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Discussion Starter #1 (Edited)
As the title suggests, I’m having an idle issue that isn’t exactly typical. I have a 1996 integra ls with a stock motor. It has a new distributor and alternator. The car first had a slight occasional surge from 1k-1.2k. It was throwing codes for the IAC, crank position sensor, and evap purge flow. I had the car serviced and had rear main seal, timing belt, water pump, oil pan gasket, and clutch all replaced. After I got it back I replaced both the IAC and evap purge solenoid. The car began surging up and down between 1k-2k non stop unless I’m driving and will continue if I take it out of gear. Also aggressively bucks the car back and forth if I drive at really low speeds. Now the car is only throwing codes for crank position sensor, and another one for P1508. I know that code can be for wiring but also about anything involving the intake. I just need some opinions on some strong possibilities and I can’t find anything specific to this scenario in the forums. Any input will help.
Thank you
 

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Does it start doing it after the car warms up? If so, you have a faulty IACV or the wiring. You mentioned that the IACV had already been replaced. I've been on the same boat where the IACV that I purchased used was also bad, and the problem persisted until I installed a brand new IACV. Also, I had a similar issue about 20 years ago with my 96 GSR. Actual ECU was the culprit at that time.
 

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Discussion Starter #3
Does it start doing it after the car warms up? If so, you have a faulty IACV or the wiring. You mentioned that the IACV had already been replaced. I've been on the same boat where the IACV that I purchased used was also bad, and the problem persisted until I installed a brand new IACV. Also, I had a similar issue about 20 years ago with my 96 GSR. Actual ECU was the culprit at that time.
It’s a brand new IACV. Straight out of the box. The surging, however, happens no matter what. Start the engine and it will idle high for maybe 10-30 seconds and then start surging. Drive normal and it’s fine. Take it out of gear and it will keep surging. When I unplug the IACV while it’s warmer then it will just die. I went ahead got a new throttle position sensor and installed it today and cleaned the whole throttle body as well as getting a new gasket (found out old gasket is absolutely f****d lol). I haven’t bolted it up yet but I’m hoping it will help. I keep getting told there might be a bad leak. Next is either the intake or exhaust manifold gasket because one of those might be bad as well, probably both
 

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Also following, our 94 LS is doing the same thing as OP, and we have changed all of the relevant parts, too.
 

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Discussion Starter #6
So quick update everyone. First, I’ve heard of certain electrical parts having to be “calibrated”, so I was wandering what the chances are that my new IACV is bad. I put the old one back on and although the idle is still funky, all I had to do was tighten the idle control screw on the throttle body (lowering the idle) and it helped stabalize the idle and doing that didn’t help with the new part. It’s still unpredictable but for the most part it is less likely to surge so intensely when it does. I can’t be sure if my new IACV is bad (it might just not be up to oem specs) but I’m convinced there is something else wrong because the engine will do weird things with the idle with the new part and the old one when. I also have weird smoke or steam coming from behind the intake. Seems like it’s coming from one of the coolant hoses connecting to the IACV. Also smoke comes from what seems to be the exhaust headers when I rev while warm. Im gonna change the intake manifold and exhaust manifold gaskets to try to plug up any air leaks. Also gonna see if I can get an oem Honda IACV instead of aftermarket. If you have anymore suggestions then have at it please
 

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Discussion Starter #7
I actually just found something else out completely by chance. It sounds ridiculous but it’s worth investigating and I’m not too sure but it could have something to do with my current problem. I just found that when I am at a stop in my car is idling, it idles higher the more I pump my brakes and then will fluctuate and go back to a normal idle when I stop. I can repeat this over and over. Just food for thought. Any ideas?
 

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bad vacuum lines somewhere? Brake booster runs off engine vacuum. if the idle is rising when you pump the brakes there could be a bad vacuum line or plugged valve somewhere.
 

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Discussion Starter #9
bad vacuum lines somewhere? Brake booster runs off engine vacuum. if the idle is rising when you pump the brakes there could be a bad vacuum line or plugged valve somewhere.
I kinda didn’t know that haha someone actually told me when I got the car that I would need a new break booster as well. Would that be worth a try? I’ll probably swap it out eventually anyways
 

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probably wouldn't hurt if you know the brake booster is already bad/going. you can also do a vacuum leak test by either the cigar test or the soap water test. Cigar test is using smoke to find positive or negative air leaks, soap test typically works on positive air leaks.
 

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I had a 98 LSV that did the same thing. I was driving to work one morning and then all of a sudden the RPM's started hopping from about 800 RPM's to about 1800 RPM's in traffic. Took it to the local mechanic. They couldn't find a vac leak or any real main issue that could cause it. So all he said he did was took apart the intake, cleaned out the intake pipe, cleaned out the throttle body really good and changed the intake filter. Fixed the issue. He mentioned adjusting the idle some, but never needed to do that. Not sure if this resolves your issue, but may be worth taking a shot.

Good luck!

- DM
 

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Update on ours, too... After driving distances at freeway speeds (like an hour or more), the idle surge stops, and the engine runs smoothly. After you turn it off and it rests, it comes back though. :/
 

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So Update on my surging issue. I removed and blocked off the IACV on my manifold/tb and mine didn't go away but it surges less... not sure what to make of that. again my engine is coated with sludge and needs at minimum a headgasket so I'm hesitant to recommend anything what so ever :D
 

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Discussion Starter #14
Everyone seems to be having great luck with this lol a quick update to the thread though: I’ve been playing around with the idle screw on the throttle body and the idle valves that I have (switching them back and forth) and I changed the whole intake to a new cold air one. I checked my plugs a little bit ago and all except one look good. Well now for some reason the motor went from dying if it idles too long, to dying once it’s warm. It’s fine on start up but as I drive the car and it warms up, once I come to a stop it will begin to slowly drop down the rev range and come to a halt unless I give it gas or hit the brake pedal (I said previously the engine revs a small amount when I play with the brake pedal).
Im taking the car in for a full engine rebuild to prep for boost especially with a possible spun bearing. If anyone has any info on the sudden warm engine death then let me know. Otherwise I’ll keep the thread updated afterwards
 
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