Interesting idle surging - only when coasting in neutral, stops when parked

[belize1334]

The speed sensor is a binary detector that just blinks every time the cable turns. If the symptoms change when the vehicle is rolling then I'd say the speed sensor is working or else the car wouldn't "sense" the rolling condition and there'd be no difference.

When the car is rolling the ECU will keep the rpms up at about 1100 in anticipation that you may reapply the gas or else depress the brakes. It's basically anticipating either dip-in or load and it doesn't want the rpms to be too low when that happens. It's possible that your BISS is adjusted too far in so that the ISC is all the way open just maintaining the 800rpm idle and that asking it to maintain an 1100rpm idle is just asking too much. It can't lift the engine up that high so it starts wigging out.

Go through the procedure for setting your idle correctly. And I HIGHLY recommend getting a block-off-plate to disable the FIAV while leaving the ISC in-tact. The ISC is more than capable of handling cold-start situations and you'll appreciate the simplification of the coolant system when you don't have coolant lines running to the TB. Once done, the ISC is the only game in town so diagnosing the surge becomes alot seasier.

 

[moidsm1]

I had this problem too. I did the un-preffered method. I cut the reed switch wire at the ECU. So now the ECU never knows when the car is rolling. Im not sure if this was the best thing to do but it cured the surge while rolling in nuetral.

Also with my Hyundai Excel 4G63t swap, and an older Mighty Max Swap I never connected the reed switch. The Cars seemed to run just fine /ubbthreads/images/graemlins/smile.gif

 

[PreskitVR4]

Quoting Lonewolf64:
Have you unplugged the ABS computer situated in the trunk? If you have eliminated ABS but it is still plugged in it will cause this exact problem.


That gold box in front of the fuelpump access panel? Damn! My abs is so gone, it looks OE

 

[Lonewolf64]

That's the correct box. Upon unplugging that the issue was solved in the case of 116 and 889.

 

My car is completely stock. I haven't had any chances to troubleshoot it further but I think it may actually be surging when driving partial throttle as well.

Although faint, you can feel the car jerking a little when driving at partial throttle. So this would seem to be more throttle body /tps related to me, what do you think?

 

[1990ggsxnj]

Part throttle that may be the case since it should see the throttle as opened and closed throttle position circuit should be open as well. If you ever disconnected the Closed Throttle switch while surging you would see this just lets the engine idle as high as the air going in will let it because the ECU thinks you're trying to apply throttle. This does not take care of the issue of surging while the throttle is closed but you are moving while in neutral.