i'm idling around 1500 on average with no heat or accesories. when i start the car, it hangs around 2200 for a bit. the high idle issue has been discussed to death, so the purpose of this thread is to draw a connection, if possible, between high idle and surging. this is where, in 2 second intervals, the idle does a strait drop, then rises back up. at the bottom of the drop, it might get down to 1000, then back up to 1500, every 2 seconds.

i've seen it happen on many jap cars, but i still don't know exactly how to fix it. is there a specific vacum line or sensor that may do it? i sure would love to get the idle down and steady. coolant temp sensor has been replaced.

 

and WTF is this? that fuel line has been plugged since i got the car and i can't find anywhere that it might go!

 

and maybe high idle hasn't been discussed to death. i just did an advinced searc for "high idle" sorted by relavancy and didn't really find anything helpfull near the top of the list

 

Does your car have an o2 sensor in it?

 

2 of them. and they havn't been replaced. would this cause high idle?

 

https://www.zdriver.com/forums/showp...6&postcount=17

 

and i am not aware of a fuel line below the plenum

 

its prolly a coolant line. to heat the TB's

 

i assumed it's a fuel line, i shouldn't have described it as so. i thought is was a fuel evaporatory line or something because it has the same kind of cover with holes in it as the rest of the fuel lines. and thanks a lot for the link

 

Its very possible your o2 sensor went bad and that can screw up all sorts of things related to performance.

 

i'll do the ECU test on them. thanks for the advise. and by reading through that most excellent link, i am looking toward the o2 sensors (which would be bad because based on the thread that i read, if the o2 sensors are causing high idle then you are running lean... i hope that didn't mess up my nice new valves...).
i'm also looking at MAF. i had read previously that this couldn't affect idle, but this guy said he cleaned that and his idle went from 1500 to 800 instantly

 

you should run the entire ECU test. i think theres 2 different test modes for codes. you got the write-up yes?

 

yea i've done the rest of the test. all good exept the knock sensor

 

That hose is simply a vacuum hose port... I believe that one connects to the carbon canister. Most people (including myself) eliminate the hardline entirely (for plenum pull simplicity) and just run a rubber vacuum line in its place.

And your idle problems are probably related to either the TPS or the IACV (more like the IACV).

 

have you tried adjusting your idle screw?

 

yea i've done the rest of the test. i do it reguarly actually. all good exept the knock sensor. resistors are sitting in my center console. come to think of it, i've done the o2 sensor part before and the light didn't show at all... i though i was doing it wrong but maybe they are just bad.

 

that message submitted way late or something. but no, i havn't messed with the idle screw. i figured that is just masking the problem and might make it run worse in the long run. and thanks for the advise. i'll try to find the carbon canister and all. as for the TPS, i tested it thoroughly this weekend and found that the contacts (connector on front) are working fine but the pantametor is not. very little voltage all around. it seemed to me that if the contacts were working then it wouldn't affect idle. i have read that the IACV could be a problem, but it wasn't too high on my list. i'll move it up. thanks a lot!

 

O2 sensors can be related to idle. I'd definitely agree with the IACV as I've discovered with my 280ZX, these things can go bad, but still work. For a 300ZX the car may be able to pick up a different signal from it saying that it's working, but the diaphragm inside these can wear out and still allow extra air to pass by.

 

ok thanks. looks like i'm going to be spending some money at any rate. but no one has any idea on the surging? that one's actually embarassing when i pull into school lol.

 

that is correct. it really wont even do anything if you change the idle screw.

IACV is the source of many idle probems. and possibly the air regulator

maybe look into getting a new thermostat if you havent yet as well

 

ok i'll post back after i test the IACV. thanks for all the advise.

 

i had a very sudden recolection of reading somewhere else about how the EGR valve being stuck or disfunctional could cause the idle to pulse or surge. but i've only ever seen it that one time. any one else heard of this? i certainly don't want to get into that job without being positive that that is the problem.

 

sorry for mah ignorance, but is there an idle control motor? when those go bad there is idle surge.

 

if your ecu didnt give you a fault code for the EGR, then i wouldnt worry about that yet

 

new info on the probem. it always surges when the heat is on, and it will stop when i turn the heat off. but after driving some more with the heat off, it will start again next time i stop. this problem is from hell