Hi and thanks for the forum to ask questions. I have a 2001 CL with 225k miles. I've had the car for a long time and it's been a great car. A few months ago it started surging at idle only when cold. The RPM dips to almost stalling then comes back up. It idles fine after fully warm. Idle Air Control Valve, right? Hmmm... I've replaced it three times, the last time with a new Honda part (16022-P8A-A03), yet the surge continues. No check engine light. I've also replaced the Throttle Position Sensor and set the voltage values correctly as well as replaced the MAP Sensor and cleaned the throttle body bore of carbon buildup. Last, I have thoroughly bled the cooling system (multiple times) to ensure there are no air pockets to give false temp sensor readings. Because there is no CEL, I'm lost where to look or what to replace/adjust. Any thoughts would be great appreciated! I did search the forums as well as Google and found many Honda idle surge issues but everything I've read suggests the IACV but that doesn't seem to be my problem?

 

^
Check all of the vacuum lines and their respective connection points thoroughly. You have a 22+ year old car chances are one may has disconnected
or dry rotted through? Use the diagrams below to trace them out for careful evaluation:

Especially check the two connections at the #12; Valve Assembly, Electronic Control Mounting Solenoid ; Hydraulic Control Unit below.
I had a similar 'dogged' surge that I could not get rid of in the past and after in depth under hood review, 'stumbled' upon one of the vacuum hoses on #12 had disconnected completely. Reattached it with a reinforcing small cable tie and the surge was cured.

Good Luck!

 

Excellent tips. Thanks @zeta! I'll report back here after I check...

 

I've been dealing with this same issue for awhile now. Seems to be completely random on start up. Sometimes it'll drop to the point of almost stalling, sometimes it won't. I took the line off for the front hydraulic mount that's connected to #12, with no change. But I'll look at it again with this information.

I'm starting to think my engine has a bad head gasket or warped surface though, because oil keeps leaking at the front of the block underneath the head. So that might be it, until it warms up & expands.

 

No luck on the vacuum lines, @zeta. Everything appears to be in place, connected, and secure. Back to the drawing board.

 

did you check the cam thrust cover? could be leaking there and running down around the front below the head.

 

coolant system is burped? you've checked the EGR passages?

 

Thanks @whitetiger5. Yes, cooling system has been bled a couple of times. EGR passages are remarkably clean!

 

Only other thing that I can think of is when you had the throttle body off the IM for TPS replacement was the TB gasket in good shape to reuse?
TB bolts were torqued to 16lbf-ft.?
When I look at the TPS on my CL-S6, I see a green factory installed gasket. A replacement gasket was provided with your new TPS kit?
It's strange that this surge remains with the installation of an OEM IACV.

 

@zeta Yes, there was a new gasket with the TPS and the gasket from the throttle body to IM was also replaced with new. I didn't use a Honda TPS so maybe I need to pony-up for the good stuff but I've been reluctant because everything points to IACV.

 

I haven't checked that, no. Didn't notice anything unusual when I did the RL cams. But there is definitely oil under the front cover. Easy to get to and check thankfully.

You replaced the TPS? Did you dial it in correctly?

 

@Thefireball Yes, I set it carefully. I don't recall the voltage spec, but it was set closed and then open.

 

Yeah, looking at everything everyone has suggested, and they check out as OK, it perhaps sounds like the particular TPS brand used may be the weakest link?
Especially in light of the money you paid for an OEM Idle Air Control Valve.
I don't believe Acura / Honda sells a TPS separately, they make you purchase the whole TB assembly.
The guy on the thread below used a Blox BXIM-10400 on his 2G TL & found joy if you decide to revisit the TPS.
throttle position sensor - AcuraZine - Acura Enthusiast Community
Here is the cheapest one with free delivery I could find.
Blox Racing Throttle Position Sensor TPS for Honda B/D/F/H Series | eBay
Good Luck.

 

@zeta , Is the TPS the same on the 2G as my car? It appears to be but I'm not expert enough on these things to know for sure. And you are correct, you have to purchase the entire TB from Honda to get the TPS.

 

and
??



You stated in your original post that you have '2001 CL'. (it is either a second generation CL Premium or CL-S model with the J32A1 or J32A2 engine, respectively):

The individuals second generation TL the Blox TPS was used on, in the thread I linked above, is a 2000 TL Premium because the TL-S model was not made until 2002.

However, the throttle bodies on the J32A1; 2G CL / TL Premiums are different than the J32A2; 01-03 2G CL-S & 02-03 TL-S models:
J32A1; CL Premium:

J32A2; CL-S:

The TPS', though, appear to be very close to being the same on both throttle bodies.
My best guess is that there are differences, though, I'm not exactly sure what they are.
It appears, size-wise they look close?

 

@zeta Yes, that's what I saw when I looked up the TB for the TL and my CL (not a Type S). TPS Appears the same but I'm guessing they are not. It's not a terribly expensive part. I could try one and see what happens. I wish there was a CEL/OBDII code, that would help so much.

 

^
I understand the reluctance to replace the current TPS especially without a code.
That's what drove me when mine was acting similar.
Even after I replaced the old factory IACV with STANDARD MOTOR PRODUCTS AC229, up & down, up & down.
BTW, what brand / part # identifies the current TPS that you have installed?

 

@zeta It was an eBay part. At $32, it's probably junk. If you have a recommendation for a particular brand, I'm all ears. https://www.ebay.com/itm/235110632421

 

A couple of things that may or may not be related/help diagnose:

• When the engine is surging, if I turn the engine off and immediately restart, the surging is gone.
• There is a 'flat spot' that happens the first time I push the accelerator on a cold engine. The engine does not respond. When I let off and push the accelerator again, the car accelerates. It only does this once.

 

@zeta This is fixed. Turned out to be, as you suggested, the junk aftermarket TPS I put on the car a while back. I set the voltage multiple times to no avail. I ended up buying a used throttle body on eBay which still had the factory TPS on it and voila!, problem solved.

Moral of the story: even the "good" aftermarket TPS' are junk. I hated to buy a new throttle body from Honda just to get a new TPS so I went the used route and it worked out fine. I paid about $75 for the used unit from a reputable seller.

Thank you very much for your input on everything. Greatly appreciated!

 

^
Good to hear.
I've heard the same about the OEM denso IACV versus the aftermarket ones.
Though I have used the Standard Motor Products AC229 twice now with no issues.
More Information for STANDARD MOTOR PRODUCTS AC229 (rockauto.com)

 

I've been struggling with an "iacv" idle problem when the engine is cold. any throttle input when cold or warming up causes the the idle to surge after letting off the pedal.

the problem goes away after restarting.

after reading @thebman 's post about behavior and resolution..the luckiest thing I may have done here is taking the entire throttle body when I went to the pick a part recently.

if the problems still there in the morning when its cold I'll be replacing the throttle body and keeping my fingers crossed.

it was strange because the OBD II scanner shows 9.8% throttle at idle and same voltage from the junkyard part (9.41% to be exact).

will find out in the morning and report back...

 

Turns out my problem, was a little bit different… After replacing the throttle body with that from a junkyard, I was still experiencing the same issues:

• Idle surging after letting off the throttle during the warm-up phase.
• High idle when cold
• restarting the engine recovers from surging idle.

After checking for any possible, vacuum leaks, using carb spray I was not able to find anything.

Moved on to clamping vacuum hoses leading into the intake manifold and or throttle body and found nothing there either.

One last hose that was not thought of previously is the one that leads to the intake air (IA) bypass control valve shown below, it feeds into the air tube in front of the VSA valve component .


I clamped that and blipped the throttle a few times while the car was cold and found that the problem was resolved.

Luckily, I had recently picked up several parts from the junkyard, and this happened to be one of those parts that was included so I swapped it over quickly and the problem has been solved.

After I removed the faulty part, I disassembled it and observed that it does appear to be adjustable, meaning that if one were to know the point at which it’s supposed to close and they immersed in some water at that temperature and then adjusted it until the valve was closed I speculate may make an effective repair; could be the reason why this part is no longer available as just something that could be adjusted

 

Interesting.
Just an FYI & not sure if you have seen, via your research, 619rcr's post regarding the purpose of that whole 'air assist valve' & hoses system; however, it appears it can be eliminated entirely by using a J35A8 coolant inlet/outlet pipe & newer injectors.

He further explains on his thread below starting at post #47, continuing through to #49.
High compression J35A3 / J32A2 rebuild - Page 2 - AcuraZine - Acura Enthusiast Community