sprcivic214

I have had an ongoing battle with my 98 civic ex mt stock D16Y8. P0505 came on after driving about month ago replaced iacv and cleaned out TB. Reset codes. P0505 keeps coming on after the car warms up and I come to a complete stop. After cel comes on I start seeing higher idle (not fluctuating) and the car shakes violently when accelerating from low rpms at upshifts.. 4 and 5 gear not as bad, still noticible though. Also after cel comes on if I am not moving and press accelerator engine sputters at low rpms if I gas more it seems normal. Is it possible that tps can throw a p0505... If it is the case honda tells me throttle body needs to be bought as a whole unit with tps already calibrated... 300 bucks my cost. looking for suggestions before I dump 300 in the can.

ezone

Prove the TPS good or bad.
Test, don't guess.

Make sure there are no vacuum leaks.
Reset minimum air rate/base idle speed (if it has the big screw to do this) since you cleaned the throttle body and IAC, then do the idle relearn.

I'd want a lot more info now.
I'd want to see what it's doing myself, and maybe view some live engine operating data on a good scanner. High idle RPM is one thing, but running badly is quite another and doesn't normally happen when it's a simple idle speed problem. There might be something else going on.

sprcivic214

Maybe this video will help explain my problem

ezone

That's "interesting".



Could be TPS related, but could be other things too.
I'd probably see what's going on in a good scanner datalist while this is happening, then make some determination from there.

If you don't have a scanner, I suggest you test and monitor the TPS voltage, see what's going on when the engine acts like this.
Voltage at closed throttle should be ~0.49v every time. Sweep test should be smooth and linear.

(TPS spec is "ABOUT .5v", but 99% of their cars read 0.49v exactly on the TPS, it's darn consistent.)

sprcivic214

Fixed!!!!! Went to my uncles shop and used his scan tool. TPS was working perfect .49 to 4.5 without any lag or skipping. Checked iacv perfect idles at designated temps. Then started from the basics and remembered that my cruise stopped working right before the problem started. The vacuum hose was disconnected directly from the intake. Connected it back and BOOM idles back to 700 and no more jerking.

ezone

Note everything during diagnosis, no matter how insignificant it may seem at the time. This would have been handy to remember about a week ago, right?!?
LOL
The smoking gun!


Glad it's fixed, thanks for the update.