rujoesmith

98 civic ex, d16y8, manual trans, 150k

Ive been having problems with a jerky accelerator and poor idle for quite some time. The CEL code i keep getting is "P0505 Idle air control system"

things ive tried:
replaced IAC valve
removed and cleaned throttle body
thoroughly bled cooling system

According to the scanner, when the car is at idle the "absolute throttle position" is 9.4% and when the pedal is fully depressed it is only 89.8%. Is this normal? it would seem like it should range from 0-100. Another thing i noticed while cleaning the throttle body is that the throttle plate doesn't seem to close all the way. Its at a slight angle and is definitely letting a little air through when its just sitting there.

Any ideas what could be wrong? I just cant seem to figure it out

Thanks!

ezone

Yes that sounds about normal, but reading the actual voltage would be better.

If you were to actually measure TPS sensor output voltage with a voltmeter (or a scanner if it will read in volts) it should begin at 0.49v (most are set at exactly 0.49v closed throttle) and as you slooowly open the throttle by hand the voltage should rise smoothly up to around 4.5ish volts at wide open throttle.

If the TPS voltage is reading much above 0.50v it may be slightly open? If someone has messed with the throttle stop it may be. It should close far enough to block almost all of the airflow yet still be open far enough to not stick and jam in the throttle bore.
If nobody has messed with the throttle stop it should be ok as the factory set it.

What does the crummy idle do? Too low? Too high? Rough? When did it begin acting bad?

Is the idle speed too high right now?
Plug the port inside the throttle body with your fingers. Does the idle speed drop a bunch? Does it stall or almost stall the engine?

Vacuum leaks, sticking IAC, stuck open throttle blade, inaccurate ECT and/or TPS

rujoesmith

it idles at about 1500, and jumps between about 1500-1600 super fast. But the lurching doesnt really start until the engine heats up