Started the car this morning, and the idle shot up to about 1700, and then started settling down but running rougher/stumbling as the rpms came down eventually to stall when it reached about 800, so restarted but had to apply a little pedal to keep it running, then on rolling up to 1500 and 2000 in park i checked all my gauges fp fine and moving, oil pres good, af really rich but i figure its trying to keep the car running, then i get to the boost gauge and when i'm close to idle its between 0 and -5 , normally its about -17 vacuum , so low vacuum near idle is saying to me vacuum leak right? Then it gets weird, as i accelerate in park it shows increasing vaccum all the way to -18, but when i put it in drive and brake torque it a little i hear the turbo spool, but my gauge stays at the 0 line. So at this point I know my turbo isn't seized, but i'm a little confused as to what would make the vacuum increase like that. Any thoughts?
Negative vacuum in park while rev'n engine.
- Thread starter youngstr
- Start date
Welcome!
By registering with us, you'll be able to discuss, share and private message with other members of our community.
novaderrik
Well-Known Member
- Joined
- May 12, 2004
- Messages
- 8,076
you have no vacuum at idle because you are holding the throttle blades open to keep it running, then when it revs a bit you get vacuum because of the engine speed.
you have a vacuum leak somewhere. check all your hoses for any that either aren't connected or split somewhere. could also be the IAC valve hanging open for some reason, too.
you have a vacuum leak somewhere. check all your hoses for any that either aren't connected or split somewhere. could also be the IAC valve hanging open for some reason, too.
The iac seams to be allowing the ecm to control the idle, but it is surging cause it gets near idle and stumbles, like when someone puts their foot on ur tail pipe, I will check the IAC #'s in a little while before i go to sleep, work 3rd shift.
Last edited:
I checked all my vacuums, they're ok no cracks, the idle goes up high on start up, then comes down to almost idle then shoots back up again. i'll have to plug in my laptop to see the iac counts since powerlogger took them off of scanmaster, gotta read them right out of powerlogger. My vacuum goes hard to the negative side when my idle goes up, almost like when ur Cat crumbles and clogs the exhaust.....think i should go hit it a few times with the ol rubber mallet to see if it sounds like sand in there?
crashedout1
Active Member
- Joined
- Feb 23, 2011
- Messages
- 439
Corvette?
- Joined
- May 28, 2001
- Messages
- 16,558
It appears as that's what he said.............
I wanted to put a log in for u guys, but i can't upload the file and don't have a server to park it on. Its an ugly log, iac is bouncin between 50 and 110, but there might be an ecm issue too..... got codes 55 44 42 31 24 13 its a digital dash car, so i'm gonna swap the ecm with known good , and i ordered an iac motor/valve. we'll see where that gets me. It runs into boost fine , just the idle is all screwed up.
Where is your boost gauge hooked to.? check that hose also check the vacuum block on top of your throttle body while the car is running spray starter fluid around and on those hose and PVC valve and the hose going to the fpr see what you come up with I know you said you checked your hose but sometimes when in a rush we tend to over look things take your time .
- Joined
- May 28, 2001
- Messages
- 16,558
..
Boost gauge is mechanical, and is hooked in as per the 85 vacuum set up, got the diagram had to buy the y splitter and use the orafice and had to make sure it was on the proper side of the y splitter, the vacuum lines are pretty unruly looking but that set up has worked well for about 3 years now. I'll hold it and put it to boost and have my friend spray some soapy water on the vac block, that will work as long as i have it at 1 or 2 lbs, (don't have starter fluid handy, car's rarely given me a problem starting , except when a bat dies or a fuel pump dies. I get what ur saying with the starter fluid, if u spray it and the idle kicks up then u got a leak right?
I work 3rd shift , had our christmas party last night so, i'm not that motivated this morning, i'll get after it this weekend, besides i wanted to swap ecms anyway its been doing squirlly stuff for months now, if it don't clear anything up code wise then i can just put the other one back in, seeing all those codes has me a bit concerned, one was for spark control, another was no power to wastegate solenoid and i think one was for the speed sensor? seems odd to think that all that stuff could go wrong at the same time, so maybe an ecm swap will give a better picture.
With that many codes you should just scrap it.
I’m sure there is one code that’s gone bad that is causing the others to go haywire.
I’ve seen it before.
How is the MAF? I’ve seen them wreak havoc and make you think it’s other things wrong.
If you keep replacing every part you think is the cause it’ll cost you a small fortune by the time you find the problem.
Recheck vac leaks. TWICE!
D
I’m sure there is one code that’s gone bad that is causing the others to go haywire.
I’ve seen it before.
How is the MAF? I’ve seen them wreak havoc and make you think it’s other things wrong.
If you keep replacing every part you think is the cause it’ll cost you a small fortune by the time you find the problem.
Recheck vac leaks. TWICE!
D
