idle drop and spike 1.6L miata

[smoothiebun]

Hey guys, I'm having an issues with my 93. When i start her up she almost stalls out but idles come back up. I'm thinking its a vacuum leak but can't find it. It maybe along the intake hose from the throttle body.

She also spikes after warm up to 2000 but if i put on the ac she drops to the correct idle. This is leading me to believe its the iscv at the throttle body. While she was idling at 2000 I tried to jump Ten to Grnd but nothing changed. I'm not sure if i did it correctly. I can't pull codes due to my instrument cluster lights all not working, only light that works is ABS, Head light indicator.

I also hear water around the driver side, I'm thinking its water underneath the car so I'll need to poke at the pinch welds to release it. Any suggestions on what to poke the holes with?

[drummingpariah]

I've been hunting down what sounds like the same roaming idle issue for awhile now, and have replaced the iacv (on the bottom of the throttle body) AND air valve (on the engine-side of the intake plenum). I still think there's an intermittent vacuum leak somewhere in there. I even installed Megasquirt to solve the problem, but it's still all the same symptoms (high idle while driving is terrifying - engine braking suddenly stops working).

As for the water sounds, you'll find a lot of FAQ info on cleaning the rain rail drains. A quick search will get you everything you need (with photos and/or video, if that's your preference).

I hope this helps.

[— kung fu jesus —]

For the both of you...

It is common for the 90-93 to develop cracks in the stock intake crossover, particularly around the flexible, accordion-looking area. I would suggest removing that, clean it with warm, soapy water, then carefully inspecting the entire crossover for cracks, leaks, splits, etc. If you articulate the flexible area, it can expose damaged, cracked portions. This can be repaired with simple sealants, or even electrical tape.

Be sure to look at the "J" shaped tube that runs from the intake to the side of the throttle body. The one that is about 3/4" in diameter.

If you suspect the ISCV, try unplugging the electrical connection for it at the front to see if if the idle characteristics change. If not, move on to searching for a vacuum leak. The cheapest way I know is to take a can of ether (starting fluid) and spray short, quick bursts near manifold mating surfaces, intake couplings, vacuum hoses, etc. This stuff if highly flammable, so don't start spraying it liberally around the engine bay. the engine will race a little if the ether finds a way in, locating a leak in the vacuum/intake system.

The ISCV is also very sensitive to cleaning agents so using throttle body or MAF cleaner (NOT carburetor or brake cleaner) is best.

Also test the tension of your throttle cable, check the cleanliness of your throttlebody itselk, too.

[— kung fu jesus —]

Finally, if your CEL light is burned out, you can add an LED or lightbulb to the TEN GND jumper wire to retrieve the code by the number of times it flashes, IIRC. This would be top priority for me, personally.

[— kung fu jesus —]

For the drains in the pinch weld, use a pick tool or narrow awl. You can also use a loose, small drill bit and work it up through the current drains. Be careful not to snap any tool off in those holes.

sb034_94_1 (1).jpg
sill1.jpg
sill2.jpg

[smoothiebun]

would any led work? I just messed with the sills a few moments ago but i read an article that he drilled them to be bigger since they are inadequate. I want to go ahead and do this, and pretty much prime the bottom and paint it so no rust can occur at the source.

My ISCV should be arriving this week so i'll be able to take apart and do a proper cleaning and inspection. If my ISCV isn't the issue, then i'll go see if anyone on the forum may need it. I hold onto my parts just in case someone may need it. As for the intake tube is there anyway i can create a 'costume' intake tube with aluminum tubing found at auto part stores?

[drummingpariah]

It looks like my problem was a bad seal on the block-off gasket on the idle air control valve mounted under the throttle body, which means the plunger inside of it was sticking. I made a new block-off gasket and drove the snot out of it for awhile today, and haven't seen the runaway idle issue any more. I hope my experience helps a little, smoothiebun.

As for intake ducting, you're going to have a challenge trying to create anything custom that does you any good. The biggest restriction in the intake is the AFM (air sensor just before the airbox), so you aren't going to see any gains from changing the ductwork until you replace it. My understanding is that you can use an FC RX7 unit that is a little bigger, but I just switched to Megasquirt and called it done so don't quote me on that.

[smoothiebun]

yeah i looked up some images on 'Costume Intakes' and I just want to get rid of the plastic tubing to cut down on Vacuum leaks. Like in the image, I don't mind having the OEM airbox but i'm not sure where they got that piece. Or Like in the 2nd image just get rid of the accordion piece. Anyways i'll let you guys know what happens this weekend when i get the ISCV and attempt to install it.

[— kung fu jesus —]

My understanding is that you can use an FC RX7 unit that is a little bigger.

Don't.

[smoothiebun]

Its been a week, and the idle problem didn't show up, but it suddenly did it today. I jumped ten and gnd and she stayed at that high idle, I then turnwd it off and turned it back on and she still stayed at high idle. Its the iscv, I ordered the new gasket so I can go ahead and fix her.