eaf

Hi,

Smth just happened to my 99 V6 Accord after I didn't drive it for 10 days or so.

Immediately after I start the engine, RPM jumps to 2000, and then after a few seconds it continues oscillating between 900 and 1500 every second or so. The oscillations do not stop when the engine warms up: RPM keeps going up and down as long as the transmission is either in "P" or "N" as if I was cranking it with the gas pedal.

The car is still driveable. In fact, on the highway, it feels the same as before, I do not feel, see or hear any oscillations, but traffic lights became a real nightmare: the RPM stays high at 1300, so I really have to step on the brakes to prevent the car from moving.

Once "Check Engine" light came on on a traffic light. I reset it by disconnecting the battery, and it didn't come on ever since, so I successfully drove the car home for 50 miles or so.

Did someone experience anything like this? What could be the problem?

Thanks!

e3NiNe

These are the classic "fast idle thermo valve" symptoms.

Search around and see what you dig up. People will also say "vac leak", so it doesn't hurt to check your PCV valve, because it's only a $3 fix.

98CoupeV6

Hi, welcome to HAN.

Next time you get a CEL, instead of resetting it find out the code (read the FAQ). They don't come on for no reason.

e3 pretty much covered it...when's the last time you changed your spark plugs/air filter?

eaf

Thanks for the replies.

Agreed, resetting the computer was stupid idea, however I had a tiny hope that power reset might revert things back to normal.

Air filter was changed a few months back, but the plugs are not due for replacement until 100k, as far as I know, and I only have 87k at the moment.

About the FITV... Should it be replaced or just cleaned? Are there steps I can take to make sure that it's the FITV indeed?

Thanks again for the prompt replies.

98CoupeV6

Well 100k is what they say, but it's cheap and doesn't take long. I don't run my plugs more than 30k, but I use copper instead of OEM platinum.

Read this for some tips:

eaf

How can bad FITV cause *oscillations* at higher than normal RPMs? I'm reading that inside FITV there is a thermowax, which contracts the plunger, which in turns lets more air enter the engine thus increasing the idle speeds until the engine warms up. If we assume that FITV went bad, and lets the air in even when the engine is warm, why isn't the engine simply running at say 1500rpm all the time? Why is it going back and forth between 900 and 1500?

Also note that the engine is not stalling, it's consistently running at higher RPM than normal. Even though there are oscillations in neutral, these oscillations are still happening in the above normal range. Shouldn't bad plugs and dirty filter cause stalling rather than revving?

98CoupeV6

Osicillations could be caused by overcompensation by the computer. The FITV is not necesarily broken, but it could be receiving the wrong signals from the ECM/PCM. Admittedly I don't know a whole lot about the intake system, but I'd start with the basics first. I've worked on cars with fast idles and PCV Valve, spark plugs and air filter are the cause 50% of the time. If you had restricted air flow or poor ignition, the ECM/PCM would compensate by increasing air flow or fuel flow into the cylinders.

eaf

I collected more info.

Today the "check engine" light came on again, and I got the code this time. It's P0505, which decodes as "Idle Air Control System".

This is very much in line with what you guys already pointed out, however it's not as detailed as I hoped it would be. No clue whether it's FITV, IACV or hoses.

To make things worse, I cannot even find where the FITV is. The snapshots that were posted here in anothread are for some other engine, and mine is 3.0L V6, and, alas, I don't have the repair manual available.

Does anybody have intake diagram for the V6 3.0L?

The tubing scheme under the hood has an EVAP purge value in it. Though the valve is connected to the intake by a hose, it's not attached to the intake: it stands aside.

Other related things that I got from the computer are the:

Intake Manifold Pressure: (11.5 in.hg.)
Abs Throttle Position: 9.8%
Fuel System1 Status: continuously cycling between "closed loop" and "open loop, driving" while the transmission is in the "P".

Any clues?

98CoupeV6

How did you get all this info, out of curiosity?

Here's P0505:

DTC P0505: Malfunction in Idle Control System

NOTE: If DTC P1519 is stored at same time as DTC P0505, troubleshooting DTC P1519 first, then recheck for DTC P0505.


Start the engine. Hold the engine at 3,000 rpm with no load (in Park or neutral) until the radiator fan comes on, then let it idle.
Check the engine speed at idle with no-load conditions: headlights, blower fan, rear defogger, radiator fan, and air conditioner are not operating. Is it 700 ±50 rpm ? YES-Intermittent failure, system is OK at this time. NO-If the idle speed is less than 650 rpm , go to step 3; if it's 750 rpm or higher, go to step 4.
Disconnect the 3P connector from the IAC valve. Dose the engine speed increase or fluctuate? YES-Adjust the (base) idle speed. If it's impossible, clean the ports in the throttle body. NO-Replace the IAC valve.
Turn the ignition switch OFF .
Remove the intake air duct from the throttle body.
Start the engine and let it idle.



Put your finger on the lower port (A) in the throttle body. Does the engine speed drop? YES-Adjust the idle speed. If it's impossible, replace the IAC valve. NO-Check for vacuum leaks, make sure the throttle valve is completely closed, and repair as necessary.

eaf

OK, it turned out to be IAC valve indeed. After replacing it, things went back to normal.

And to answer your question, this info was collected with an OBD-II reader connected to a laptop. On one screen it displays the current error code, and on another it shows the state of some (but not all) sensors.