Unfortunately these are common older car problems. Any vacuum leaks can cause idle fluctuations. Those can be from seals, gaskets and components attached to the engine's intake track. ​A smoke test could help identify leaks as opposed to shotgunning parts.

The reason activating the ac may seem to calm down the symptom is due to idle rpm being raised when the ac clutch engages. This higher idle speed makes surging less noticeable. Similarly putting the car in park or neutral reduces the load on the engine, making the idle rpm go up.

Manipulating the idle adjustment screw slightly more open or closed while observing the idle rpm may also be worth a try and costs nothing.

 

I forgot to ask, are you still getting a P0505 DTC? Or is it a generalized idle problem without code now?

 

No code, because I normally either shut car off so that it doesn't continue to rev, or I go in and out of park/reverse to make it stop. That's the other thing - when it acts up, I turn off car. I immediately restart car and revving doesn't return.

I realize I am very ignorant here, but if it's vacuum related (hose or seal or gasket or other), why would it be intermittent. It's not like I fix the vacuum leak......if it's a leak why would it not occur ALL the time?

 

As far as leaks: the car is 22 years old. The undercarriage looks like an oil spill factory. Lol. Though oils runs down onto the pans, it never shows up on garage floor. The levels on the engine and trans dip sticks are always where they should be. I can get 3k miles without being down on the dip stick. Car does have a valve cover gasket leak. In fact when car starts and warms up, I will get some light white smoke from the gasket area (gasket closest to firewall). I usually just clean the area every once in a while. I may get valve cover job and plugs next year but like I said, the leak isn't bad enough to where I'm losing oil.

 

The vacuum leak area can be sealed when cold and when the engine heats up it opens or vice a versa as pieces expand at different rates. By changing the load on the engine the affect of a vacuum leak can be much less noticeable but it doesn't mean it is gone. If you replaced the valve cover gaskets the upper intake manifold would have had to been pulled. This can be an area easily subject to vacuum issues. The upper intake gaskets should have been changed; that would include #11, #5 and #8 (although this one wouldn't cause a vacuum leak). The throttle body gasket, second picture #5 should have also been replaced. If any of these were reused it increases the odds of a vacuum leak. When gaskets are reused you always need to be prepared to do the whole job over. Sometimes it works, sometimes it doesn't. Sometimes gaskets get crimped when installing even new ones.

 

Thanks, Jon. Very interesting!
And please note - - - - this issue all started when I moved to Las Vegas, NV and had a buddy recommend a mechanic. This "mechanic" was hired to replace 1 valve cover gasket. I asked him to replace the valve cover gasket closest to the radiator (not sure if that is front or back or left or right). The gasket that is easily viewable. First, the mechanic had a hard time getting something off so then he said he had to take more parts off than he thought. And while he was working on it, I swear he dropped something either down into the intake (like an asshole) or somewhere else. He took a while trying to find it and ended up getting a magnet to get out whatever he dropped. Anyway....he put everything back together and as soon as I started the car, it started to rev up and down, up and down, up and down. This NEVER happened before. So bottom line, this jackass did something!!

So I ended up taking the car to Acura (twice) and they said he pinched the upper plenum gasket so they replaced it. They said they pulled the plenum plate and looked for other vacuum leaks but couldnt find any. I drove home....it started immediately when I put the car in park. Drove back to Acura and they looked it over again. They said they cannot (again) find any vacuum leaks or anything wrong, and they have no idea why the car revs up and down and said I should try a new ECU.

Maybe at this point, I just purchase new valve cover gaskets, the plenum gaskets, and whatever gaskets I need (found gasket set on rock auto), new plugs, maybe new coils, and have a real mechanic start from scratch and have him search for this or that while doing the job. Maybe there is an intake restriction he'll see? Maybe the intake manifold needs to be replaced too? We have to remember that all of this started when jackass mechanic "tried" to replace a valve cover gasket, which should not have been a big deal/huge job.

 

Also, if I want to go through with the valve cover gasket replacement job, I have a few questions"
1. Would I also change the coils?
The current coils are aftermarket but I guess they are fine - I never get engine light/codes. I just always assumed that Denso or NGK coils would be better?

2. Would I also change the intake manifold gasket?
Is it recommended to replace the intake manifold gasket during valve cover gasket job? The intake is pretty much exposed/up or am I incorrect?

3. In the image I am attaching, are these the full set of upper plenum gaskets? Also in the photo, is this set including valve cover gaskets? I was going to purchase the Felpro valve cover gasket set, which includes grommets and tube seals.

 

Also, last evening I drove car to casino (20 minute drive). Arrived at casino, put car in park, no idle revving.
Drove home, put car in park, idle revving (up and down).
I opened the hood and I started to try "moving things" or "pinching hoses".....
At one point I move the cluster of electrical connectors that run off of the throttle body.....when I did this.....the idle went high and stayed there for about 20 seconds. I moved the connectors again and it went back to revving. But at some point, based on me moving the electrical connectors that run off the throttle body, the idle stuck high.
Maybe I should "mess with" one electrical connector at a time and see if this changes the revving (next time it happens). Like......move the electrical connector from the IAC......then the others.......

Thanks!

 

The only other "problem" that my car seems to be having right now, is I am getting whining from the alternator, I think it is whining from the pulley on the alternator. Though I am not noticing any electrical issues, the whining is getting worse. It whines as the car accelerates and whines as its decelerating. I should probably get the pullet replaced or just do the entire alternator job.

 

1. I wouldn't change coils unless I suspected a problem with the coil.
2. I would change all the gaskets.(use the one throttle body gasket that fits, there are 2 use the correct one that matches. They include 2 since there are 2 configurations).



3. This set does NOT include valve cover gaskets. You will need to buy those separately. As mentioned before you will need to remove the whole upper intake assembly to get to a couple of the valve cover bolts, The air chambers cover them on both the front and the back. Replace the gaskets at the same time.

Concerning the other two posts you made:
I would try to recreate the idle changes made by touching the electrical connectors. I would also disconnect them and use electrical connection cleaner to clean both halves of the connector(s). I would do this before touching the upper manifold. I would also check the IAC gasket by spraying cleaner around the area when the idle is varying and see if it stops. If it does then the IAC valve needs a new gasket.
The alternator pulley is a pain to replace. This is due to the limited amount of space that is available to work. Look at the space and see if you have the tools and the confidence to do the job. Nothing worse then getting half way and discovering you not comfortable and don't have the tools to complete the job.

 

Thank you again, Jon!

In my Rock Auto shopping cart, I now have: 6 NGK Iridium Spark Plugs, 1 Upper Intake Plenum gasket set (picture provided), and also FelPro valve cover gaskets with grommets and seals. My question now is: Would FelPro valve cover gaskets be OK? Acura told me once to NEVER use after market valve cover gaskets. The price is significantly different.

I will try the steps you mentioned. The IACV is brand new (the throttle body is junk yard) - so I think the gasket should be OK. I was really careful when putting the gasket in. Will keep you posted.

 

Jon - on the diagram you posted, where are the F&R Intake Chamber Gaskets? In the diagram, I see valve covers, valve cover gaskets, upper intake plenum gasket, and intake manifold gasket. I am thinking the "mechanic" may have pinched the intake chamber gaskets...

 

Also, when the "mechanic" performed the valve cover gasket job, he literally pulled up the entire intake. I recall this because I was able to see the engine.....like the valve and that area. I didnt think that doing a valve cover gasket job would make you have to pull the intake up. So this makes me wonder......did he pinch or screw up the intake manifold gasket??? (worst mechanic ever)

 

The front and rear intake chambers are part #'s 3 & 4, the gaskets are #'s 5 & 6. Unless you are loosen the bolts on these you probably don't need to replace them unless you see damage, or hear air leaking, or want to take them apart to clean them. You do need to take the entire upper intake manifold off to get to the top bolts for the valve cover. Fel-Pro is a a quality gasket. The OEM's I think are better, at least for me they lasted longer than others. Just don't get a no name from Amazon or eBay.
If you replace the intake gaskets you can see if any are damaged but at that point you are replacing them so it won't really matter. Just make sure you have a nice clean area for the gaskets.

 

I purchased and used the electrical cleaner on every electrical connector that I could. No luck.

 

It was a long shot at best, the connectors on the cars are pretty good. Don't over torque the valve cover bolts (or any others for that matter). Luck.

 

Jon, Meant to ask you and considering that weeks ago when I put on a new IACV and junk yard throttle body (I cleaned it up beautifully), the car ran perfect, for several weeks (which it hasnt done since the problem started). I mean, it ran so well that it was noticeable. Even when I put the car in park, it seemed like the idle held perfectly. Whereas normally, before it acts up, it almost revs up a little bit before starting its problem (up and down rev). Question is: Any chance the problem is the ECU? My understanding is that the ECU does play a role in setting idle (along with other components). Acura dealership told me that they cannot find any issues after their diagnosis, so they said to try replacing the ECU. But if the ECU was faulty, wouldn't there be other problems?

Thanks!

 

A video is going to be really helpful here...In the manual for P0505 they describe taking the VSA enclosure off, then using your two fingers to cover the port where the IACV allows air from in front of the throttle.

Have your tried this and described your findings? if it's still fluctuating or is idling very high, there is a vaccum leak somewhere else. covering this port is supposed to make the idle go very low.

 

Domenic,
There is always a chance for the ECU to be damaged. Taking a connector off while the car is running could damage a transistor on the input or output of a signal line due to a spike in voltage. Always turn off the car and best to disconnect the battery before removing electrical connectors. You can damage one input to the ECU and not the others. I would check everything very carefully before replacing any ECU due to cost, time and a lower likelihood of the ECU being the problem.

The ECU basically checks inputs such as MAP sensor, IACV, throttle position, O2 sensor (when in closed loop mode, which should be most of the time), the fuel trim, timing, engine load. Many of these can be influenced by a vacuum leak. If you are getting the P0505 Error code POST THIS and all the readings from the items listed under live or captured data.

Do the testing as suggested by Whitetiger5. I put the page he is referring to below. I, like Whitetiger5 have seen the rear engine mount develop a leak (Usually around the top) causing a vacuum leak at idle. The front and rear engine mounts on these cars have a vacuum line input at the bottom to smooth out the idle even more than just a plain rubber mount. It works but it is noticeable when the vacuum can't be held by the mount. The line from the front mount is connected to the rear vacuum line using a 3 way hose adapter. This feeds into a solenoid near the firewall on the drivers side. Check every inch of the vacuum lines for cracking, nicks, or bad connections. You can take a vacuum pump and connect it to the line from the firewall and see if it holds a low vacuum for a few minutes, if it doesn't you can easily troubleshoot the leak.

Having a new to you throttle body work for a week or two then the original problem returning would probably make me look at something that would be a wear item such as the IACV itself.
You must start somewhere and have baseline to work from nobody here can tell you the exact problem and solution, we can only give you our best guesses based on our experience and knowledge. At this point you need to start taking things apart and seeing what you find. Clean all the items with the appropriate cleaner, check for the leaks using hands, eyes, and tools such as a vacuum gauge and OBDII reader. We hope to lead you to a solution but that is the best we can do without having the car in front of us. Let us know what you see and we will try to help you further.

 

I will try and post a video. I can show how it revs up and down when I put car in park. And how I stops when I then go into reverse and back into drive. Also, restarting the car also makes the problem stop. I usually turn off car or restart it so that the revving doesn't continue.

Also - the situation is always an idle that revs up and down. Not a fast idle. Just an idle that revs up to about 2.5k rims then back down......up and down.

Also, the junkyard throttle body.......I replaced the IACV with a brand new IACV......part isn't yet a month old.....so I don't think it's the IACV.

 

It is a Vacuum leak. You need to find it. All the things you said above are related to a vacuum leak Putting a load on the car by taking it out of park will smoother the signs of a leak, Turning it on and off will set the fuel trim etc etc to store ECU values. I imagine that when you turn the car on and off ,that without touching the gas pedal, that the RPM's are slightly different each time (as it depends on the LTFT stored when you turned the car off) . Once the car is started if you pressed the gas pedal the reving up and down starts again. Vacuum leak anywhere from the lower intake manifold to the throttle body, PCV, engine mounts, vacuum solenoid.

 

Jon - you are right. When I restart car, it will be fine. But then if I hit the gas pedal, it will start again. Basically, anytime it is fine, if I rev engine/hit gas pedal, the problem reoccurs.
Ok, so definitely vacuum leak. Sucks that Acura charged me a shit ton of money to replace the upper plenum gaskets (which they said were pinched), but the problem still occurred. Acura pushed me away and said it was ECU.
But we have to remember....this all started when a mobile mechanic changed the valve cover gasket. As soon as he put the car back together......BOOM....the problem started. He did something. He wasnt the sharpest tool in the shed!
So to me, I will keep searching for the vacuum leak and maybe do the smoke test and take professional help with finding the leak. And, since the valve covers need to be replaced anyway, maybe by doing that job, the proper mechanic will be able to fix the mobile mechanic's crappy work (or whatever he did). I can tell the proper mechanic about the situation and he can look for this while he changes the valve cover gaskets.

Questions:

if the vacuum leak is within the intake manifold as I suspect, how would I find that? I would need to take to a mechanic, correct?

What is a vacuum solenoid and where is it located?

I really wish I knew what the hell this mobile mechanic did! Other than this issue, the car runs perfect!!

 

Will take another video when car gets to temperature. But with current video.....no issues.

 

With issue....

 

 

Also, what is best procedure for "spraying" to look for vacuum leak? Water bottle mist? Do I need to spray areas with intake/carb cleaner? Brake cleaner? Is there something special to use?

Thank you.

 

You're sure the breather cable is securely plugged in?

 

Domenic, The video is what I would expect for a vacuum leak. I did notice what looks like a bolt missing from the top intake cover. It could just be the camera angle though. If a bolt is missing you can have a leak right there.
You can use carb cleaner, water, etc on the outsides. The bottom of the intake manifold is basically unreachable. Replacing the gasket is the easiest way.
The vacuum solenoid I mentioned it the control solenoid for applying the vacuum to the motor mounts. you can follow the vacuum line from the motor mounts and it will connect to the solenoid, Driver's side, near firewall around/under were the sway bar bends.

 

That plate/gasket will definitely expand/contract at a different rate that the surrounding area and be inconsistent (in terms of sealing) as the engine gets hot. i.e. vacuum leak! Nice eye Jon.

 

Will check breather cable. I think in the past I thought it was "not in all the way" (in to the tube).

 

Nice catch! Recently, when I took the plenum plate up to clean the area and EGR port, I tightened that bolt too hard and it snapped. It is snapped off, inside.
Just weird that it was fine for over 2 weeks, and now is pretty much every day.

 

I have no idea how to get the bolt out.....was going to have the mechanic handle the snapped bolt issue when I had the valve cover gaskets (and ALL upper plenum gaskets) replaced..........

 

I will post a video of spraying water (mist) around several areas to see if anything changes.
What would be the best time to try this?
When (if) car is experiencing the revving problem?
When car is hot? When car first starts?

I have sprayed around the snapped bolt area in the past and the revving never changed. The only change I ever experienced was when I moved some wires/hoses around, and the revving stuck as a high idle, and then went back to revving again.

Thank you!

 

UPDATE: The breather tube was clearly not inserted in its entirety. I just inserted "all the way"........

 

You would spray when the car is revving up and down and monitor it for a short change. I would fix or get fixed the snapped bolt. Did the breather tube being inserted make a difference?

 

After inserting breather tube, I started car and also revved it a few times. No issues. Though generally.....problem seems to happen when car is hot.

I still can't get my arms around something: if it's a pinched gasket.........if it's a vacuum leak........if it's the bolt on the plenum plate.............why would the problem be gone for almost three weeks after I replaced throttle body and new IACV? maybe because when I did the job I had the battery disconnected for a few days?

 

When the car warms up the metals expand without the gasket being good a gap would occur and then the vacuum leaks. As far as the "new" throttle body, I can guess a few things, the system was ECU was reset when you disconnected the battery, the computer then was able to compensate for the new pieces. After being on for a while the maybe something recently bolted or reconnected (tubing) loosened just enough that the ECU can't compensate. Maybe when removing and replacing the throttle body you jarred something and moved just enough to close the vacuum leak but after running the car for a while the vibration has moved it back. I don't know the condition of your car etc so these are just possible guesses they may not be probable. I would have been replacing all the gaskets and the vacuum tubing to be done with it. Did you do the vacuum test with the throttle body we recommended?

 

I have not performed the vacuum test on the throttle body yet......though when Acura performed their diagnosis, they said it proved the IACV was good. That is when they started to search for vacuum leak. But of course, several hundred dollars later, they then blamed it on the ECU.

Just updated my Rock Auto shopping cart to include NGK Iridium plugs, FelPro Valve Cover Gaskets w/ grommets and seals, and full upper intake gaskets......going to schedule the job for next week with reputable mechanic, and will also give him a full explanation of what has been covered in this thread.

 

Drove car about 20 miles, mostly highway, car ran great. Put car in park, no revving. Perfect.
Left casino, drove another 20 miles, went to get takeout, put car in park, rev up and down and up and down. Then went to another takeout place, put car in park, no revving.
I guess I just dont understand how things work and/or I am stupid/ignorant. But the car is HOT. It was hot when I put it in park and then it was hot when I put it in park again. How gaskets and air leaks can change the way they do due to changing the load on the engine, literally seconds apart is weird to me. I literally put car in park....it revved up and down. I then put car in reverse then back in park and it stopped. Must be alot going on. One minute it revs up and down and minutes later it will not.
Purchasing valve cover gasket job parts today, which includes intake manifold gasket. Just not sure what else I need to purchase for intake manifold gasket job, since I never performed one or bought parts for one.

 

It seems there are some air pockets in the coolant system. Make sure to burp them out.