My firend just got a 94 Del Sol w/ a b16a swap and AND GSR tranny, Anyway when he starts it up it idles at 1,500 RPM then goes down to about 800 then shoots back up to around 1,500-1,800 stays at that for a little bit then falls back to 800....it repeats this process over and over again, even after being run for a while
Does aybody have any idea of what this could be?


Thanks Chase

 

My car did the same thing when I first swapped in its second engine. Disconnect the negative battery cable, this will reset the ECU. Then start it back up, and once the idle starts to jump around, move the idle screw (on the throttle body, usually facing the driver-side fender) in and out a few times, and then set the idle to the proper speed. I don't know exactly why, but this almost always works to solve the jumpy idle.

 

Check your vacuum hoses for leaks

 

either vac leak or a bad IACV

 

do you have the check engine light on ?

 

Another possibility is air in the cooling system. The Honda/Acura IAC (Idle Air Control) valve, or EACV (Electronic Air Control Valve) is mounted up high in the cooling system, but still below the bleeder bolts. Air bubbles trapped in the system tend to migrate to the IAC or EACV.

The IAC (or EACV) does two things: (1) it tells the ECU how hot the coolant is near the throttle body and (2) it provides a passage around the throttle plate to set the idle speed under control of the ECU.

When the engine's cold, the IAC tells the ECU and the ECU tells the IAC to stay open, setting the "cold idle" up high. As the coolant warms up, the IAC tells the ECU and the ECU tells the IAC to close up a bit, bringing the idle back down a tad. When the engine's fully warmed up, the idle should be somewhere around 750 - 800 rpm.

But then, one of those air bubbles comes into contact with the IAC. The bubbles aren't as hot as the coolant, and the IAC reports this to the ECU. So the ECU tells the IAC to bring the idle back up. As the coolant and the bubble slosh around under the IAC, the IAC is telling the ECU, "It's hot. No, wait... it's cold. Wait... now it's hot again..." and the ECU continues to hunt, back and forth, between cold and warm idle speeds.

If this is your problem, try bleeding your cooling system.

 

I can't speak for all models, but in '95 the IACV is totally mechanical. It works on the same principle as the coolant thermostat and actually has an adjustment... Even though it is NOT recommended to adjust it. The IACV reacts VERY slowly, air bubbles in the cooling system should not affect it like that.

My roommate's '90 Accord uses a very similar valve as my '95 GS-R. The Accord does the same thing you're talking about when it's cold. High idle is about 1600 RPM, but it will suddenly drop then raise and so on until the car is totally warmed up and idles properly.

My theory: High idle is set too high... IACV needs to be adjusted lower. I very much dislike the fast idle circuit and defeated mine by closing the IACV as far as I could. Now "high idle" is about 1000 RPM.

good luck!

 

I had just replaced my TB gasket and it fixed this problem, same for a friend of mine who has a B20/VTEC.

 

Hi I just baught my 94 honda accord ex on saterday. but my car was idleing high and some times jumping. try checking your intake gasget it might be leaking. it cost me 8 dollars to get the gasget and mine was trashed. that would be a more efficient fix. it might also help your gas mialige too.