weird rpm
 

I have a 97 accord, 2.2 non v-tech LX model, automatic. I have an issue once every few days while I am driving say down the highway and I just take my foot off of the throttle. When I do that the rpm has dropped quite a bit too where I can feel the car slow down and the engine stumbles some. I don’t notice the rpm, because it does it so fast. Then the rpm will pick back up and it’s like nothing happened. The engine will idle like it should going down the road and if I try to get it to do it again it want. Just does it randomly.
So to try and fix this I have checked the IAC valve, everything works there. I cleaned the IAC valve and cleaned the intake as well (sprayed some carb cleaner in the opening and wiped as much of it down as I could. open the throttle all the way and wiped it down. but it has done it a few times already.
So do any of you guys have an idea to what this could be?
Thanks. Ryan

Idle good?
Throttle cable has a little slack to it?
I don't have a wild guess yet, but it might come to me in a dream tonite......LOL
There's several things going on when you snap back the throttle at hwy speed.
Injector pulse changes, Fuel pressure changes, Timing changes.

Idle is good.
Throttle cable is tight.
Timing is good.
Other than that, it has not done it in a while. Until coming home today. Going 35, I started to slow down for a light and it did it twice. Dropped down to 250 rpm, then came back up to I think 1500. I’m so confused....

Throttle cable isn't supposed to be tight. It needs to have a bit of slack when you let go of the gas pedal.

alright, well i will look at that tonight. thanks

i checked the throttle cable. its not tight. it has a little slack, so now back to square one.

No, not back to square one. You've already ruled out a few things.

Clear something up for me... You're driving down the road, & you take your foot off the gas. The tranny is still in "D" so the momentum of the car shouldn't allow the engine to drop all the way down to idle. Kinda like engine-braking, except you don't downshift.

If you take your foot off the gas AND SHIFT TO NEUTRAL, that's a very different situation; more difficult for the idle-control system.

driving down the road, going about 70mph, i take my foot of the throttle to slow down, the car still in D, the rpm drop to around 500 or so. then pick right back up to whatever they need to be at that speed.
i feel it slightly in the engine when it happens. it feels like when you tap ur brakes.
i hope that clears things up....

It sounds like the auto tranny is jumping into neutral & allowing the engine do drop to actual idle - I don't think it's supposed to do that. But I don't know much about auto trannys, so let's hope someone chimes in.

I've been trying to self diagnose a similar issue.

How about at a light? What if you give it more gas than just a gradual amount to get you rolling? Do the same things happen? Does it sort of stumble and the rpm's drop and come right back up? No issues at highway speed if you keep your foot down? How about on a turn. Does it ever feel like centrifugal force might be a factor? Perhaps the fuel pressure drops? Or maybe a clogged catalytic converter?