BeaterHonda

I just did a complete tune up on my 94 Accord (non VTEC). I put in a new timing belt and balance belt, plugs, wires, hoses, coolant, the works. I also cleaned the throttle body with carb cleaner...

I fired it up once it was all together and things seemed to be ok, until about a minute of idling, it started surging between 1200 and 1700 rpms, alternating continuously. I double checked all my connectors, vaccuum hoses, and wires, etc, but did not find anything to explain this.

I took the car for a ride to see if it would settle itself, and the problem seems to go away when the car is in drive or in reverse, so it only surges in park and neutral.

I did some searching and some people said it could be the fast idle thermo valve... so i took off my throttle body and looked at the FITV, and it seemed ok tooo, nothing out of the ordinary. it seems to be just a plunger type valve, so what would cause it to do this in only park and neutral but not drive or reverse?

What else could i check out? Should i try resetting the computer? Why would this problem happen after the tune up?

Thanks!

F22B Prelude

If you did the coolant flush yourself i bet you got some bubbles in the line

If not search for IACV

BeaterHonda

Hello,

I'm actually doing some reading now, and i'm going back outside to try burping the coolant a little more (i only left the radiator cap on before, i didnt use the bleeder port)... and then i'll try to take the IACV off to clean it more.

Out of curiousity, why would air in the coolant mess up the idle? Is it because it confuses the fast idle thermo valve?

Thanks for the quick reply!

gulfview

Other possibilities:

an air or vacuum leak

a defective throttle position sensor

a bad MAP sensor

BeaterHonda

Thanks for the replies.

Update... I did some searching and found out how to adjust the fast idle thermo valve, so i did just that... took it off, screwed the plunger all the way in, put it back on the car, and fired her up.... but still surging like before. So i did the following things:

1) bled the air out of the coolant

2) adjusted the FITV

3) checked for vaccuum leaks using unlit propane torch.. found no leaks

4) checked TPS as mentioned above... TPS is good- .488V at fully closed throttle, then 4.3 or so at full open blade

5) made sure all the bolts were tightened for the TB, IACV, and FITV, and the intake to the engine itself

5) i had the inlet tube off the whole time... i did some testing with the two ports on the side of the TB... when the car is warm, it is still surging. but when i put my finger on the upper port (the one for the IACV) the surging goes away. I took the IACV off and put 12V accross the terminals, and it clicks just like its supposed to... I then unplugged the connector to the IACV, and it reads 12V to ground.

When the car is warm, is the IACV supposed to still be sucking air into the intake?

So correct me if I'm wrong, it seems like something is activating the IACV when its not supposed to (i checked voltage to the connector and its reading 12V when its surging) and its making my idle bounce up and down by giving the engine too much air????

So what controls the voltage to the IACV? Is it a sensor or something? Can the IACV be bypassed, and what are the effects of doing so?

And also the surging only happens with the car in Park or Neutral!!!

Please help, i'm at my wits end, i'm thinking of driving it into a river, or just bringing it to the dealer!!!!

BeaterHonda

Another update.... after going inside for a little bit to cool off, i did some more searching on this site, and found some people who had this problem fixed it by replacing the MAP sensor.

So i went outside and probed the sensor like what the Haynes manual says... it checks out at 4.97V to the connector when it is unplugged, ignition in "on" but not started. When i backprobe the connector like the book says, i read 2.88V.

But when i start the car, and read the voltage at this connector, the voltage does not increase with more throttle... While the engine is surging up and down, the voltage goes between 1.9 or so, down to .9V, and when i open the throttle with my hand, voltage goes to .9 or so and does not increase with throttle.

Finally, while the car was running and still surging, i unplugged the MAP sensor connector, and the car stumbled like it wanted to die, but then started idling normally, with no surging or bouncing up and down, as if the car was running like it was supposed to.

Does this sound like a bad MAP sensor? If so, will replacing this solve the up and down, bouncing idle problem? PLease let this be it so i dont need to take it in to the dealer!!!

And oh yeah, while i was at it i took gulf's suggestion and took the EGR valve off and cleaned the carbon out of it and reinstalled it. looked clean, but did not solve the problem...

Sorry for the long posts, and thanks again for the replies!!!

stereo

if this all happened after you did the timing belt double check the timing on it if off a tooth it will surge but first bleed the system as if theres air pocket it will surge just like you describe and sometimes it's they are just stubborn and won't bleed out.

gulfview

Yes, a defective MAP sensor is a common cause of idle problems. You can buy used ones on eBay usually.

BeaterHonda

I have good news!!!! I was in town visiting my parents, and my uncle was there, who has a 1995 Accord LX 4 cyl. I took his MAP sensor off and put it on my car, and voila! no more bouncing idle! after i started the car, the idle settles right down to 600 rpms or so, right where it should be.

So i'm on the hunt for a MAP sensor now, but at least the problem is solved!

Thanks to everyone for the replies, especially you gulfview! i saw your write up/step by step procedure on how you fixed the bouncing idle problem and it fixed mine too!!!

Thanks again and happy new year!!!

gulfview

I am really happy for you, BHonda. Good work!