ok so I was out driving last night. when I got home I noticed that instead of idleing at the usual 16-17vac it was more like 14-15 vac at idle. and if I rev it up a little and just let off the gas, the rpms drop and the car stalls. (not everytime just sometimes) car still drive fine, and it idles ok, not lumpy or anything. just the loss of vac worries me. also the car dying on its own isnt good either.

oh and there is no smoke at all and it didnt overheat.

 

Make sure the air pump is working and you didn't pop the airpump fuse - with the airpump disconnected, the car will drive weird and you will lose idle vacuum. This can happen easily if the wiring to the air pump is old and some of the insulation is missing - if it touches ground, the fuse will pop. It's the AC fuse under the hood, BTW.

Dale

 

air pump has been removed

 

anyone?

 

Maybe you got a vac leak somewhere. at work, we always use brake clean and spray down all the hoses and stuff. when the idle raises up, that's where the leak is. worth a shot.

 

so the idle will raise when the brake cleaner gets sucked in?

 

I prefer to use starting fluid instead of carb cleaner. It evaporates quickly and doesn't leave a residue behind, and yes the car will rev up/smooth out if it sucks that stuff in.

It's most likely something simple. What ECU are you running?

Dale

 

stock ecu with split second additional injector controller.

here are mods fyi.
greddy 2row fmic
koyo rad
hks intakes
m2 down pipe
megan racing midpipe
racing beat single cat back
split second additional inj controller w/ 2 extra 750cc injectors. (increase fuel as boost increases runs a constant 10.5-11.2 afr under load)
run 10 psi around town-13psi when racing. (spikes 14)



also, spraying that stuff on a hot motor wont catch fire?

 

You obviously try to keep it away from the turbos/exhaust. To see how your motor reacts to ingesting starter fluid, let it run and spray a small shot right into the air filter/intake, and wait about 3 seconds. Now...whatever it just did, it will do again if it ingests more fluid later via a leak.

So are you gonna tell us about the high rpm boosted runs you were making, or not?

 

they are in the kills section the one about the evo and the z06

 

If your vacuum truly has dropped and there is no leak, you may want to drive the motor easy for another few hundred miles again. What happens when you lose vacuum/compression after hard runs is that the seals have warped a little. Sometimes due to high AFRs/EGTs, sometimes due to lack of premix/oil injection. It's impossible to know for sure, but it isn't an assembly error or a seal defect most times, but something with your tune. Driving easy again (like another breakin) will allow them to wear back flat again and restore vacuum/compression in all but the most serious cases. OF course, you need to fix whatever the cause was before you lay into boost again.

 

well I hope that is not the case. my afr's were always below 11.2-11.3 mostly in the 10's.

sometimes it idles at the correct vac (around 16-18) and sometimes it goes as low as around 14. the idle is not lumpy or anything like that, its just the vac is off a little bit and the car sometimes dies when i get off the gas and push in the clutch.

also a friend of mine told me a quick way to check comp was to get up to like 20 mph and put it in 4th and go wot. if it is smoth then its ok, but if its all jerky then there is a problem. I tried that and everything seems fine.

 

How a car responds in 4th gear has nothing to do with compression.

 

Have you done anything to check the vacuum yet?

 

im stuck at work untill 5pm. after that i am taking a trip to the parts store to get some starter fluid and start spraying to check for vac leaks. i try to get as much info as I can before I start trying stuff I dont know about.

 

I would do what Kevin recommends first. If the car is driving fine aside from the change in vacuum, I would drive it easy for a few hundred miles and see if the vacuum builds back again.

If the car is not catching the idle when you rev it a little, you might check the Dashpot.

 

Strangely I have the same problem but with no stalling problem. My motor is pretty new but past the break-in period. I did a few hard pulls in second gear and then my vacuum was shot at about 14. No other symptoms like lumpy idle, which normally indicates a chipped seal. Now I have been driving easy and the vacuum keeps doing different things every time I look at it.

I can't imagine warped seals from EGTs however my oil pressure has been bouncing around a lot. I have been thinking it is the sender unit because it jumps down and back up so fast you can literally hear the needle hit the peg at zero psi. I'm guessing and hoping that my oil pressure isn't actually doing this.

My guess is a failing solenoid. I'm wary of this idea of spraying starter fluid in that area. I have seen it done to test gaskets but there are many areas that could cause low vacuum. Intermittent vacuum would seem to point to something other than an engine seal or gasket.

 

Check the LIM gasket - mine did something similar for about a year and ultimately failed. If it is original it is paper and leaks then no problem for a bit and leaks etc. You should consider getting the car smoked for the vacuum leak as spraying stuff is not exactly the most reliable DIY.

 

ok, well I went home and along the way home, I got a check engine light anyone know how to "scan" these cars? I know they are not obd system. sprayed the starter fluid, and came up with nothing. Im almost tempted to bring it up to pettit, but really dont have the money to go through all the maybe this maybe that bull ****. So frustrated.

 

http://www.fd3s.net/engine_codes.html

 

thanks.