Philly Miata

iTrader: (1)

I started having this issue a few weeks ago but it's gotten more frequent. Upon first startup, everything is fine, but I've noticed it happen most often after I've had to drive somewhere and turn the engine off. When I get back to my car, it will start idling high, like 1700. Only when in neutral or with the clutch in. When I go into first, it lowers slightly and then goes through the numbers like normal. It has happened a few times where idle is normal for a bit, then will randomly go up when I pull up to a stop light or something. I once sat with the car idling high trying to figure out the problem, and after ten minutes or so, it suddenly went back to normal. No other issues with idle, acceleration is fine, car runs fine, this only happens in neutral or with clutch applied and only when the car has been warmed up. Today, after about a 45 minute lunch, I started and idle was lower than 1700, but slowly creeped up to 1700 over the course of a minute or so.

wannafbody

iTrader: (1)

Maybe the Idle Air Control valve?

Ted75zcar

iTrader: (2)

Could be the cold start valve. Google it. You test it by pulling it off and putting it in hot water.

Braineack

iTrader: (62)

Doesn't sound like the Air Valve at all. It's basically a thermostat and wouldn't really open up like that. It moves forward when the clt gets warmer I can't see it gradually closing and causing the idle to move up like that. I dunno I could be wrong.

its sounds more like a simple vacuum leak, or the actual idle valve not working properly.


when you say it's fine in the gears, do you mean you have your foot on the clutch pedal, and change gears? That should have no effect whatsoever.

Ted75zcar

iTrader: (2)

I totally agree with you. VAC leak and IAC are most likely, the implication of a long time constant in the last line is curiously thermal though.

Philly Miata

iTrader: (1)

It goes to 1700 when I have my foot off the gas and depressing the clutch pedal. It also goes to that when I shift into neutral. When I shift into gear, it bogs the engine (not sure if correct terminology, rpms go down as normal when in gear prior to giving throttle) before increasing RPM with load. So basically any time the engine is supposed to return to an idling state.

Philly Miata

iTrader: (1)

I agree, it sounds very thermal, I'm absolutely sure it has something to do with something being warmed up and affecting the idle. It's normal when I first start up on a cold engine. Strangely this hasn't happened EVERY time I've run the car warm recently, but nearly every time I run the engine warm, it will go to the inappropriate idle.

Braineack

iTrader: (62)

...

let's say you've come to a stop.

gear selector is in 2nd and your foot is depressing the clutch. your idle is at 1700, correct?

now you move the gear selector to neutral and left off the clutch pedal. your idle is still at 1700, correct?

When you shift into gear, your engine bogs because youre not giving the car gas and dunno how to drive a manual gearbox, correct?

Philly Miata

iTrader: (1)

No I don't mean that it bogs and stutters, I know how to drive a manual gearbox, I mean that my RPMs go down like the engine wants to return to a normal idle RPM right as I'm going into first or second while accelerating. But yes your earlier questions are correct. Gear selector can be in any gear but clutch depressed it's idling at 1700. Gear selector in neutral, foot off clutch, it idles at 1700.

Braineack

iTrader: (62)

sounds like you have a vacuum leak. are you missing the cap on the rear of the IM?

Philly Miata

iTrader: (1)

I'll check for a missing cap and look up any other ways to check for vacuum leak. Thanks for the input Braineack-ack-ack-ack-ack

Braineack

iTrader: (62)

You oughta know by now

fig

Philly Miata

iTrader: (1)

I'll try this, fig. Thank you.