i have had my car for about 6 months now. about two months ago i noticed it started to idle rough and it was dropping to about 500rpms and shaking, but never stalled though. i took it to the dealer and had a full tune up done. and it is still doing the same thing it did before. it is smooth as can be if i have the a/c or defrosters on. any suggestions on what is wrong or how to fix it is appreciated. thanks

 

I had a similar problem and it was a faulty injector.

 

Mine does the same thing. It idles at 500rpms. Do you think a bottle of fuel injector cleaner might help this problem?

 

Doubtful! The resistance is probably not right. Each injector should measure 10-14 ohms. If it's too high, you must replace them. No fuel injector cleaner can fix that.

 

thanks for the tips, but one more thing. Where can i get new injectors, and for how much? Also how hard are they to install?

 

yet. That is a very expensive proposition and RARELY is a bad injector at fault on these cars. However, the resistance of each injector can be tested pretty easy if you have a multimeter. Just pull each injector clip and then check the resistance between the two prongs on the injector. Should read 10-14 ohms. If not, then you are in trouble and we can go from there.

But, more often than not, injectors themselves are not the cause. What did the dealership do at your "full tune up"?
I assume the plugs were changed and gapped correctly? Fuel filter changed? Perhaps injector cleaner ran through the system? Did they attempt to set the idle? Does it idle too low all the time when it is warm? or is this just an occasional thing? Does the idle hunt at all (go up and down)?
The best thing to do to start is when you check the resistance of each injector, take a piece of sandpaper and clean the injector and the harness very well. Also check the condition of each harness, look for exposed wire, etc. The harnesses themselves get into very bad shape on the Z just because of the extreme engine temps. Also clean all the connections on your TPS, CAS, and PTU, and each coil pack . If you dont know what these are, email me. Did the Nissan dealer run a Consult during your tune up?

FYI I've seen it happen multiple times where a mechanic will tell a Z owner they have a bad injector. Why? Because the book factors in pulling the plenum in injector replacement. That is an easy $1000 for them. Individual injectors can be changed without pulling the plenum, all you need is a dremel. These mechanics also never bothered to check and clean the connections until after the new injector was put in. Oh, its magic...how about that, the car runs great now. Why charge them a few $$ to clean a connection when I can make a $1000?
Hang in there, cover ALL your bases before you go for a major op like injector replacement.

91 300ZX TT. Lots of mods, check Rides under my Profile if you are interested.

 

I'm sorry, but faulty injectors are EXTREMELY COMMON on 300ZX's. In fact, I had 3 go out on my 90TT with only 14K miles on the car. They go out all the time. You can ask anyone that works on Z's and they'll all tell you the same thing. Ohm up the injectors because I'll bet there's at least one bad one. Nobody said to replace them if they don't need to be replaced. They can be ohmed up at the injector itself or at the ECU. If you don't think it's common, go to twinturbo.net and do a search. It's one of the most common things to go out on Z's.

And what a difference it makes when they're all working properly! :-)

 

All I know is I have now had two Z32s and done just about any and everything you can do to the car. I can pull the motor in my sleep now... I've NEVER had a bad injector. I've had 2 friends who were diagnosed bad injector, I cleaned or changed an injector harness and they worked just great. I've been a member on twinturbo.net since 99 and managed to rack up a stage VI addiction (though admittedly I haven't wasted as much time there as you have ) The point I was trying to make is you check the easy things first, and cover all your bases before you move on to the things that cost real $$$. Someone tells me I have a bad injector, big deal. I'll have the plenum off, it replaced, and it back on in under 3 hours. For most people though, if you tell them that right up front and they DONT do their own work, they can easily run to a mechanic and wind up spending lots of $$$ on something that will not necessarily fix their problem. Just didn't want to discourage the guy right up front, thats all.


91 300ZX TT. Lots of mods, check Rides under my Profile if you are interested.

 

I agree...I wasn't saying to go out and buy the injectors yet. :-) Just ohm them up because I'm 99% sure that at least one is bad (and it's easy to ohm them up). Once the resistance is off, there's no fuel injector cleaner in the world that will work. Above 14 ohms, it's time to replace. This is what I experienced with my 90TT, what I've heard on tt.net since the tt.com days, and what Chris at Ultimate Z told me. It is a very prevalent problem without question. But like I said, don't run out and buy them. ;-) Just ohm them up!

 

sigh...maybe someday. But just wanted to say you have a damn nice looking Z.

91 300ZX TT. Lots of mods, check Rides under my Profile if you are interested.

 

Why thank you! :-)