dzungh

Hey guys,

When I first got my car in November, my boost guage was reading 18 vacuum at idle and now it reads 16 at idle. Should I bank on doing a rebuild soon?

Thanks
Zoom

Swamp RX-7

No, the vacuum can vary depending on many things. For instance, your throttle body gasket my need to be replaced, or even the lower intake manifold gasket. The only sure-fire way to check engine health is a compression check. However, my vacuume varies a lot, sometimes it's 20'', and sometimes it's 17'', just depends. Hope this helps.

dzungh

Now that I think about it, sometimes when I put the car in neutral and roll to a stoplight, my engine will still be revving at 1200 rpm until I tap the throttle. Think the throttle body is sticking?

Swamp RX-7

It could be the throttle body, but it could also be a sticky dashpot.

Street King

Yup a sticky dashpot will make it idle like that.

93TTRX7

i have the same crap, what's a dashpot?

Street King

Dashpot is what slows down your rpm's when you let off your gas. It starts to slow them around 1200rpm's till its settled at your idle rpm. Vice versa if the valve wont go in it will keep it idleing at 1200 rpm's till it goes down. Go out rev your car and if it either goes down to 450 rpm like its about to shut off then back to normal idle around 700rpm or if it sticks around 1200 rpms the rod isnt being depressed, it's probably your dashpot. Not an uncommon problem.

jspecracer7

anyone got a pic?

Street King

Why would you need a pic? I thought you were VERY familiar with the workings of a FD. Not being rude, I just thought you knew your FD's.

Liemoanh

How would this effect readings. My readings where at 19 when it sat at 750 rpms. Now at 750 rpms the vaccum sits at 16-15 hg. My recent compression test shows 100 psi on both rotors, so I'm assuming its still good. When I turn on the AC the vaccum drops to 14-13 and when I turn off the AC the vaccum stays at 14-13 and never goes back to 16-15 but if I tap the throttle and the vaccum sets at 16????? I alos have the 1200 rpm thing happening to me but if I turn on the AC and then off real quick it drops below to 900 rpms and sits at that. Any advice.

94touring

I had no clue what a dashpot was up untill about 3 weeks ago, and i'm pretty familiar with the fd. Anyhow, its the screw with nut that can be adjusted that manually adjusts the throttle cable position.

Swamp RX-7

More than likely it's your throttle body gasket. The original throttle body gasket on our cars were paper, so after time the paper breaks down and will no loger be able to hold a seal between the extention manifold and the throttle body. The new gaskets are metal and work a lot better. The symtoms of a bad throttle body, and lower intake manifold gasket are : Low vacuume, and high idle.

93TTRX7

hmm good point...would oil spots under the upper intake manifold/throttle body connection be another sign? I'm guessing the oil might be leaking through the gasket and onto the crap beneath it

LetsGO7

iTrader: (2)

yo dudes...

my vaccum reading at idle varys from .60kpa(x1000)~.56kpa(x1000) and this is from Profec B spec II...any take on this?

Also my air pump doesn't work. (DAMN IT!)

-joe

LetsGO7

iTrader: (2)

bump

clayne

Yep, mine does this too.

Let off throttle, drops to 800, then pops up to 1200 rpm for about 5 seconds then settles to 800 rpm again.

I *did* pull my TB without replacing the paper gasket and I wouldn't be surprised if it needs replacement.

I see 450-460 mm/Hg at idle.