2003 Pilot Idle Surge Hell (P0505)
 

So I've searched the web (and then some), racked my brain, and have tested the shit out of everything I can think of to solve an idle surge.

Vehicle: 2003 Honda Pilot

Symptoms: When the car warms up (NOTE: This car does NOT have a fast idle valve, just an IAC valve) the engine revs up and down from 1000 to 1800ish rpm endlessly. It sets a code (P0505, idle air control system malfunction).

What I've tried/looked at:

I have tested the TPS sensor voltage. .45 volts closed/4.5 WOT. All in spec. I've even replaced the TPS (yes I adjusted it correctly) with same results.

I replaced the IAC valve itself. It got "better" as in when I replaced the valve I reconnected the battery and waited 5 minutes with engine idling to learn the idle (referred to in Honda land as the idle learn procedure). The rub here is the car idle freaking perfect (650-700rpm) right after this, but the minute I pull it out of the garage and go for a 2 minute drive, wamm...back to surge land.

So here are my next thoughts:

I've sprayed a metric ton of throttle body cleaner looking for vac leaks. None found (yet). I put my finger over the IAC-V hole in the throttle body. The idle settled down but did not kill the engine (NOTE: I only used my finger which isn't the best seal of course).

I am planning on:

Bleeding cooling system (in my opinion it shouldn't affect this as the coolant to the single IAC valve is only for heating purposes/read: no wax pellet fiav type crap) as I read several articles pointing to that being a possible coolant temp sensor nightmare resulting in this.

Putting a nice thick piece of duct tape over the iac-v hole to see if the engine will stall out (thinking vac leak test). Of course I could/will try to put my hand over the throttle body itself as this SHOULD kill the engine assuming no vac leaks.

Full disclosure: I had this POS car at the dealer a few weeks ago for diagnosis of an SRS system issue (entire ****ing srs computer that I replace for $90 versus the $699 the dealer wanted of course) and they "diagnosed" the idle issue as "Saw TPS voltage high, internal failure of throttle body recommend replacement". This is puzzling as I stated that I measured the tps voltage at idle and it was the correct .45 volts. Is it POSSIBLE that the throttle body itself is not closing 100% of the way? Visually it looks "ok", however I figure if the iac-v hole with tape test doesn't stall the engine that I could try spraying right into the throttle body blade itself to see if anything gets past it when theoretically closed.

ANYONE who can provide assistance is seriously appreciated.

Re: 2003 Pilot Idle Surge Hell (P0505)
 

UPDATE: I bled the cooling system (no air, but hey I ruled it out).

I put my hand over the throttle body itself. Car stalls. No vac leak after TB I would say!

I then completely sealed the IAC-v hole before the throttle blade with duct tape. Car idles perfect. I then sprayed throttle body cleaner at the closed throttle blade (while iac-v hole was sealed closed). Car stalls. Possible issue with throttle body valve itself!?! I'm not sure how "sealed" a closed Honda TB is supposed to be.

Anyone? I'm left with:

Bad throttle body itself/replace the whole TB

Or

Bad IAC valve from Autozone

Thoughts!?

Re: 2003 Pilot Idle Surge Hell (P0505)
 

Just for a final test:

I checked TPS during issue/surging. TPS voltage is rock solid .50 volts before and during issue (which is acceptable).


Bad IAC or bad TB itself? Anyone?

A POSSIBLE scenario is a bad sensor elsewhere in the car commanding the IAC-V to go nuts. The only one I can think of is the coolant temp sensor in the bottom of the radiator itself. I had an issue with that one (keeping key-off fan on forever), but that doesn't happen anymore. Is that sensor part of the idle equation?