I have 2000 Acura TL V6. The symptoms are that when engine is warm and I put in Park, the idle goes up and down. Or when I approach a stop light, and almost come to a stop, the idle very briefly goes up maybe a only one hundred rpm's and then goes back to normal. I had this issue maybe four years ago and replaced the IACV, and then problem went away. So when this happened again now, I was very positive that a new IACV would solve it again. So I bought another $20 IACV on Ebay and installed it, but still had the same problem. So now I am thinking about replacing the Throttle Position Sensor. I am just wondering if the TPS could really cause the symptoms I am having, and it is just a dumb idea to even try it since maybe I will make things worse by doing the TPS removal (by dremeling the mounting screws with no heads), installing new one, and calibrating.

In doing a lot of reading, obviously everyone points to the IACV, but some mention a handful of other things like vacuum leak, bad coil, bad spark plugs, etc. But I am thinking that none of these other things would be likely given the symptoms I have, and I would have other symptoms if it was something else. I guess I could have gotten a bad IACV too and could try another.

In any case, just wondering if anyone knows if a bad TPS could cause these exact symptoms just like a bad IACV would. Thanks!

 

I am leaning toward vacuum leak. engine has some additional air coming in and has to adjust (via the IACV) to bring the RPMS back to the correct range. Did you remove the throttle body when replacing the IACV? I think there is a paper gasket between that and the intake manifold? should be replaced. additionally, a worn engine mount could be giving you a strange idle as the car draws vacuum to control the rigidity of the engine mounts. if they are broken then air could be escaping that way.

 

As whitetiger5 mentions, check all the connections & vacuum hoses shown in the link below:
Engine Mount for 2000 Acura TL | Delray Acura Parts (acuraoemparts.com)
I had a similar problem and found the #29 & 30 hoses disconnected at #11.
Good Luck!

 

Ok, thanks for the quick replies, and looks like I should lean towards vacuum leak at this moment rather than TPS. I will start checking hoses per zeta's diagram and check motor mount per whitetiger5, that is if I can get some great lighting in the dark evening tonight/tomorrow night (generally I always like working in daylight in engine compartment since not so many shadows as using artificial light!).

Question....I was not aware of how vacuum is used in a motor mount. I see the vacuum just goes to front motor mount per the diagram. Let's say front motor mount itself has a leak. Can I just remove the vacuum hose from the motor mount and plug it with something like screw or pin/clamp, and see if problem goes away?

By the way, I did not replace the TB gasket when I removed it as I was not originally planning on removing the TB to replace the IACV, but I ended up removing it since I needed to use a vice grips to remove the screws on the IACV. I was thinking the gasket joint seemed so tight with old gasket that there is no way any amount of air could get thru, but maybe that is a wrong thought and I need to replace the TB gasket per whitetiger5's post.

 

Correction on previous post, I see vacuum goes to two of the mounts so I need to check both. So is it ok if I just plug hose #29 and see if problem goes away?

 

I've put my throttle body back together without a new gasket more than one; and sometimes it leaks. The instances where I've replaced the gasket; it's never leaked.

 

there's not a lot connected to the manifold. you can isolate by plugging/capping hoses one at a time. make sure the evap hose and fpr hoses are connected and not torn. had large leak once at the throttle body where i had removed the evap hose and forgot to reconnect. car ran fine for about 20 min and started surging. if you still have a rolling idle suspect the throttle body or plenum gaskets.

 

Well on the way home late tonight from work I made one errand stop and then to home, and the idle up and down after putting in Park did NOT occur. I was so surprised. So I then really can't troubleshoot until the symptom is again repeatable.

I did inspect the rubber hoses and metal vacuum lines going from solenoid to rear and front motor mount. The rubber hose pieces of the lines look really good and are soft, but the metal part of the line going to the front is heavily rusted since it is on bottom side of car. See first pic attached which is the underneath line going to front mount. The second pic is metal part of the line in engine bay going to rear mount, and that looks good. So metal part of the front line could be bad or one of the motor mounts could be bad.

So when the problem starts again, I think I will just pinch the rubber hose just coming out of the solenoid, and see if the idling up and down just stops.

I think next step would just to replace the TB gasket per above posts since that is easy to do. I will update on Saturday since that would be the first chance I have to replace the TB gasket.

Again, I will have to wait til problem happens again, and then do the two steps above

 

^
Just curious, even though that front metal vacuum line looks 'crispy', did you perform the 'idle relearn' procedure after replacing the throttle body / IAC valve?

Refer to the attachment below:

 

Oh, I did not know there was a relearn for the idle! I have heard of a reset/relearn for newer cars, but not for such an older car. If my Acura exhibits the idling problem today driving to or from work, I will give the relearn a try tonight!

 

Update....On way to work this morning and shutting off the warmed car in work parking lot, I did NOT get the fast idle up and down when putting in Park. Went home in evening and parked at home and I DID get the fast idle up and down in Park. While the idle was going up and down, with a pliers I squeezed the rubber vacuum tube that comes out of the vacuum solenoid and that goes to both engine mounts....nothing changed and the idle just kept going up and down. But I did hear the solenoid clicking each cycle of the up and down of the idle....not sure if this is expected/normal as idle goes up and down, or if the solenoid is bad.

In any case, I could not perform the idle relearn right away per zeta's post above since the idle was going up and down. A couple hours later I performed the relearn and waited it to get up to temp per the instructions. HOWEVER, during the 5+ minute idle relearn process, the check engine light came on and it was a P0505 code, which points to a bad IACV or vacuum leak.

I will see what happens in the next couple of days after the relearn, but I am doubting it fixed the problem due to the P0505 code per above. Now I am thinking one scenario is a bad new "cheap $20" IACV, and I am thinking of putting the old 4-year old IACV back on (after taking it apart and cleaning it) along with a new TB gasket. I would do this on Saturday if I get the bad idle up and down in Park. Then if that doesn't work, scenario B would be finding a vacuum leak. I am doubting it is a vacuum leak with engine mounts/tubes since the squeezing the tube with a pliers per above did not help. Or I guess could be a bad vacuum solenoid per my first paragraph above.

Still wondering why it only happens while in Park....just wondering what the engine/computer are doing and thinking such that the only time I have the problem is really in Park.

 

^
In order to perform the idle learn properly you must either disconnect /reconnect the battery or pull the No. 13 Clock backup (15A) fuse from the passenger side under dash fuse box for a few minutes and reinsert. This resets the ECU. Then turn off all electrical draws (Radio; AC; lights et al). Start the car without touching the accelerator pedal and just let it idle for two to three fan cycles.

 

Tried the relearn again per above post by pulling out the clock fuse for a few minutes and then letting the car idle. But after maybe 3 minutes, the idle started going up and down again, so could not complete the relearn. So maybe back to plan of redoing the IACV and TB gasket.

 

I’m fairly certain there is a vacuum leak and the IACV is trying to control that. Did you attempt the troubleshooting on page 11-148 that descibes disconnecting everything in front of the throttle plate and covering the IACV port with your finger? If you have high or fluctuating idle after this it should point to a vacuum leak.

I think that it only obvious in park or neutral because the engine isn’t under load due to the torque converter being engaged.

 

+1 on vacuum leak. check ALL your rubber hoses, one of them is leaking

 

Ok, I will take a look at 11-148 troubleshooting procedure and inspect all hoses. I think I will do this on Friday when I can take a 1/2 day off and have good daylight to help inspect hoses.

@thoiboi, I can start looking at parts diagrams to maybe help me identify "all" vacuum hoses. Or is there a simple way of identifying or following "all" the vacuum hoses?

@whitetiger5, thanks for hint to 11-148. So just to help clarify my understanding....If I cover the port with my finger and the idle still goes up and down, that means air is not going thru the IACV and instead air is getting pulled in thru a leak somewhere else? If I cover the port with my finger and the idle stops from going up, I know the IACV was actuating and letting air go thru, and so maybe IACV is bad? Is that a correct understanding?

Thanks for help and time!

 

If you disconnect the IACV and surging stops then you know it's there. If the surging (or increased RPM) continues further after you have blocked the passage with your finger, then you know that air is getting in elsewhere.

 

@whitetiger......ok, if I get home today in my driveway and the surging up and down is happening when I put it in Park, I am thinking I leave the car running (with the surging up and down happening), and just disconnect the electrical connector to the IACV. If the up and down idling now just sticks to one speed, then I know it is the IACV that is causing the up and down. So I am thinking I can do the test just by unplugging the electrical connector to the IACV while the surging up and down is happening, right?

 

Not entirely, you have to unplug the connector and cover the port. If I understand the manual correctly, you're trying to eliminate the number of places air can get in. So far: the throttle valve, IAC valve and then whatever leaks there may be; if you just disconnect the valve that doesn't mean you disconnected it in an open or closed state (which is a variable). you must cover the port with your finger you know for certain it is closed.

If after this the idle speed does not drop then the manual states to check that the throttle plate is completely closed and inspect for leaks.

 

I got home very late last night, and the idle was going up and down when I put it in Park. Since it was dark and cold (nice crisp Wisconsin fall weather), just for kicks I just opened the hood, with engine idle still going up and down, and quickly disconnected the electrical connector to the IACV. The idle then just stayed at a higher level, and really did not move around....probably IACV was in an open or partially open state when I removed the connector. So I am thinking it is just the brand new IACV not operating correctly, and first thing I should just try is replacing the IACV (and TB gasket as whitetiger5 originally recommended) and see what happens. Also I will inspect as many vacuum hoses as I can identify and see. I took the old removed IACV (only 4 years old) and cleaned it. I removed the electrical/magnetic piece from the IACV metal body, and the rotating valve piece inside was pretty "sticky" and did not spin very freely, but not terribly gunked up like one might expect if it had been 15-20 years old. I cleaned it and now spins really nice, so I will give it a try and report out after I get a few more trips on the car.

 

I don't mean to sound like a broken record but, you really can't leave things to "probably." What if your new IACV is perfectly fine and it's just the throttle body gasket? or perhaps the seal between IACV and throttle body is not properly seated? Being thorough with diagnosis will be the best tool you throw at it.

 

Just to add some later notes in case someone comes across this thread. I had replaced the IACV with a cheap aftermarket one, and it did not fix the problem. I purchased another aftermarket IACV and the problem did not go away. I then incorrectly made the conclusion at that time that the IACV was not the problem since I tried two brand new ones. Then I tried other things to find the problem like smoke test, propane test, inspecting every vacuum hose, burping coolant system, electrical measurements, etc etc. I had no success so I just lived with the problem for 1.5 years. Then I came across another thread this past month, and this other thread eventually lead to one suggestion to try an OEM IACV. So I purchased a used OEM/Denso one, installed it, and the problem went away!!! So the conclusion is that you can try a cheap aftermarket IACV to fix the problem, but if that doesn't work, you probably need to try an OEM/Denso one at some point (after eliminating some other causes).

 

A very long class but a lesson for all of us.

Glad it's working properly now.

 

I have the same issue on my Acura TL 2003 Type S. We have gone through 3 IACVs each either after market or old from a junkyard. We did the exact troubleshooting steps in the service manual pages: 11-148. But we have no CEL. The idle surging in park stops when the bottom port within the throttle body is covered. We have a throttle body and IACV that is supposedly oem-refurbished, now. We tried check for vacuum leaks, could not find any, any suggestions on the best place to check for this would be helpful. NO CEL. And Surging stops when IACV port in bottom of TB is covered. What does this mean? Replace the IACV with OEM or Denso? Or is there a vacuum leak somewhere else in the system and the IACV is trying to compensate? The car idles fine for 1 minute while it is cold, then idle surging starts, 1-2k rpms. Thanks guys.

 

have you tried clamping the air assist tube? The behavior you’re describing sounds similar to something that I recently experienced where when the engine is cold, the surging doesn’t occur immediately, but as the engine is warming up, the surging will take place. Once the engine is completely warmed up the surging goes away.

 

That's a good idea, we will try that tomorrow. Will get back to you and let you know what happens. Appreciate the response man.

 

Okay so we ended up just going out and getting a brand new iacv, installed and now the surging has completely stopped while idling. The car feels weird in gear though while driving it sputters a little bit when letting off of the gas pedal. But now we have P1519, Nooo! Maybe this weird feeling in gear is a result of this code?

So we are going to follow the exact procedure in the service manual to troubleshoot P1519.

Do you guys suggest we follow that or is there a known solution at this point?

I’ll get back to this thread once we try the full set of troubleshooting steps to let everyone know what we find. Thanks.

 

Not sure if this was resolved but......from MUCH experience, the IACV must be replaced with genuine Honda OEM part. No substitutions. Gotta bite bullet and pay....if you can find in stock. Once in a while, aftermarket will do the truck. For me, after many aftermarket IACV, only the ORIGINAL worked (immediate resolution).

 

Did you ever find the solution to your problem? Going thru same issues with my cls6 for the 3rd time now. Mine isn't just the annoying idle surge, it actually bucks when in gear and when in neutral it idle surges. Did you ever find what was causing the p1519?