with idle being rock solid????

 

not sure, but my cpv line was ran to my vaccum line off my procharger, it came off...i couldnt find out where it was ran so i put a catch can on it..my idle seems normal..i would think there is an opening on my vaccum line now

 

I'd like to know this too and not have to resort to using a vac guage.

 

What's the problem? Why do you suspect a leak.

 

I have a cosworth plenum, lol.

 

other people are, im not at all. I am convinced that i don't have a leak because i am not seeing any decline in power or anything like that. I just want to know if its possible to have a leak and have the idle be steady at all times.

 

bump/

 

Yes, it is possible to have a vacuum leak and still have a steady idle. The way this happens is there is a bad seal that is fine under idle vacuum (18-20 hg), but under part-throttle, a leak is caused by by the rising vacuum (22-26 hg). At full throttle, there is no vacuum made therefore there would be no vacuum leak. Basically what you'd get is a car with a normal idle and normal WOT performance, but really crappy normal driveability. The acceleration could be really choppy and a CEL would most likely be thrown (probably a MAF CEL).

It is also possible to have crappy WOT performance if the leak is occuring around the intake tube or anything past the MAF that has stress on it when the engine rocks in it's mounts.

 

What is the best way to check for vacuum leak under part-throttle besides vac guage?

 

it could be an exhaust leak as well either at the exhaust manifold or after the cats

 

IF it's a vacuum leak at the manifold, it would still be leaking at idle. Idle represents the high vacuum pressure. You could try spraying WD40 around the seal and see if the idle changes. ie.. goes up = leak. Nothing = no leak.

 

thanks! I'll try that. Honestly, I don't believe I have a vacuum leak with the Cos plenum, everything is running fine, I may just do this for peace of mind.

 

Whoever told me this was suspecting a manifold leak. Thanks for the responses. I will try that wd40 trick see what happens.

Jeff how accurate is this method?

 

Is using some soap and water around the seals and looking for bubbles another method?

 

I dunno. It's just a hick/cheap method to try. FI guys will spray soapy water onto their connections to see if they have boost leaks. But don't do this on a NA engine! lol.