Vacuum reading question.

[sleepyalero]

Okay, most of you know my mods, ive recently encountered a small problem.

Story goes....

Every day before i drive the car i let it get to 180* before i drive it. Once warm i pull out of the garage and im on my way. If i do a WOT pull right after leaving the garage (or parked anywhere else) the rpms will hold anywhere from 1100-2400, after i do the wot pull i can sit in neutral out of gear and it just holds anywhere between those rpms. Once it does that i cant drive and have to shut the car off for a few before i can start driving again so the rpms will sit normal. BUT if i drive casual for the first say... 5-10 miles then do a WOT pull. The car wont do it, only after i first start the car up. If that makes sense?

So my question(s) are....

1. Whats the hg vac reading for a 3400?

2. Do mods like i have... Egr delete, ported uim/lim, 65mm tb etc... Change the vac reading?

Back when i used to have a vacuum gauge the car at idle sat at 15 hg. I just got one today and it now sits at roughly 18 hg.

When this happened i figure i either had a vac leak or its a tuning issue. Right now im leaning towards vac leak. Anyone know? Have ideas?

[sleepyalero]

Update: i did some searching around on the car, saw that a header bolt on the rear header was backing out. Possibly leaking... So i tightened it down and about to see if my vac is reading any different now...


Looking on google, its telling me 17-22 at idle is normal or "healthy"

At idle im reading 19.

[guiguilandry]

how's your needle reading ??? stable or jumpy... it should be stable, on my 3800 I have 22...

[sleepyalero]

Im sure its different for every motor. But like i said 17-22 is normal.

At idle rpms hold real steady.

[guiguilandry]

ok, so no intake leak... for your jumpy idle I think it's the IAC, because when you turn the car off it return automatically to a preset position....

remove it and clean it with intake cleaner clean also the inside of the TB
I had this happen on my LD9 before and it was the IAC sticking into the TB

[sleepyalero]

I just replaced the IAC about a week ago. Along with the purge valve solenoid, and the maf is brand new its a 65mm tce tb. Took the hose off the other day doing IAC and purge valve and the thing was literally spotless.

Its not a jumpy idle, it will literally hold idle at 2200 rpm ( happened avout a week ago) and it doesnt settle down unless i shut off the car for like 20 mins.

[AleroB888]

...Its not a jumpy idle, it will literally hold idle at 2200 rpm ( happened avout a week ago) and it doesnt settle down unless i shut off the car for like 20 mins.

You need to find out what the tps is reading when that happens.
For example, if it reads + 2 degrees when it should read zero (with your foot off the acc pedal) it can increase the rpm by increasing the timing.

[sleepyalero]

If i had hpt or something i would! Lol :(

[Starglow]

I just replaced the IAC about a week ago. Along with the purge valve solenoid, and the maf is brand new its a 65mm tce tb. Took the hose off the other day doing IAC and purge valve and the thing was literally spotless.

Its not a jumpy idle, it will literally hold idle at 2200 rpm ( happened avout a week ago) and it doesnt settle down unless i shut off the car for like 20 mins.

You might need to calibrate that new IAC valve so the PCM knows it's position. I forget the exact procedure, but it's turn the key on for 10 seconds and then off or something like that. I also agree that you should check the TPS as well which sits right below the IAC.

[sleepyalero]

I will look into the tps...

Thing is with old iac it did same thing, you think it would need that? I figure you unplug battery for 10 min the pcm would relearn everything?

[AleroB888]

I use an old "Auto-Xray" handheld scanner for most routine cruising, because the car is so heavily modded. I have not priced them lately, though.

Does Autozone rent those out? lol

[sleepyalero]

Im not sure, ill look into that in a few. Will it tell me like everything like hpt?

[AleroB888]

Im not sure, ill look into that in a few. Will it tell me like everything like hpt?

It tells you most things but not all are displayed at the same time. There is a way you can record a whole scan, but I never used it for recording since I have HPT.
I only use it as a convenient way to spot check the car, since it doesn't take up much space.

[sleepyalero]

Yeah ill check it out. It would be nice to have hpt tho.

May run out to MMS and have him scan it. Only costs me about 40$ to get there/back.

[MMGT1]

Key on, unplug TPS and IAC. Key off, key on, twice. Then off and reattach connectors. Try it
If you pull the PCM IGN and PCM BAT fuses under hood then key on. Wait about 30 seconds and you should hear three chimes from inside the car. Key off and reinstall. Will clear everything stored and forces learn mode. It's like hitting the "fuel trims reset" using HP Tuners

[MMGT1]

Oh, your vac hg is fine man. As long as your over 15 your good. When you get into really big cams and you drop below 15 is when you need a vac canister because brakes will not operate properly below 15hg

[sleepyalero]

My car doesnt make chimes so i guess i could count to 60 to be sure?

Thanks for the input paul really appreciate it.


Ill have to try this tomorrow.

[a.graham52]

sleepy, dont you have an ultra gauge?

[sleepyalero]

Nope :(

[sleepyalero]

Okay paul, tried that, didnt really help. But thanks for the advice. My next step is new tps.

Asked a buddy of mine who knows alot about cars ( more then me) he said it could be a number of things and cant really suggest anything until i had a tuner hooked up to see whats happening.

Few others i told my issue, they are pretty dead set on me getting a new tps, along with fisdad.

[xXManwhoreXx]

The luls if throttle cable getting stuck

[sleepyalero]

Its not.

[falloutboy]

to be honest, before u buy a new TPS sensor, u might wanna do a "Rauschprüfung".
Sorry don't know the english term, basically what u do is check the resistors in the sensor and see if they read intermittently or have "hiccups".

A new TPS or IAC wont do u good, if u can't relearn ur computers properly. And even if the ones in there right now are off, they most of the time can be readjusted.
But I assume only a TECHII can do this, as u not only read data, u write data.

[sleepyalero]

Thanks, so kinda like hpt for tunes?

[[ion] C2]

Its not.
my plate used to stick, had to slam it closed a few times to get it to idle normal and not try to drive away

TPS/IACV, vacuum leak (which may or may not show up on your vac readings as you expect it to, do not listen to anyone's "if you're in this range you're good" advice. it varies.)

[sleepyalero]

Ive slammed it shut when i had high idle, still does it, i believe it has nothing to do with the trottle plate.

Vac leak could still be possible. But i dont think very likely atm. I hear no hissing under the hood indicating one, or with the gauge.

The tps is still a big question to me. Its been awhile since ive got one, and it was in my old TB and swapped into my 65mm tb when i got it.

One problem im also having now is where the pipe goes into the muffler is coming off. Damn flowmaster.... The whole pipe/tip on passanger side is attached by only 1-1.5 inches of metal till it falls off. Plan on getting that welded back on soon.

[sleepyalero]

Got a new TPS today little hot out so i will wait till the sun goes down to do it, been doing yard work all day tired of the heat lol will report results later

[sleepyalero]

Tps did not help my situation :(

[AleroB888]

Tps did not help my situation :(

Then you should put the old one back in and save the new one.

I was going to ask, what if you start the car cold, but instead of warming up to only 180 degrees, let it get to full operating temp or about 200 degrees? Does it still act up?

[sleepyalero]

Car doesnt go to 200, fans are set to keep it below that, unless its a hot day.

[[ion] C2]

Ive slammed it shut when i had high idle, still does it, i believe it has nothing to do with the trottle plate.
I'm sure you manually operated the plate as well, just to make sure, right? I used to be able to close mine by hand when it would stick.
Vac leak could still be possible. But i dont think very likely atm. I hear no hissing under the hood indicating one, or with the gauge.
Neither did I when my manifold was cracked.

I dunno.

[sleepyalero]

Yes ion. And nothing is cracked from what i can see.