Recentlyconverted

Hey Guys, I'm having a weird problem with my car, and was wondering if anyone might have any ideas on this. Ever since I've had my car I have had a steady 18mmHg vacuum at idle when the car is warmed up, but for the last few months I've noticed that when the car is warm my boost gauge is reading about 16mmHg when at idle, the weir part is when I turn the fans on in the car by turning the ac on, the idle on the car will go from like 750 to 1000 rpm like normal, but the vacuum will go to 19mmHg like I always used to before. The car runs fine and have not been noticing any coolant loss. I also notice that when I press the brakes there is a very slight blip in the rpm, like it will go from like 750 to like 700 rpm. Not really sure what the problem is here. Anyone have any guesses??

1QWIK7

iTrader: (33)

Wow, i really want to know too because i been having the SAME EXACT problem.

However ever since i changed my gauges to DEFI, my vaccum readings seem (better?), on cold startups, it shows 18inches as opposed to my previous gauge autometer which read like 18in also but when warmed up, goes to 16in unless i manually turn on my fans which then raise the idle to 1k RPM with a 18in vacuum.

dgeesaman

iTrader: (7)

Vacuum changes with RPM (assuming no load), so could it be as simple as a change in your idle?

If that seems possible, I'd start with the simple stuff - TB sensor adjustment and IACV cleaning.

Dave

Recentlyconverted

wow, interesting, cause I currently have the autometer gauges, because of the electrict load when putting the fans on, I definately think it is electrical in nature, not sure though. seems weird. makes me wonder if my boost readings are right.

Recentlyconverted

yeah, I guess it might be the tb sensor, 750 idle does seem a bit low, but the car has always ideled at about 750, so not sure if they are connected. IAVC, is that "intake air valve control" (i.e. air intake)??

Recentlyconverted

yeah, I guess it might be the tb sensor, 750 idle does seem a bit low, but the car has always ideled at about 750, so not sure if they are connected. IAVC, is that "intake air valve control" (i.e. air intake)??

dgeesaman

iTrader: (7)

Er, IACV is the Idle Air Control Valve. It's under the UIM very close to the TPS - and is one of the components that controls/affects idle.

Actually, now that I think about the proper starting point is to adjust the idle itself first. Then try the IACV cleaning and TPS adjustment if that doesn't smooth it out.

IMO, this is all a pretty harmless thing. Unless your idle bounces around or you're getting weird response on very light/low throttle, you could leave it alone.

If your gauge goes back to zero when the car isn't running, it's probably quite close. If it doesn't go back to zero, that amount tends to be the amount it is always off by (e.g. if it zeros at 1, then 10psi is at 11psi on the gauge, and 16inHg is at 14inHg on the gauge).

Dave

1QWIK7

iTrader: (33)

^Good point

On a side note, can a difference in make of gauges vary in giving vacuum readings?

Cause when i had my autometer, seems like i wouldnt get good readings sometimes (or so i think) but after i switched to defi, seems like the readings are correct now, 0 when car off, boosts right etc.

sevensix

iTrader: (1)

what is typical vacuum at idle...

hard to believe its in mmhg... 18mmhg? doesn't seem that amount can be accurately read on a gauge.

seeing as they go typically have a range of 760mmhg vacuum to 2.0bar or psi gauges i see from 30psi vacuum to 30psi boost...