Hmotoredcoupe

I have a 99 civic dx with the d16y7 (intake manifold has throttle body one top)
The problem started yesterday and I have searched but do not want to replace unnecessary parts.

I have no cel on. On a cold start the car idles high, then begins to surge as it warms up. Driveability is normal. Once it gets warmed up the car begins to hesitate when I shift and at low rpms. I do not have a tach but guessing around 3k it clears up and drives normal when accelerating, but it starts bucking when trying to cruise at a certain speed. I am lost.

So far I replaced the fuel filter, which did not change anything. I was lower on gas yesterday when this began so thought maybe I sucked something up.

I scanned it for codes at work and a iacv code came up. I know this can cause the idle surge but wasn't sure if this could also be causing the bucking? I do not want to buy a 150 dollar part for nothing. I tried to clean it by spraying throttle body cleaner in the hole in the throttle body for the iacv but it didn't help any. Should I take it off and clean it?

I also read that a bad tps could cause an iacv code, but I checked it with a volt meter and it is a .5v when closed and 4.6v when wide open. So that checked out ok.

No noticeable vacuum leaks.

Anything else I should check before spending the money on an iacv? Couldn't it possibly be an intake manifold gasket? Do not know of anyways to check it though. Possibly o2 sensor? Any ways to check this?

goldsy

An O2 sensor would throw the CEL on for sure. I can't really see the IACV being related to the bucking but to clean it right, take it off. Soak it with throttle body cleaner, brake cleaner or simple green. Either one will so the trick. Spray it until dirt stops coming out then scrub it with a toothbrush. I don't recommend brushing your teeth afterwards. Spray it some more. Make sure it opens and closed properly, reinstall it then bleed the air out of your cooling system because you introduce air into the system when you take the 2 coolant lines off the IACV.

I had the same issue with my IACV with the surging idle and my CEL did not come on.

B_Swapped93

have you checked the TPS with a multimeter to see that it's to spec .45 closed 4.5 open and to see that you don't have dead spots.

https://honda-tech.com/forums/tech-misc-15/diy-how-calibrating-voltage-your-tps-sensor-2947986/

Hmotoredcoupe

I will try taking it off and cleaning it better tomorrow.

I have already checked this. It was .5 closed and 4.6 wide open. I opened it slowly and it read all the way through with no dead spots.

Hmotoredcoupe

Well I cleaned the iac tonight. There was some gunk built up in it and it did not want to spin all the way around, soaked it with throttle body cleaner and freed it up. Idle surging has gone away as well as the hesitation/bucking when driving! But I did notice after I pulled it in that I had a little puddle of gas underneath the tank now... On to the next one problem!