohm the injectors- a couple were out of spec. Didn't mention that before oops. And also used a mechanic stethoscope to check for the clicking. One of them wasnt clicking at all, so i decided to go and replace them all. Gona replace some hoses around the bay while the plenums off, some look really tired and cracked.

Should have it together again in a few days, so ill see what happens. If its still acting up ill do a leak test next. Probably should have done it before i dismantled it, ha. But oh well, its my first car so you could say im definately a newbie. Thanks for the feedback

[nissanfreak12]

Replacing all with new style injectors is a smart move, especially if two were out of spec.

Doing a leak test after you get it back together is also a good idea, unless it runs better. But I would still do a leak test, just to make sure.

[Xz003nassin]

So after replacing injectors+connectors, coolant bypass, some vaacum line replacing and ajdusting the timing, my car is finally running alot better. Runs smooth now, seems to be on all six. Now, however, it doesnt wana hold its idle. (Stalls when trying to idle) and could use a little more low end power too... I realize na's arent crazy fast but it feels like it could put out a little more. Anyways, i might do some very slight timing ajdustment tomorrow and try to figure out this idling problem. In the meantime im happy its running nicer. Had to do the water pump previously also so there was a lot of time spent in my garage, stoked its on the road again. Gotta repaint the hood after i sort out these couple things and itll be good to go! Black hood or body color...hmmm.

[Xz003nassin]

Update here: the car is still acting the same, with a hunting idle. Im thinking its a sensor. Most of the time it hunts, sometimes it stays stable but not usually. Also its clearly missing some low end power and bogging when im starting from a stop. If anyone knows what it could be, any input would be great. So far ive cleaned the maf connector and the tps sensor connector, iacv seems fine too.

[Xz003nassin]

Just checked the codes again, now its giving me 34 and 12. MAF and knock sensor. s***....

[Xz003nassin]

Update: it was the maf. Car runs well now.

[dzap]

Update: it was the maf. Car runs well now.

Did you clean the MAF or did you completely replace it with a new/different one?