Vacuum help

[mk3-4-me]

so i just got my car running after a rebuild and im still working on getting it ready to drive.

My car right now idles real rough at around 1k for a little bit. When its idling at 1k my boost guage stays around 3 psi of vacuum.

After idling there for a little bit, it starts to rev its self up to around 2.5k with the vacuum going down to around 7 or so.

when i hit the gas it goes up to 3.5 k and drops down with the boost getting to 3 psi.

what do you guys think?

 

[bozosoku]

Vacuum leak ? Idle should be 650 rpm with minimum 7 psi vacuum according to TSRM, my vaccum at idle is 18 psi.

 

[hvyman]

normal is around 17-20. Check for vac leaks. Everywhere.

 

[CyFi6]

Are you using an actual vacuum gauge (not the dash gauge) and are you sure its plumbed into manifold vacuum and not ported vacuum? (make sure its not using a throttle body port to measure vacuum, make sure its coming directly off the manifold)

 

[mk3-4-me]

Ya its aftermarket and i have it connected to the 2 vacuum ports for the egr line on the top of the throttle body... So where do you think i should put it?

 

[jetjock]

"make sure its coming directly off the manifold"

 

[RazoE]

use the stock location on the back of the manifold..

 

[Inygknok]

use the stock location on the back of the manifold..

x2. I had the same issue the other day until I remembered the nipple at the very back of the manifold.

 

[mk3-4-me]

ok ill hook it up there tomorrow and try it.

 

[89supra7mgte]

Just for reference, vacuum is inhg, not psi. got a little confused looking at that. I would check all ic pipes. as well as relocating gauge to back of manifold. or tapping into the boost psi line, which comes right from manifold

 

[mkIIIman089]

Why does everyone seem to think vacuum leaks occur in pre-throttle charge pipes?

 

[mk3-4-me]

so i put hooked the guage up to the back of the manifold like you guys said, and its still the same... I get about 7 inHG of vacuum.. but wen the engine revs its self up to 2.5 k and back down (keeps doin it over and over) the vacuum goes down to about 15 or so.

shouldnt the vacuum get closer to boost when the egine rev up higher?

i mean when i hit the gas it revs up to 3.5 and stops, but the vacuum goes up to about 3 psi of boost.

I just redid IC piping, checked for bad vacuum lines and that didnt help. It idles really rough barely staying alive. I timed it and got it to 10* btdc.

My oil presuure guage also reads about 43 psi when it idles... I read somewhere that it should be 4.3 psi.. what do your guys oil presuure guages read at idle?

 

[CyFi6]

Do you have any codes? Even if the check engine light is off, you can have stored codes. Hook up your jumper and check. Your vacuum should be anywhere between 18-22inhg approximately at idle, but that is assuming you have a steady idle. Is it smoking or anything unusual out the exhaust? You aren't going to make boost just revving the engine up, there has to be a significant load on the motor to make boost(driving). Oil pressure will be higher when it is cold, 4.3 is the minimum spec for a fully warmed up engine at ~650 rpm.

 

[mk3-4-me]

havnt checked for codes... im going to today hopefully. It just what it says on here right? http://www.cygnusx1.net/Supra/TechTips/engine_error_codes.aspx

I thought the vacuum was off, and was wondering how it made boost without load... lol

No no smoke, i mean a couple tmes there was some white smoke on start up, but thats just cause it was cold i think, it goes away. i just put a new HG so it isnt that. lol

 

[mnracer550]

with that reving to 2.5k it sounds like the tps sensor. mine did that when i forgot to plug it it in once. get some carb cleaner and start spraying down vaccum lines and ic piping and anywhere u could have a vacuum leak to try and find it. when u heard the engine rev a little that where the leak is.

---------- Post added at 10:51 AM ---------- Previous post was at 10:50 AM ----------

oh, and mine usually sits about 20 psi at idle and around 40psi wot at operating temp

 

[mk3-4-me]

ok so i got the codes:

24 - intake air temp sensor -- what is that?
31 - AFM signal -- need replacing if that codes comes up??
41 - TPS -- replace?
51 - Idk why i have a knock sensor code cause they are both in. Do those go bad?

what do you guys think? replace everything? id rather not if i dont have to. How much is everything do you think?

 

[CyFi6]

Sounds like you have your AFM unplugged first of all, considering the intake air temp sensor is inside of the AFM and uses the same connector. Go make sure you have a good connection there. Then, go into the tsrm and find the TPS adjustment procedure and verify your TPS is good, has the proper adjustment on it, and is plugged in with a good connection. Worry about the knock sensor codes later once you get the thing to run right.

 

[mnracer550]

yes knock sensors go bad like every other sensor. ohm it out to see if its the sensor its self or the wiring to it

 

[mkIIIman089]

IIRC it's almost never the sensor... which isn't even a sensor, really.

 

[mnracer550]

i replaced one in my buddys dsm a few days ago. what would you classify it as then? a switch?