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techninja15

When idle, RPM will drop. Thanks for the help!

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Hello,

 

Hope I'm putting this post in the right section. I tried searching for idle issues in the forums, but the ones posted seemed different from mine and was wondering if you guys could help. Thanks in advance...

 

 

 

When I start my 97 180sx SR20DE in the morning, it idles perfectly fine while I let it warm up.

 

However during the afternoon or even after "spirited driving" when I am at a stop sign or light and just in neutral, my RPM will drop and then raise again and drop and then raise again. I just changed the spark plugs to iridium NGK hoping that would fix my idling issues, but so far its still there.

 

I also tried unscrewing what I was told was the "AAC valve" (a screw under the plenum) and spraying it with some carb cleaner. It seemed to work for a bit, but later on it comes back.

 

 

On the way to work I was driving pretty fast and for the first time ever my RPM when in idle dropped dangerously close to shutting my car off. Any help would really be appreciated.

 

Thanks

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When I start my 97 180sx SR20DE in the morning, it idles perfectly fine while I let it warm up.

 

However during the afternoon or even after "spirited driving" when I am at a stop sign or light and just in neutral, my RPM will drop and then raise again and drop and then raise again. I just changed the spark plugs to iridium NGK hoping that would fix my idling issues, but so far its still there.

 

I also tried unscrewing what I was told was the "AAC valve" (a screw under the plenum) and spraying it with some carb cleaner. It seemed to work for a bit, but later on it comes back.

The first part you wrote sounds like IVAC which you cleaned. the last part....

On the way to work I was driving pretty fast and for the first time ever my RPM when in idle dropped dangerously close to shutting my car off. Any help would really be appreciated.

When your driving & changing gears does the rpm drop dangerously low? & at idle goes up & down.

 

If so its your coil packs &/or the ignitor. start with the coil packs you can get them tested or buy new OEM or spitfire ones

(i personaly dont recommend any other brands)

~ failing that its the CAS but thats unlikely & not wise as a first choice, as it costs alot & people who have had the same probliem & been recommended to do the CAS have found it doesn't

help.

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Thanks for the advice, I'll be sure to get my coils tested and post the results. My rpm dropping issues only occur when I'm stopped, and they are most severe after driving fast. If I were to drive normally, it drops, but not dangerously low to kill the power. But lets say if I were to over take someone and speed past him, the next red light my car would drop its RPM and make my car shudder as if it were going to shut off. Thanks again for the help.

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Unplug your AFM and see if that changes anything - you may need to unscrew and clean the actual sensor.

 

have you checked your TPS voltage? it should be reading 0.45 - 0.50 with the engine off and on reds only

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I'm guessing DEs have an oxygen sensor similar to DETs and it may have failed. A failed oxygen sensor will clog up your IACV with carbon deposits and cause the problem you have described.

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Okay so I'm gonna try to check my TPS and also my O2 sensor. Hopefully its just a little cleaning. Drift competition this Sunday here in Japan that I don't wanna miss >.< Thanks again guys/girls

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I'm guessing DEs have an oxygen sensor similar to DETs and it may have failed. A failed oxygen sensor will clog up your IACV with carbon deposits and cause the problem you have described.

how does a bad 02 sensor clog up the iacv wouldn't it just cause it to run lean or rich

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Exact same issue on my rb20det

 

Didn't wanna start a new thread but will give year options a go

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I would suspect the iacv as the culprit, given you sprayed carby cleaner in the screw hole, it fixed it for awhile, then it came back. I would take the whole iacv unit off and clean it properly.

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I'm guessing DEs have an oxygen sensor similar to DETs and it may have failed. A failed oxygen sensor will clog up your IACV with carbon deposits and cause the problem you have described.

how does a bad 02 sensor clog up the iacv wouldn't it just cause it to run lean or rich

 

Yes the car will run richer, and with the richer mixture you get the carbon buildup. As I understand it the O2 sensor only comes into play after the car's reached operating temp where it adjusts the idle characteristics of the engine to suit. If it's not working the ECU doesn't get this signal. A stuffed sensor won't bring up a fault code either, only if the circuit (wiring) is physically broken.

 

It'd be something I'd be looking at anyway by what you've described.

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yeah i know what your saying but isn't carbon a product of combustion? how would carbon be formed before the cylinders i know they get clogged up but i didn't think it was carbon didn't know what it was lol

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I'm guessing DEs have an oxygen sensor similar to DETs and it may have failed. A failed oxygen sensor will clog up your IACV with carbon deposits and cause the problem you have described.

how does a bad 02 sensor clog up the iacv wouldn't it just cause it to run lean or rich

 

Yes the car will run richer, and with the richer mixture you get the carbon buildup. As I understand it the O2 sensor only comes into play after the car's reached operating temp where it adjusts the idle characteristics of the engine to suit. If it's not working the ECU doesn't get this signal. A stuffed sensor won't bring up a fault code either, only if the circuit (wiring) is physically broken.

 

It'd be something I'd be looking at anyway by what you've described.

 

I don't get any of this, how will the air going into the throttle body become richer as what chris has noted, aswell as the o2 not adjusting idle at operating temp... But actually going closed loop and adjusting mixtures at cruise speed instead.

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the aic robs air from the throttle body so less goes in the manifold less air means richer

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Had a very similar problem in my car, only it wouldn't even hold an idle. After a thorough cleaning of the ISCV it made it better for a day or so then back to it. Replaced the unit with a different one and it hasn't happened since. The one I removed was completely spotless so you wouldn't even know it was faulty looking at it.

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Thanks for everyones input, I'll work on removing the entire unit today (finally its the weekend). Hopefully just a lot of cleaning will fix it. thanks again!

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I'm guessing DEs have an oxygen sensor similar to DETs and it may have failed. A failed oxygen sensor will clog up your IACV with carbon deposits and cause the problem you have described.

how does a bad 02 sensor clog up the iacv wouldn't it just cause it to run lean or rich

 

Yes the car will run richer, and with the richer mixture you get the carbon buildup. As I understand it the O2 sensor only comes into play after the car's reached operating temp where it adjusts the idle characteristics of the engine to suit. If it's not working the ECU doesn't get this signal. A stuffed sensor won't bring up a fault code either, only if the circuit (wiring) is physically broken.

 

It'd be something I'd be looking at anyway by what you've described.

 

I don't get any of this, how will the air going into the throttle body become richer as what chris has noted, aswell as the o2 not adjusting idle at operating temp... But actually going closed loop and adjusting mixtures at cruise speed instead.

the aic robs air from the throttle body so less goes in the manifold less air means richer

 

Yer in the comoression chambers... Not the inlet manifold... Further confirming what yourself and i are on about with not clogging the iac.

That said the ecu adjusts/compensates the fuel when air is restricted anyway.!!!

 

 

 

OP, was the car auto at any stage and now manual.??

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yeah the only way how i can see how any combustion gases particles would get to the aic is through the egr but i don't think that would re circulate too many particles to block it up, i don't understand all the systems well enough

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i thought it just got gunked up over time due to tiny stuff that got through the filter and maybe small particles from crankcase blow by

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check the TPS setting... the voltage should be 0.5v so the idle stabilisation comes in.. it can be in some cases the fast idle cam is stuck.. or the throttle body is dirty and doesnt return properly.. it only has to be a tiny amount and it wont work well.. you will also see your fuel consumption go crazy.. as normally on decel you will get a fuel cut if it sees the throttle closed..

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I swapped the iacv. Now instead of idling perfect one start up an warm up temp it idles close to 2k the whole time sometimes dropping down to

1.1ish?

 

Rb20det

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Wait . Now I'm confused. Is it the iacv or the tps connected to the throttle body? I googled both and American websites are saying its both :/

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IACV ia valve commonly found on the inlet manifold that bypasses air around the throttle body... TPs is a sensor connected to the throttle body shaft that measures how open the throttle is and gives a voltage..

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Okay so this weekend I was able to remove the IACV and clean it out thoroughly using a carb cleaner and for a while it was fine. I gave it some more "spirited driving" and it started happening again, this time, when I start up my car I had to rev it to prevent it from dying (something that didnt happen before)

 

But luckily my friend came over and (you'll have to forgive my lack of specificity) but he showed me that to the left of my plenum were two plugs, he unplugged the top one, unscrewed the black valve, cleaned it out, and held his finger over the hole while i started my car and told me to keep revving. After that we turned the car off, and he screwed the plug back in a little bit, told me to rev some more, and only after we more revving and turning the screw looser or tighter did we plug the top back in. and my idle issues haven't happened since...

 

I'll try to take pictures of what "plugs" i'm talking about, again sorry for the lack of technical terms. Thanks again for everyones help. and hope this forum will help others

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If you can post some pics of the plugs man that would be awesome :)

 

Glad to hear you got it sorted out - hopefully i can resolve my high revving on idle with this info too :)

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Yeah post pics

 

I replaced the iacv and the other one and now my idle is worse. Idle is at like 2k

 

As apprised to the first time it idles fine until hot

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If you changed iacv and it Idles high, you probably just need to get the car up to running temp and adjust the idle screw to lower your idle to what it should be.

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So replaced both this iac and acc? I think. One on the back on the intake and one on the throttle

 

Got the car to working temp and adjusted the revs by the screw on the back on the intake manifold.

Got the revs down to 1k just under and it won't hold.

Drops and dies yet works fine at 1.5k-2k revs?

 

Ideas. ?

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