Does anyone know what the vacuum should be set at? Mine is at 21in/lbs at idle. Does that sounds right nor not?

Thanks
Chad

 

Yes. that is right about normal. 20 inches give or take an inch or two is fine

 

Thanks man

Chad

 

That would be 21 inches of mercury, or 21"Hg..... not "in/lbs"

And that is fairly normal for a stock cam.

 

Oh ok thanks Injuneer.
If my vacuum is pulling a near normal 21 inches of mercury, is it possible that I'm still having a vacuum leak?

My car is idling about 1800. When i unplug my IAT sensor the idle jumps to about 2000rpms. Then when I plug it back in the idle drops to about 1100 and it is stumbling. It sounds like I have a cam....But I don't. Then all of a sudden it jumps back to about 1600....I think that is due to the computer thinking it is running rough.

Do you think i have a leak?

Chad

 

If its idling at 1,800rpm, you have a source of air that the PCM can't control. Measuring vacuum at that rpm is almost meaningless.... you can't compare that to a vacuum value for "normal" idle.

Do you have access to a scanner? Can you check the TPS volts and the IAC counts? Are you using the stcok throttle body? Have you verified the blades are fully closed, against the stop screw? Have you adjusted the stop screw?

 

Injuneer
I am using a stock TB. On my last post, they told me to set the idle by backing off the set screw. I did that then the "tab" wouldnt go back to the set screw. There for I beleive the blades are all the way closed. And it didn't help my idle at all. I might have access to a scanner at our shop. We also have a Vac-u-tec machine that pumps smoke through the vacuum system to help find leaks but I have not had time to go and use it. But I do not know of a way to check the TPS volts and or the IAC counts. Where could the source of air that the PCM can't control be comming from?

Thanks Chad

 

air can be coming in anywhere AFTER the MAF. this unmettered air will not be read by the MAF and therefore fuel trim will not adust for it.


YOu can test the TPS with a multi meter if you have one.


why were you told to adust the idle screw? just cause it was idleing high? when did it start. anything you have done to teh car or did it just start with no real reson?

 

HBHRacing
My engine is the 1993 Model so I have the Speed Denisity. I guess I should have told you that before. I do have a multi meter so I will go and try to get a reading off of it.

I had to pull my heads due to a partially spark plug hole. Now that I've got it back together it is idleing high. Yes, they said to just set the stop screw back to make my car idle down. It didnt help. I really couldn't tell you if my car ran good before I took the heads off since I was just finishing up the V6 to LT1 swap. And this was my first time running the car.

Thanks Chad

 

Ahh. thanls for letting me know. You can can test the TPS by setting the multimeter to volts. There are 3 wires. a hot feed. a ground and a PCM imput. with one lead on ground test the PCM imput wire with the other prob. with Key on engine off throttle closed you should have just over a half a volt to 3/4 volt range or vary close.. now while monitoring the voltage slowly open the throttle. watch for increesing voltage that is smooth and no glitchs. follow it all the way to WOT and shold be over 4 volts.


I would also take a look at your MAP sensor.. you can test it the same way. at an idle you should have around 1.5 volts. now with RPM the volts will incress but will head back twords 1.5 when the RPS stableie. if the reading is very high you might have a vac leak

 

HBHRacing
I just got done checking my TPS sensor. With the key on I got a reading of just a tad over 1/2 volt. So that is good. But when I opened the throttle it never moved at all!!! Does that mean I have a bad TPS? If so would that cause the 1800rpm idle?

Do you check the MAP sensor the same way. Key on but engine off? Because I started the engine and un plugged the MAP sensor and the engine died.


Thanks man
Chad

 

hmm. well. for the TPS I woue remove it and see if the blade that sticks out is contacting the grove in the TPS. Remove it and leave the connector attached. run the sweep test again by moving the arm in the TPS by hand. if it still doens't move then replace it. it would assume that you have adiquite ground and voltage to the sensor considering that you had a normal output signal. "USUALY" when you have around .5volts it should have a stable idle however if it's still tests bad get a new one.


as for the MAP it should be tested with the engine running. howeever if you have a hand held vac pump you can test the acual sensor itself but this will not help you with how the motor is running. if you do have a pump with the key on engine of (KOEO) you should have 5 volts with no vac aplyed. the more vac you appy the lower the volts. if it tests clean and smooth then the sensor is good lemme see if I can find a voltage to Vac chart...

but. to see how the motor is running its best to scann it with teh car running cause it will tell you by voltage how much vac is coming to the sensor.

also. you can try with the engine running unplugging the IAC and see if it stabizeds the idle. without being able to see the IAC counts/steps it is hard to tell you if it is stuck but if the TPS don;t fix the problem I woud try a new one or at the least pull it off and see what it looks like

 

HBHRacing
Thanks again

I'm going to pull off my TPS tomorrow. I'm just wondering if I tested it right? I unpluged it and then put the ground probe on the ground on the plug. Then put the Red probe on the PCM part of the plug. I'm starting to think that I did it wrong. But how would you test it with the plug plugged in? Also if my TPS was bad...would that bring be back down to the correct idle?

The MAP sensor I'm confused on how to check. I started my engine and when I unpluged the MAP sensor the engine died. Again I'm probably doing something wrong, but I do not know what. If you could explain more on how to check the MAP and TPS sensors I would REALLY appreciate it.

I think tomorrow I'm going to try and have my car scanned by a Snap-On scanner.

My idle is steady at approx 1800rpms. So what do you mean by with the engine running unplugging the IAC and see if it stabizeds the idle. To me the idle is steady at 1800.

Thanks
Chad

 

I've got the data for MAP vs volts, TPS, etc. in my online Scanner writeup.

You will also find guides to checking a lot of the sensors on Shoebox's tech pages.

I still think you are getting air into the intake manifold that is not passing through the TB. But first, check the actual blade postion - don't just look at the stop tab and assume the blades are closed. Make sure they are closed. You may have the cable adjusted wrong.

Then look at things like intake manifold-to-head gaskets, the TB-to-intake manifold gasket, the gasket between the TB and the bottom plate that houses IAC and coolant, EGR gasket, connections for things like power brakes, PCV valve, EEC purge, EGR solenoid vacuum, heat/air vacuum supply, fuel pressure regulator vacuum. Then start looking at the possibility of incorrectly adjusted valves, leaking valve seals.......

 

sorry. I should be more specific. what you need to do is backprobe the wires by peircing them with the prob of the Dgital volt meter (DVM) with the connector still pulged in to the sensor. when you are looking for positive voltage you use the red lead to test the hot wire while holding the black lead on any ground (usualy the negitive battery termanal)

conversly if you ever want to look for ground you want to again have the DVM set to teh volts scale and use the black lead on the ground wire and hold the red lead on a postive feed (usualy the postive battery termanal)


be using this method retest the TPS and the MAP sensor.


what I mean by with it running unplug the IAC connector..... if the PCM is sending teh wrong signal to the IAC or there is a short and the IAC has opened to much thereby increesing the Idle, when you unplug it the IAC should retract and lower the idle back to normal unless the valve is phisicly stuck or carboned up.. or it's not teh problem.


I have a ton of time using a snap-on MT2500 scanner as well as there newest scanner/scope the M.O.D.I.S.

either way... in the data they will be able to see the TPS voltage and can sweep test ii.

they can see the MAP voltage as well

also can seethe IAC counts ( if it;s way above 40 then that is most likely teh problem.

they will also be able to see most other control systems and should be able to find the problem as well as see any codes that could help in the diagnostic process.

be sure to let me know what you find and if I can help at all