When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Issues with Dropping Idle (lights dim temporarily)
Hi all,
Looking for suggestions on what systems/components that could fail or become affected in warm weather. It is very strange that my engine (B18C - JDM ITR running on a P28 with S300) typically idles perfectly for all of the winter season, but as soon as spring/summer begins and the weather reaches a humid 80 degrees F, my idle starts acting very funky. What I mean is that for almost any entire trip, besides initial start up idle, the idle (after beginning to drive) will drop way below normal and feels like the engine wants to die (but never will). Typically the idle is solid at around 800, but in these times the needle drops to basically 0.
My thought is that there may be a vacuum leak, but I am not aware of these only presenting themselves in warm weather. Does anyone concur?
Basic tune up was done and this did not change the issue [ oil change, fuel filter change, air filter clean, spark plug check (these are PFR7G-11s with about 10k miles on them) ].
Thanks in advance for what might sound like a vague and/or newbie post..
Last edited by Dekorum; Oct 4, 2018 at 11:39 AM.
Reason: add ECU info
So it got a bit colder and the problem still exists. I do not think I need a re-tune.
I did notice that when the idle drops, the lights (inside and headlights) dim. In the following video, I am flicking the gas pedal which makes the idle drop low before raising back up to normal. As I said, this also happens when I am coasting to a red light not in gear (<30 mph). I just changed all of my ground wires, which I thought was the problem but it did nothing.
Battery is good. 12.4 V with a multimeter when the car is off. 14.4 V when the car is on (alternator seems good).
Well, back in 2013 I replaced both the ECT sensor and ECT switch (fan switch) with new OEM. Could the sensor go bad already? I would say 25k miles in 5 years.
No O2 sensor, as the car is tuned on S300.
Not sure if I suspect a vacuum leak. Does the video above make you think so?
You are correct, my OEM ECU is a P28 (OBDI) which has the Hondata socket soldered to it.
I can't be 100% sure that my P28 itself is in good working order. Any idea on how to do that? If not, I would have to buy another P28 and solder a new Hondata socket to it.
I will open it up and check when I get a chance. I feel as though my car would be running much much worse if the ECU were truly bad. The engine still roars like a bat out of hell. Just something funky with finding the idle and dimming all of my lights
It's a random shot I put out there. But I have heard of people having "weird" issues that didn't play out to any of the usual diagnostics only to to learn the ECU was on it's last legs after much work and diagnostics.
I’ve done pretty much nothing with regards to vacuum leaks. Any suggestions? I would think that a vacuum leak is constant and if I had one, I would never be able to hold a solid idle.
I would also do resistance checks on the ICM and ignition coil. I've had 2 each go bad in the last 3 years on Hondas in my family which caused some weird issues. They get heat sensitive or die completely. What year is the engine in there?
Oh, I see.. we are talking about parts 12 (coil) and 8 (igniter) below:
The igniter is about $230 and the coil is about $116. Definitely not cheap parts to replace with OEM.
Pretty sure everything in my distributor is original except for an OEM replacement cap and rotor that I performed during a tune up about 40k miles ago.
Where is the ICM located? Not sure if that is the same thing as the igniter.
The ICM (Ignition Control Module) is the igniter, #8 in that illustration. It has a different name depending on where you go. Have you checked the resistance of both parts yet? Don't just toss parts at it.
Issues with Dropping Idle (lights dim temporarily)
