Dremetos

My 98 hatch with 100,000 miles is having the piece of **** IACV malfunction code.

The air charge sensor is fine.
ZERO air leaks anywhere.
Coolant is full and has been bled.
TPS doesn't seem to have any issues.
IACV has been cleaned and re-installed correctly.

I can drive the car for anywhere from 20-60 miles and it runs GREAT! No issues at all, idles and pulls like a dream. As soon as the CEL clicks on the car idles at a constant 1500 RPM, and when you let off or tap the gas the car bucks like crazy. I'm completely lost and want to end smash this car with a hammer. I literally drive around with my OBD2 scanner and erase the code to make the car run flawlessly when the car ***** itself.

I need help because I'm at the end of my whits. Thanks guys.

Edit: Could it be a bad throttle body gasket, and when the computer detects the vacuum leak it kicks the CEL on and tries to compensate, thus resulting in the high idle? I have a new one and I'm going to throw it on tomorrow.

Former User

What is this^?

Test the ECT sensor and the TPS.

slowcivic2k

You have an electronic malfunction of the IACV system. You have no power to the valve, no ground, or the solenoid is now an open circuit. This is NOT a mechanical malfunction at its root. That would have to be Idle system range/performance, which it is not.

Since you describe this malfunction as an intermittent condition, check the condition of the electrical connector pins for deformation, corrosion, or weak connection.

Former User

You're confusing P0505 with P1508/P1509.

Dremetos

The air charge sensor is a sensor that plugs into the airbox on the d16y7. I've had it give me issues on other Civics.

Anyway, how do I go about properly testing the ECT and TPS with a multimeter? I want to do it once and do it right. Thanks for the guidance so far. Is there no chance of it being a mechanical malfunction due to the fact that it's intermittent and controlled by the CEL, per se?

slowcivic2k

All of those codes refer to an electrical malfunction, not a mechanical one.

Dremetos

Upon removal of the IACV for cleaning all sensors appeared to make a solid connection and click in firmly, however, what do you suggest I try, another IACV? Are you implying my connector on the IACV is damaged, or that the connector wire itself is damaged? Thanks again.

Former User

The IAT sensor generally would not cause an idle problem or throw code P0505.

When the engine is fully warmed up, unplug the ECT sensor and measure the resistance across the two terminals. It should read 200-400 Ohms.

Back probe the Red/Blk and Grn/Blk wire terminals of the TPS connector. Turn key to ON(II). Measure voltage with the throttle closed (0.5V) and wide open (about 4.5 V).

Former User

Sorry, but this^ is wrong with respect to the IACV. Only P1508/P1509 are IACV electrical malfunction codes.

Dremetos

Alright, I'll be sure to do that tomorrow. My guess also lies on the idea of it being a sensor because it simply makes sense. Just trying to add to my to-do list, if those sensors appear to be functioning normally, where should I go from there?

slowcivic2k

A problem with any other sensor will cause a code related to that sensor, not the IACV. As the IACV cannot be accurately controlled without various inputs, such as throttle angle, coolant temp, etc, an IACV related code can only refer to the IACV circuit itself, which, will refer to a P0505 if using a generic scan tool. P1508 and 9 are Honda specific codes, there is no difference between them.

Honda triggers the IACV from the ground end, so ensure you have source voltage to the sensor connector. If that checks okay, I would substitute or test the IACV. If this does not fix the problem, substitute the PCM, as the PCM may not be grounding the IACV due to a defective transistor.

Former User

You're off target. Please refer to the 96-00 Civic service manual.

A carbon clogged IACV will throw P0505 (mechanical issue) but not P1508/P1509. Conversely, a problem in the IACV circuit (electrical issue) will throw P1508/P1509 but not P0505.

Therefore, your advice quoted below is wrong:

slowcivic2k

http://www.obd-codes.com/p0505

Tell me what part of that document is mechanical. This applies regardless of vehicle type.

Former User

Why do you post a link to the generic description of P0505 when the car under discussion is a 98 Civic? The premise of your argument because null and void as soon as you read the troubleshooting for P0505 versus P1508/P1509 in the relevant 96-00 Civic service manual. Have you looked?

slowcivic2k

Because the code he posted was P0505.

You can look up both of the other codes they mean the same thing.

Former User

This debate is over until you have read and understood the distinction between P0505 and P1508/P1509 in the 96-00 Civic service manual. After you do this, your error will be clearly evident.

slowcivic2k

P1508 and P1509 are not the trouble codes he listed, P0505 is, to the OP, diagnose what code you actually have. I am retiring from this thread until you bring forward results.

Dremetos

Anyway! I'll be running tests on both sensors tomorrow to ensure their functionality. If the problem persists I'll order a new throttle body to eliminate that, the TPS, and the gasket, as well as the IACV (likely from a low mile junkyard vehicle to save money, I planned on swapping this turd come spring, just need it to pass inspection.)

However, if a sensor proves to be malfunctioning (hopefully my case!) I'll jump right on that. Results posted tomorrow.

Former User

You have given bad advice in this thread because you are too arrogant to read the Honda Civic service manual.

Former User

By the way, the ECT and TPS tests I mentioned only yield useful information when P0505 is thrown and the engine is high idling.

Dremetos

Haven't erased the code yet. Car idles at 1500 steady with a warm engine and is throwing code P0505 IACV malfunction, so sounds like we're right on point.

Former User

Good. This^ makes diagnosing easier. Before you test the ECT and TPS, remove the air intake system when the engine is high idling, and then use your finger to cover the hole inside the TB leading to the IACV. Does the idle speed drop?

Dremetos

I'll let you know if it does tomorrow as well. I'll check all three things and report back. Crap luck for me, I bought this car not even a week ago and it needs to be inspected soon. Looks like I'll be riding a rejection sticker until this is sorted. Yikes. At least the car is clean and tidy in all other aspects.

Hoping for a sensor failure to be evident, but we shall see come tomorrow.

Edit: What should I go about doing if the idle DOES drop when I cover that hole inside the TB? Does that indicate a failure in the IACV?

Former User

If the idle drops to normal or lower, then this rules out a vacuum leak, indicating that the IACV is causing the high idle by bypassing air to the IM. This bypass could be caused by an IACV mechanical malfunction, misadjusted idle speed, or a problem with ECT or TPS circuit.

Dremetos

Alrighty, sounds good. I'll run all three diagnosis tests and see where it takes me.