N/A idle issue help

[method2madness]

Wussup guys, I haven't really posted much on here about my Z. I have a 1990 NA 2+2 and I'm having issues with idling. Everytime I put the car into any gear the car revs up to about 3000rpms and goes down as soon as I take it out of gear. The car does this when driving and shifting through the gears. It's really become annoying especially when downshifting and coming to a stop. Also when the car rolls a little the rpm revs up to 3000 on its own A friend of mine told me I may have to cap a vaccum or leak on the transmission to solve the problem. But I'm wondering if this problem is because of the the harness swap I did from a '95 z. Any suggestions????

[method2madness]

Anyone???

[zcar93na]

The only thing I can think of would be a small vacuum leak, a large one would stall the car out. There's no vacuum lines going to the transmission that I know of. Mine revs up to about 2k if I start driving it before it's to running temp. It could be a sensor but I'm not sure what it could be. The harness swap could be some of your problem. Why'd you put a '95 harness in a '90 model?

[Recian]

that would be a lot of issue. not to mention 95 is obd2 and 90 is obd1. Plus these harnesses are finickey and very fragile due to age and the bends they make on the back of the engine I wouldn't be surprised if you have a bad harness. My car was doing the same here recently so I've studied up on idle issues. First check for any leaks. If you have none or after repairing them then you can adjust the idle with a screw on the IACV at the back of the driver side intake. The FSM says to adjust TPS to spec before doing that, basically saving the screw as a last resort but it is possible it's been messed with. If you can screw it all the way in and car doesn't die you have a vacuum leak. Also check for dirty throttle bodies. My car used to idle at 2200 cold. Couldn't idle through the neighborhood when it was cold. I've tuned that screw back and it idles at 750, 650 with lights on and 900 with a/c on. 1700 when cold.
Mine likes to stay at 2200 after you take it out of gear and coast but it's not as bad now and drops soon after it realizes you're slowing down. May need to look into the IAC and see if it's not clogged or stuck open too. These cars use a 2 valve system in the IAC and it's a bit more complicated than it needs to be honestly.

[method2madness]

that would be a lot of issue. not to mention 95 is obd2 and 90 is obd1. Plus these harnesses are finickey and very fragile due to age and the bends they make on the back of the engine I wouldn't be surprised if you have a bad harness. My car was doing the same here recently so I've studied up on idle issues. First check for any leaks. If you have none or after repairing them then you can adjust the idle with a screw on the IACV at the back of the driver side intake. The FSM says to adjust TPS to spec before doing that, basically saving the screw as a last resort but it is possible it's been messed with. If you can screw it all the way in and car doesn't die you have a vacuum leak. Also check for dirty throttle bodies. My car used to idle at 2200 cold. Couldn't idle through the neighborhood when it was cold. I've tuned that screw back and it idles at 750, 650 with lights on and 900 with a/c on. 1700 when cold.
Mine likes to stay at 2200 after you take it out of gear and coast but it's not as bad now and drops soon after it realizes you're slowing down. May need to look into the IAC and see if it's not clogged or stuck open too. These cars use a 2 valve system in the IAC and it's a bit more complicated than it needs to be honestly.

I did the swap bc my old one was shot like the coil pack and some injector connectors. So I used one from my buddy's old z that he did a tt swap on. I'm going to check the iac and check the tps as well since I retrofitted that too.

[Z-owned]

that would be a lot of issue. not to mention 95 is obd2 and 90 is obd1. Plus these harnesses are finickey and very fragile due to age and the bends they make on the back of the engine I wouldn't be surprised if you have a bad harness.

To correct you 96 is when the switch to obd2 happened not 95. However the op hasn't stated manual or auto for his as well as the car the harness came from, but just cause it's a different year doesn't mean it won't work. either way though the the 95 has the new style connections for the injectors, cas. Etc so I feel some info is missing to help further diagnose the issue.

[Z-owned]

Bernie explains the engine harness compatibility pretty good here.

http://www.yugobernie.com/harness.html

[method2madness]

that would be a lot of issue. not to mention 95 is obd2 and 90 is obd1. Plus these harnesses are finickey and very fragile due to age and the bends they make on the back of the engine I wouldn't be surprised if you have a bad harness.

To correct you 96 is when the switch to obd2 happened not 95. However the op hasn't stated manual or auto for his as well as the car the harness came from, but just cause it's a different year doesn't mean it won't work. either way though the the 95 has the new style connections for the injectors, cas. Etc so I feel some info is missing to help further diagnose the issue.

My car is a '90 5 speed and the harness came from a 95 auto. I also did the new injectors to old style fuel rail conversion before realizing some of the wires were f*cked. so instead of trying to trace all of them i just used my boy's spare harness to see if it would work. I completely forgot we used the auto ecu. Now im pretty certain thats the culprit. I disregarded that since the car has been running fine aside from the idle issue. I just need a 5 speed ecu now.

[DCaff300ZX]

I believe that I was told by my 5spd swap guy that the auto ECU can be used with the 5 speed swap, as was the case with my NA, but not the other way around so you should be OK with the 95 auto ECU. My NA also went through the idle issue thing years ago, and the culprit was hoses and IAC cleaning, luckily. Spraying WD-40 into it a few times fixed it, unlike currently with my TT.
I'd concentrate on the IAC and throttle body cleaning first, then as I am currently doing (unsuccessfully so far as well) follow the FSM tests of the related controllers and such looking for the issue. I've heard and read of a lot of IAC issues related to idle and as stated by another above, the system is overly complicated and therefore a PITA to deal with without instructions from the FSM.

[method2madness]

I believe that I was told by my 5spd swap guy that the auto ECU can be used with the 5 speed swap, as was the case with my NA, but not the other way around so you should be OK with the 95 auto ECU. My NA also went through the idle issue thing years ago, and the culprit was hoses and IAC cleaning, luckily. Spraying WD-40 into it a few times fixed it, unlike currently with my TT.
I'd concentrate on the IAC and throttle body cleaning first, then as I am currently doing (unsuccessfully so far as well) follow the FSM tests of the related controllers and such looking for the issue. I've heard and read of a lot of IAC issues related to idle and as stated by another above, the system is overly complicated and therefore a PITA to deal with without instructions from the FSM.

I'm definitely going to do that this weekend. and also post some pics of my car on the forum of how she's coming together.

[DCaff300ZX]

Another thing to look at is where I will be looking this weekend, among other things- at the connectors to the entire IACV unit as apparently as with many of the other connectors they are easily corroded and can cause issues. I'm SERIOUSLY hoping this is my problem after about 3 months chasing BS and never fixing the problem while other things work better.