Uncle Ben 1

I am having some intermittent idle issues on my Accord that come very close to stalling, but it has never stalled on me as of yet. It is a 2001, 4cyl, with about 135,000 miles. Generally the engine runs very smooth with no power issues and no missing, including at idle, but every now and then it will idle low at about 600 rpm (according to the dash gauge), but even at that low of an idle it still feel fairly smooth and is not shaking or feeling like it will still...so that is one issue, since it seems that it should be idling in the 750 rpm range.

The larger issue is that sometimes the engine will nearly stall, with some shaking, but it never actually stalls. When it does this it will typically dip down to around 400-500 rpm and then come back up on its own, or I'll rev the engine to make sure it does not stall. In nearly all cases, it only does this when I come to a fairly sudden stop, like in traffic or when coming up to a red light. Not as severe as slamming on the brakes, but just a somewhat quick stop as opposed to a regular/slow stop.

Today in traffic when I came to a quick stop on the highway, the RPM dipped all the way down to what appeared to be 100 rpm at the very bottom of the dial. The engine shook as expected, but I pushed the throttle and kept it from stalling.

What are some possible causes for this, and what tests can I do to diagnose this? Thank you!

jdowen2

Have you done any maintenance? Clean the throttle body, IAC, and EGR for starters.

quintb2000

Does the problem occur when the engine is under a load such as when the compressor is on?

Uncle Ben 1

I will definitely clean the throttle body since that has never been done, but can you help direct me to some diagrams or something that would help me locate the IAC and EGR, and the procedure for cleaning them...

Uncle Ben 1

I removed the intake and cleaned the throttle plate and bore, and also the IAC. After putting it all back together and starting up the car...there is a huge problem. Not only is the engine not running better, it is far worse, to the point of being un-drivable.

As soon as he engine is started up, it revs itself up in a continual pulsing pattern. It revs up high (4,000 rpm) and then goes back down every 1 or 2 seconds. It is so bad that it is completely un-drivable. It is also making some type of whining noise along with the engine revving that I have neve heard before.

Due to the IAC being right against the firewall, and the mounting bolts facing the firewall, I had to remove the air intake and all the various vacuum hoses and electrical connectors, but I labeled them first to make sure I put them all back in the correct place, and I have checked many times to see if there was anything I forgot to connect or connected to the wrong place, but I can't see any issues.

my scanner is showing P0113, "Intake Air Temperature Sensor 1 Circuit High"

Freeze frame data says the intake air temp was -40 (I live in CA and it is over 50 right now, far from a negative temperature. Engine coolant temp 71. Fuel system status says "Open loop due to insufficient engine temperature".

I tested the ITC (intake temperature sensor) and I'm getting the following readings, which seem to be correct, but please let me know if I am interpreting the ohms incorrectly (I sometimes confuse the readings on the multimeter)...
on the 200k scale: 003
on the 20k scale: 2.5
My repair manual says resistance should be 2,500 to 3,500 ohms with the connector removed and the engine off.

I also removed the ITC and bench-tested it according to the manuel, which says to heat the sensor with a heat gun and that the ohms should lower to about 250 ohms at 180 degrees f. I don't know when I reached 180 degrees, but I do know that the ohms dropped quickly as the heat gun got warmed up. To me it would appear that the sensor is fine, but then why would I get P0113 code?

Thanks for your advice!


(quint: I forgot to answer your question above. As far as I know, it does not occur when the engine is under load, particularly since my AC is not working, so it is never turned on)

Uncle Ben 1

FIXED! It was a vacuum leak at the back of the plenum, against the firewall. A metal hose supporting bracket was pinched between the plenum and the intake when I bolted it back together. I found it by doing a smoke test. I had no idea a vacuum leak could cause idle issues that severe, to the point of being non-drivable. No more check engine light or trouble code either.

Driving the car to work today I could see that the original idle issue that prompted me to clean the throttle body and the idle air control valave is now gone. It is idling at about 750rpm, right where it should be.