car loops idle up and down when gas is let go

[rb25crazy]

hi guys

i'm stuck as to why my 97 s14 does this, it only started today.

happens more often when it is cold too

what happens is, is that the cars idle goes up and down from 1000 to 500rpms when at a stop sign. If i rev it up full throttle the problems "goes away" sometimes for a bit but then comes back later again, having another loopy idle that just goes up and down.

Another thing I notice is if i am driving like at any speed 25mph for example and i let go of the gas, the idle goes up and down and loops till I step on the gas again.

Sometimes, when i step on the gas it stalls for a little bit before it goes also....

Please help, to check what and how to check it. I'd like to get this done asap with your guidance wise people!

thanks a bunch

[Tampwns]

Vacuum leak

[rb25crazy]

any ideas where to look? and how to tell if there is vaccum leak?

[b4l]

soap and water were you have your vacuum lines at if you see bubbles then theres your problem

[rb25crazy]

great idea thanks man! but is hte soap dangerous for the electrical stuff?

[rb25crazy]

not that i am going to try to put it on the electrical stuff, but if it does fall on it, it wont destroy or short it irght

[b4l]

put it on the ends of the hoses only try to avoid wires use a spray bottle

[mxexux]

I don't think soapy water will find a vacuum leak considering that it would just get sucked in instead of making bubbles.

Another possible cause to this is a dirty IAC-V. It is bolted onto the back if the intake mani and kind of a pain to get out, but cleaning it may solve your issue.

[Frank_Jaeger]

Start your car.
Spray engine starter fluid around your bay.
If you hear the idle rise or smooth out, then you're near a leak.

Check around the intake manifold and brake booster. Especially the IM.

EDIT: If you get light headed with the starting fluid then take it easy on the spraying. Diethyl ether's a lot of fun but the other chemicals in starting fluid cause immediate brain damage.

[rb25crazy]

I don't think soapy water will find a vacuum leak considering that it would just get sucked in instead of making bubbles.

Another possible cause to this is a dirty IAC-V. It is bolted onto the back if the intake mani and kind of a pain to get out, but cleaning it may solve your issue.


hmm dirty iac-v..... stupid q but dhow do u clean it? is it something that i can take out?

[iRideFBMSR20det]

Check the 2 wire engine coolant temp sensor

[mxexux]

hmm dirty iac-v..... stupid q but dhow do u clean it? is it something that i can take out?


Yes, you can take it out, but its not that easy. Check this out for more info: IACV AAC cleaning and testing tutorial : Nissan Online Mechanic (http://forums.nicoclub.com/iacv-aac-cleaning-and-testing-tutorial-t251133.html)

It pertains to an S13 KA24DE, but its similar enough so you get the idea.
Good luck:s101:

[mxexux]

Check the 2 wire engine coolant temp sensor

Yes, try this first as it is easier than the IAC-V.

This brings up a question for the OP -- Is there a check engine light?

[rb25crazy]

Yes, try this first as it is easier than the IAC-V.

This brings up a question for the OP -- Is there a check engine light?

no check engine lights

and how do i check the coolant 2 wire sensor? silly question

[project925]

Idle Air Control Valve. Take it off and spray it with brake clean then WD-40. The brake clean will clean up the carbon and the WD-40 will loosen the stuck spring.
you also want to replace your PCV valve because that's what's letting carbon into your idle air control valve

[mxexux]

Here you go...
http://i130.photobucket.com/albums/p260/positron32/IMG_1611.jpg

There are 2 temp sensors. The one with one wire is for the temp gauge on the cluster. The one with 2 wires goes to the ECU and uses it to adjust fuel trim properly. Just make sure is has a good connection. You could even spray the terminals with brake clean.

I am sorta doubting this because if there is a problem here, normally the CEL would be triggered. But, I've seen stranger things happen.

[Lalaland]

Could be a bad Lambda sensor. I've experienced this exact behaviour in various cars with a busted oxygen sensor. Not always triggering the Check Engine light either. Could be worth checking if nothing else does the trick.

[kouki-gymkhana]

I'm sorry if you mentioned it but what motor do you have in your 97 s14, given the fact that your S/N is "rb25crazy"? If it's an RB25, then I suggest you remove and clean the IACV, change the ECU coolant temp sensor, and check for vacuum leaks. These motors are NOTORIOUS for this kind of behavior.

[rb25crazy]

Here you go...
http://i130.photobucket.com/albums/p260/positron32/IMG_1611.jpg

There are 2 temp sensors. The one with one wire is for the temp gauge on the cluster. The one with 2 wires goes to the ECU and uses it to adjust fuel trim properly. Just make sure is has a good connection. You could even spray the terminals with brake clean.

I am sorta doubting this because if there is a problem here, normally the CEL would be triggered. But, I've seen stranger things happen.

great thank you sir, I have to ask though... i am a retard how do you check for a good connection? i have a volt meter... I appreciate the help regardless!

[rb25crazy]

Could be a bad Lambda sensor. I've experienced this exact behaviour in various cars with a busted oxygen sensor. Not always triggering the Check Engine light either. Could be worth checking if nothing else does the trick.

bad lambda sensor? is that the o2 sensor? i changed mine back like 10k miles ago. im assuming its still good unless... i got unlucky with a new one.

[rb25crazy]

I'm sorry if you mentioned it but what motor do you have in your 97 s14, given the fact that your S/N is "rb25crazy"? If it's an RB25, then I suggest you remove and clean the IACV, change the ECU coolant temp sensor, and check for vacuum leaks. These motors are NOTORIOUS for this kind of behavior.


yes sir, i have the ka24de, the rb25crazy is just my handle... no worries, I can see how you got confused.

[Lalaland]

bad lambda sensor? is that the o2 sensor? i changed mine back like 10k miles ago. im assuming its still good unless... i got unlucky with a new one.

Yes, the O2 sensor :) But since you've got a fairly new one i probably would listen to these other guys, regarding the vacuum leaks an so on. You never know with sensors but i doubt you are that unlucky.

For the electrical tests i would set your multimeter to Ohm, and measure your temperature sensor directly without the connector in, note the reading on your meter, reconnect the plug. Then i would measure the same thing on your main connector on ECU, measuring between the signal wire and ground on ECU, not the chassis or elsewhere. The value should not change notably. If it does you have a bad wire or connector somewhere in between.

Probably not the most helpful information, but systematic troubleshooting is the route to go.