I have a feeling my motor is about to go boom boom

[christo]

cross posted from honda-tech
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I've searched, haven't found any straight answers.

99 Si JDM B16 block, mugen headgasket, CTR pistons, skunk2 valvetrain, stock cams, VAFC.

Problem started 2 nights ago after changing my oil then doing some VTEC runs. Revs started to bounce from 900-1800rpm.

Wiped my IACV down and that helped it a little. For the next day the revs went from 1100-1300 and would eventually idle smoothly at 1000, which is still too high.

Today I removed my throttle body, IACV, intake manifold and sprayed them down with carb cleaner. Put in some new NGK copper plugs. Now the revs are back to bouncing from 1300-2000 violently.

Attempted to check the CEL (it's been on since i bought the car, assuming it was from my gutted cat/missing O2 sensor), but no dice. The wires to the ECU are spliced all weird from the VAFC (prev owner).

This stuff may be unrelated... did a compression test: 150 270 180 300+ (off the gauge). I was using SeaFoam carb cleaner. I found one small tear in one of the coolant hoses connected to the throttle body, but I doubt there's a leak there. My compression tester might be busted... doesn't go back down to 0, stops at 30. Everything is fscking broken!

how messed up is my car? anyone out there know how to fix it?

New oddities that I discovered tonight:
-I can start the car without disengaging the clutch
-old spark plugs look like I'm leaning out
(this is what I get for buying a $5000 Si)

[christo]

Prev owner put the protective cap on the negative terminal instead of the positive terminal.

You all should've seen me lean against the battery and shock the shit outta myself.

[mpg9999]

Step one: Get another compression tester. No point in looking for other problems if you know thats an issue. Did you notice any lack of power? With two cylinders at nearly half of the other two, you should have noticed something.

-Mike

[christo]

actually after the oil change, new plugs, and carb cleaner the car feels stronger than before and even then it felt strong for a B16.

the only thing that really "feels" wrong right now is the bad idle, I would've thought my compression was fine.

[.RJ]

Did you pull the ECU fuse and hold the throttle wide open when you did the compression test?

[Andy]

I have a obd2 scanner to pull/erase your codes. I thought bouncing idle was a pretty common problem among hondacura owners. IACV or vacuum leak seems to be the culprit most of the time.

[.RJ]

Will that OBD2 scanner work on a miata?

[Sijray21]

Will that OBD2 scanner work on a miata?

should work on any car with obd2

[.RJ]

Well I need to borrow that thing then

[Sijray21]

Well I need to borrow that thing then

if you can't you can always "rent" one free from autozone

just use cash though, i think it's a 180 deposit and you get it back when you return it.

i did that when i was out in cali and the CEL blew.

[christo]

Did you pull the ECU fuse and hold the throttle wide open when you did the compression test?

...oh crap I'm supposed to have the throttle wide open!?...

*bangs head on desk*

[christo]

but anyways... should i just replace my IACV?

[mpg9999]

but anyways... should i just replace my IACV?

You shouldn't do anything until you verify you have good compression. The numbers still look wierd to me, unless you held the throttle open for two of the cylinders, and not the other two.

If the compression checks out then there a million and one things that can cause a wierd idle. Personally I'd start with stuff thats free, like looking for a vacum leak.

[Andy]

Well I need to borrow that thing then

Whenever, I could bring it to Summit in two weeks.

Vacuum leaks suck big balls. Good luck. IACV's are hella expensive so definitely verify that it's bad before you replace them.

[christo]

new compression numbers are
130 275 150 275

I think my compression tester is working somewhat correctly... just doesn't go back down to 0 on reset. gonna check for leaks

[.RJ]

Drop a *tiny* bit of oil into the cylinders and re-test. Test in a different order, to make sure your gauge isnt f'ed up.... you are pulling the ECU fuse, right?

[BLINGMW]

I'm sorry, but those wacky high #'s (275-300) are.... well... WAY HIGH aren't they? Like, impossibly so?

[.RJ]

Honda motors actually have compression chan

Not like the 8:1 slugs in your 98hp beast!

[christo]

wait... let me get this straight... I'm supposed to pull the ECU (40A) fuse? ... I've been pulling the 15A FI fuse...

[christo]

People are telling me that there are 2 holes in my throttle body, one to the Fast idle valve, and the other to the idle air control valve. I've only got one hole... looks like it's for the IACV. When I plug that hole with my finger, the car idles at a steady 800rpm, left open, it starts to bounce.





assuming that's my TPS sensor...

when unplugged, the car idles at a steady 2000 rpm.

I'm not sure that it's a vacuum leak because when the TPS is plugged in, and I start up the car, it idles at 1300 or so. If i blip the throttle at all, THEN the revs start to bounce. So if I start the car up and don't touch the throttle, it'll idle steady at 1300.