i have a 95 cx w/ a b16a3 in it and like 2 months ago it started to get this bad idle problem. when i first start up the car it idles perfectly at 1800rpm and slowly drops to about 1000rpm after about 5 minutes...then all of a sudden it starts to surge from 1100-1900rpm and does not stop that. the things i have tried are different IAC's, checked for vacuum leaks (none), bypassed the cold idle valve, and it is not throwing any codes. any ideas??? a friend of mine said to put on different IAC, reset the battery and let it idle for 15 minutes without touching the throttle...we didn't do that when we first changed the IAC, just put it on and started it. let me know what you guys think...this problem is very annoying. thanks

 

Check your intake manifold gasket. Spray some carb cleaner all around that area (if you can get it underneth) and see if it changes your idle. If it does. There's your problem.

 

tried that...we sprayed carb cleaner all over all the vacuum lines and nothing changed
thanks for the reply...keep them coming

 

Is there enough slack in the throttle cable? You didn't try tightening it, did you? If the TPS is offset, it could cause the surging. Might be worth checking out.

Is the coolant level where it should be and there is no air in the system? An air bubble could trick the TW sensor into sending false cold engine temp information to the ECU.

 

i'll try that...i was thinking that it was something related to the coolant system.
thanks for the replies, keep them coming

 

just bleed the coolant...still has the surging idle
any other ides?????

 

i think you may find that it is you throttle position sensor (TPS)...

this may need to be ajdusted to factory specs again. (0.5v at closed throttle)

have you done anything around the TB to affect this sensor?

hth,

t..

 

Try spraying the entire intake manifold area (not just the gasket mating surface) with car cleaner or 2+2 just to check for vacuum leaks.

If not, then it is your IAC (idle air control) valve.

 

Same problem here. If I take off the IACV and spray carb or brake cleaner thru it, it takes car of the problem for a day or two. Need to get off my lazy a$$ and get a new one.

 

Same problem,
I pulled off the throttle body, cleaned it out.
Didnt fix it.
Pulled it off again and under the throttle body theres the piece with hose connected... forgot the name... connected by 3 bolts, pulled it off, opend up the back, and there was a screw there that had come out. Screwed it back in and sealed with silicon sealent. That cheanged the surge. It used to surge almost imediatly from 2-3k now, it doesnt start for maybe a minute and a half and surges from 1.5-2.5k
I didi that last night, Ill pull it off again and see if I missed something today since that seemed to help a lot.
After that, I pulled off the iac, cleaned the intakes. Seemed to slow the surges?
maybe...

 

i think you may find that it is you throttle position sensor (TPS)...

if not, im not sure.

test it and see...

t..


[Modified by tinkerbell, 8:07 AM 3/1/2002]

 

How do you remove and or test the TPS?

 

depends on how it is attached, not sure on the A3's

the TPS is the black thing that sits on the opposite side of the TB to where teh throttle cable attacches and sends a signal to the ECU telling it where teh throttle blade is at.

it is vital that the TPS tells the ECU that the trottle is closed when it is closed so it goees into "idle mode"

to test that this signal is 0.5v when throttle is closed, get a voltmeter and attach the negative to ground and measure teh voltages of each wire comming off the TPS.

one wire should be 0v one should be 5v and the other should move from 0.45 to 4.5v from closed to wide open.

i use a sharp pin carefully stuck into the wire as a test junction...

to adjust it loosen the bolts holding it on and rotate it to show 0.5v at closed throttle (this is where you may have issues - the bolts may not have proper heads on them...)

i hope this helps.

t..

 

Well your friend was correct by telling you to disconnect the battery... if this didn't correct it, then it would pretty much rule out an ECU corruption problem...

As long as nothing was removed/re-installed prior to this problem, I think I would rule out a vacuum leak..

common causes for fluctuating idle..

Vacuum leak
IAC
Coolant level

And the 2 things you havent mentioned yet..

Coolant temperature sensor
Intake air temp temperature sensor

 

check the FITV (fast Idle thermo Valve) I've heard this goes bad often and when it does it causes a up and down revving idle like your talking about. just a thought have your timing checked too. I had a bad idle problem and it was actually my timing believe it or not the cams were a little off.

 

i have tried the FITV...that didn't change anything. i'm going to try the IAC's again today. i don't know if this would affect it, but i have a bad thermostat...the car will barey heat up, but i do have one on order. thanks for the replies

 

Thanks for replies, Ill try those last ones

 

Do this (hot engine)- tighten your idle screw all the way down- unplug your idle air control valve- remove the intake piping from your throttle body- start engine. Locate the two ports inside the throttle body (before throttle plate) and plug them with your fingers. Does the engine die?

 

Yes Engine Dies. Whats this mean?

TPS is good thanks for info on checking it.

FITV is what I fixed that changed the surge from constant
(as soon as I started the engine 2-3 k)
To only starting about a minute later (1-2k)

btw engine is D16Z6

Thanks

 

that means that air is not leaking past the throttle plate. what is the idle speed with the IACV disconnected and idle screw fully closed? it needs to be around 500 rpm- can you set it to this?

 

Fixhondas, so is there suposed to be a small amount of air leaking past the throttle plate or not. Just wondering, was that a good thing that his engine died when he pluged it up or is the plate in need of an adjust.

 

take a pair of needle nose pliers and pinch off EVERY vacuum line going to the engine. Some to pay special attention to are: pcv valve hose, brake booster hose, crusise control hose....just pinch them all. Actually before I did that I would change the thermostat. Idle is temp. related...could be the problem. Do yourself favor and use a Honda thermostat. Every time I have to use an aftermarket thermostat at work I end up doing it twice. GRRR

 

i am having a similar problem with my car it just started tonight,i am extremly confused and frustrated.my idle jumps up then down just like if you were to remove the idle screw completly but its in tight,i am not sure what caused the idle surge and i am curious on how to fix it....

 

it is supposed to die with those ports plugged off with your fingers- can you get the idle to 500 rpm with IACV unplugged?

 

Just remember, before you go adjusting your TPS, clean your throttle chamber to be sure it's not a build up of carbon that is causing the throttle plate to be off slightly. I've run into that on even low mileage Hondas.