Related Thread - possible to turn off the car while driving? - S2KI Honda S2000 Forums
Video 1 - Video 2 - everyone,

I'm currently having an issue with my 2000 Honda S2000 that I could use some help troubleshooting. I've attached two videos to help you visually see what is occurring.

Earlier while driving, my car randomly shut off completely. It is able to start almost immediately after, sometimes with a 1-2 second waiting period before pushing the button. This happens each time after cycling the key from On to Off. I only have one key for the car and no key fob came with it. I've owned the car for a little over 2 months and never had issues until today. The car has aftermarket Recaro seats installed (not that it is pertinent). It has the original dealer-installed security system with a little red LED on the center console. To my knowledge, this is unplugged and not functional as the light never turns on and when you push the button under the steering wheel, nothing happens. I haven't checked, but I'm not entirely sure if the original module for that security system is even mounted under the seat anymore. My key ring contains the key, an AirTag, a key fob for work, and a jet tag—that's it.

I've done some basic troubleshooting, which I'll describe below to help narrow it down, but I was wondering if anyone might have suggestions. The thread I linked sounds super familiar, but the OP never posted the resolution to the problem. I can get the problem to consistently happen anywhere between just a few seconds to 2 minutes max before it'll happen again. I've noticed that when the ignition is fully off and the key is removed, there is no green key light on the dash, leading me to believe it's an electrical issue, but electrical is not my strong suit.

Troubleshooting so far:

• Compression Test
• Alternator Test
• Battery Test
• Starter Test
• CEL Code Test (0 DTCs or Faults found)
• It happens at any RPM range
• It happens whether the engine is hot or cold

Any suggestions or insights would be greatly appreciated!

Thanks in advance!

 

Video 1 -

 

Similar thread from a few years ago may have clues.

https://www.s2ki.com/forums/s2000-un...shing-1187491/

-- Chuck

 

I noticed in all the videos that the dash was still getting electricity. Something similar happened to me about 8 years ago and my valves had to be readjusted.

My symptoms were while driving either on highway or residential roads coming to a stop the engine would cut out and I'd had to start it up again. If the car was in motion the rpms would drop pretty low, and at speed it would still be ok, unless going slow. Issue occurred right around 150k miles for me, which looks like your around that. After the adjustment I no longer had any issues with the engine cutting out

Might want to add that to the list as a possible.

Hopefully this bit of info leads in the right direction.

 

Does the car have OEM ECU, O2 sensors, and other electronic parts? Or have they been modified?

Are there any mods to the engine? Like turbocharging?

Are you getting any CEL codes?

Thanks!

 

no CEL codes at all, no matter what I do.
stock ECU, stock O2 (I just replaced them a month ago with Honda original),
only mods are headers. Test pipe (with defouler), exhaust, and an intake. Nothing else.

spark plugs recently got changed along with coil packs

 

Any chance of bad gasoline or a clogged fuel pickup?

 

Ignition switch. It seems clear its acting as if you turned off key (not all the way, but to accessor position).

If you, or a po, used heavy stuff on key ring, lotsa keys, heavy key ring, etc, this would cause stress on switch.

Basically, switch is losing electrical connectivity on some of its connections.

Turning key off, then on again, cures it, bc it remakes these connections.

 

I wanted to share my thought process for anyone experiencing similar issues.

We immediately started investigating the immobilizer, as it's often recommended as the problem, especially since the key wasn't original to the car. I have a close mechanic friend with advanced Snap-on scanners and a blank second key from when I bought the car. The first thing we did was cut and program a brand new key. We also tested the immobilizer unit with a voltage meter, and it seemed to be functioning correctly based on information from Identifix (I believe that's the name of the software).

We quickly ruled out the immobilizer and determined the issue was mechanical, not electrical. So, I continued digging!

A car needs three things: air, fuel, and spark. Spark is easy to check, so I started there, inspecting the coil packs and plugs. These were perfectly fine and working properly. Since I had recently sucked up some water, I decided to perform a compression test, which came back normal across the board. As a last resort, I took the car to a local performance mechanic for a deeper look. I was out of time and couldn't keep messing with it. After catching him up to speed, he used a borescope to check the intake manifold, cylinder chambers, and everything else. He found a considerable amount of liquid built up in the intake manifold. We removed, cleaned, and reinstalled it, but the issue reoccurred about two minutes later. He checked again and saw the liquid build-up. A quick Google search showed that the only way liquid would get back into the intake is through the IAC valve or Throttle Body, as both systems are coolant-fed (a design flaw, in my opinion).

Based on this, we decided to investigate the IAC first. The amount of coolant that came out was astonishing. Upon inspecting the IAC, we found a crack between the coolant passage and air passage. We determined this was likely the culprit and ordered a new one from Amazon for $40. Unfortunately, it arrived broken on the coolant line. We installed it and did a coolant bypass for the IAC for testing purposes, but the issue persisted. We then performed a fuel pressure test, assuming the new IAC was fully functional. After chasing our tails, we concluded it had to be the IAC. I ordered a genuine Honda-branded IAC from eBay for $85, which took a week to arrive. I installed it, but the issue persisted.

Being more familiar with newer cars with advanced technology (I am a software expert for my day job), I started researching. It turns out there's a reset procedure for the ECU that needs to be completed whenever you disconnect the battery to help it relearn the car's conditions and sensors.

The procedure is relatively simple, and here it is:

1. Turn off everything in the car completely (radio, AC, etc.).
2. Disconnect the battery and zip-tie the positive and negative cables for 5 minutes.
3. Reconnect the battery cables to the battery.
4. Start the car and rev it to 3,000 RPM until the radiator fans kick on.
5. Do not shut off the car; let it sit and idle for 5 minutes without touching anything. Do not give it any gas.
6. Take the car for a very spirited drive for some time.

I followed all the steps above, but the car still had a surging effect, and a new P0505 code popped up. We removed and reinstalled the new IAC, ensuring everything was sealed and connected properly. The surging continued, and at this point, the car had been running and driving for about 10 minutes.

No one on the forums mentioned how long it takes for the car to relearn the sensors, humidity, etc. It took a solid 30 minutes of hard, spirited driving for the car to return completely to normal after all the steps mentioned above. Ever since replacing it with a genuine Honda IAC and completing the relearn procedure, there have been no issues with the car.

 

FYI, the coolant lines to tb are to prevent carb icing. A condition where ice can build up inside tb/intake, similar to wing icing on an airplane.

Can only happen in very humid and cool conditions. Underhood temps usually keep tb so warm icing would never occur. You can leave the tb coolant lines bypassed permanently.