Very Weird Idling... Situation.

[blk92z34getrag]

This isn't the one all the LQ1 n00bs post about.

When I shift out of gear after accelerating the car won't rev down immediately, it will stay at whatever RPM, or go up slightly, for a second before revving down. And sometimes when I shift into neutral (i.e. when slowing to a stop light) is will idle REAL loud, and idle at like 1000RPM. When it does this, the engine makes a sort of hissing noise... I can't really explain it. It's like crossing the engine noise and a person going SHHHH. That comes from the engine, and from the exhaust it is REAL loud. Like at if the engine were under load in 5th gear going 30MPH doing 1000RPM, that kind of loud. The remedy this I have to stab the pedal a few times. And if I don't, if I accelerate from the stop it will bog, and occasionally stall.

What would cause this odd behaviour? I haven't replaced anything because knowing this engine it would be futile without an idea of what it could be. I thought it might be with the TPS. But I have no clue.

[Anonymous]

I really have no clue.

As for the stay-idle when you shift, most cars do that in an attempt to save trannsmissions from bad drivers who don't understand that the clutch needs to be not only used, but used often and correctly. It just aligns the gears better when you shift at rpm. I hate it. It bugs me. My car doesn't really do it at all, but my sisters Honda and my friedns 98 Z24 do it really badly.

it sounds like a vacuum leak, which would cause a hissign and a high idle that wants to stay high.

[blk92z34getrag]

But it isn't "high." Only like 1000RPM. It's just really loud. I couldn't imagine it being a vacuum leak. The uim and lim gaskets are only 1.5 years / ~12,000mi. old, and I replaced every vacuum hose I could find (Including the brake booster hose, the "oil distribution cap" hose that sits under the lim, PCV, everything).

I wouldn't rule it out. What's the easiest way to find a vacuum leak? I think I've heard spray carb cleaner on the intake, heads, hoses, etc., keeping away from electronics, and watching for bubbles, correct?

[Anonymous]

Well unfortunately on this car you can have a vacuum leak nearly anywhere. It sounds a lot like a leak. Also, 1000rpm is a bit high, and a good sized leak can still let the car idle at 1000, since the IAC will just close itslef completely. I know some guys have a had a leak from the EGR...

On your intake gaskets, spray carb cleaner around the joint, and if the car's idle starts fluctuating, than it's leaking. But I wouldn't be so sure that it is the manifold gaskets.

From what you are saying, it sounds a lot like a vacuum leak...Does the car have good power still when you step on it? Any SES codeS?

[blk92z34getrag]

Still has all the power it's ever had, and no SES code.

Though, now that I think about it, when I replaced the EGR valve I had to cut my own gasket, and I'm sure it isn't perfect. I used a lot of sealant though (high temp stuff, I learned the difference the hard way ).

Thanks for the advice.

[Anonymous]

Well with a lot of sealent, I doubt you have a leak.

Hell I am using a thin block off plate with a gasket and sealent, and it isn't leaking.

Overall, I think it is safe to say you have a leak. Now how bad it is or where it is, that is tough to say.