I have a big problem. Anyone who can help let me know. When i step on the brakes my engine stalls when coming to a stop. What could be causing this? Any ideas? Seems to be worse when the engine is hott. This is on a 2.8 Firebird 5 spd.

 

problem in the power brake booster. you have to cheak the hose that goes to it, the check valve, and finally the booster itself. most likly the check valve though.

 

also a bad internal diaphram will cause it.

More then likely the booster itself is bad.

 

Funny how these problems show up in groups.

Its the brake booster, its either bad or leaking vacuum in its line.

Either way it causing it.

 

Don't just check the brake booster, check the whole damn vac system for cracked hoses, broken fittings, and other sources of leakage. Don't forget to check the evap can with a vac pump before you do anything though... if it's bad, you don't want to know the rest...

The problem is you have a total lack of vacuum in the system, and when you hit the brakes, the booster removes what little vacuum is left. No vacuum=no air entering engine, and no air means no run.

Forgot to add: Been there, done that. $15 total for all vac lines being replaced at same time (no hard lines).

 

Ok. This is what i did today. I searched all my lines and they look good. However there was one line that went absolutly no where. So i undid it with the vaccume sucking in air. My brakes are great and engine doesn't stumble but it is not right. I plug the tub back in with it running and the rpm of the engine goes down and then back up. Not sure what is going on. Any ideas?

 

Well, if creating a vacuum leak is helping your problem, it's probably something along the lines of a bad IAC or a clogged PCV system, or you (or someone else, or father time) fiddled with the minimum throttle position on the throttle body, and she's not getting enough air at idle to run. Plugging the vacuum leak causing the idle to lower and then come back up suggest the IAC is operating normally, though.

For a quick check of the PCV system, pull the PCV valve out of the driver side valve cover and check to make sure it's sucking air in through the valve while idling. It shouldn't pull alot of air volume-wise, but it should have strong vacuum, and should be hissing rather madly.

 

Erm.. No vacuum = atmospheric pressure = WOT ... lots of air entering engine, or the engine isn't spinning, or lifters/pushrods/rocker arms are missing...

Vacuum leaks degrade performance in MAF and Carb'd vehicles because the air is entering the system in an unmetered fashion.. in the case of a MAF EFI engine, the MAF doesn't get to read the air entering through a vacuum leak, thus the AFR at idle is generally lean.. with a carb, air entering via a vacuum leak doesn't go through the carb venturis/jets, thus doesn't pick up the fuel to account for itself.. again, lean.


EDIT --- Post #1000 --- Tagged for Posterity.

 

Excuse me. I meant to say "less/no METERED air entering engine"

 

Just checking

 

Does this happen all the time when you press on the brakes?

Or does it just happen after the engine's warmed up, and you've gone at least 40 MPH? Does the car start right back up after it stalls, or does it take a while?

I wonder if your EGR valve is sticking open. It'll activate above 40 mph when the engine's warm and the engine's at light throttle. If it sticks open, when you come to a stop, the computer "thinks" it's deactivated it, but with the valve stuck open, the engine will stall.

Next time the car stalls (and if it won't start again), pull over somewhere safe, throw it in park, pop the hood and carefully (so you don't get burned by the hot valve) feel "underneath" the EGR valve. You'll feel a cut in the bottom of the valve- thru this cut you'll feel the diaphragm. The diaphragm should be all the way DOWN, almost even with the "cut" in the bottom of the valve. If the diaphragm is raised up at all, it's sticking, and you gotta replace the EGR.

 

Thanks guys, Yeah this happens alot when the car is warm. However it does it even when going 20 mph. I also have a 5 spd if that matters. Anyone have a vaccume diagram i could use? Thanks

 

Now, TomP, I had the same problem with my V6 (before it crapped out) and it wasn't the EGR valve because I tested that with a vac pump to be fine. Any other suggestions as to what causes this?

 

It seems to do this wheneven i come to a stop or let of the gas. I'm wondering if the brakes are just a part of the problem. The car seems to do this alot more when it is all warmed up.

 

Remove and check/clean the IAC. Since you said it happens whenever you get off of the gas, that would be the next thing to check, since the computer uses that to regulate the idle speed. Also check your TPS. Instructions are on the TGO tech articles page.

 

I did some testing today. It seems as though i have no vacuum at the egr valvue. All my vacumm lines are intact also. Any clue what could cuase this? I think this is affecting my bracks? Thanks

 

Having no vacuum at the EGR valve while the engine is idling is normal. The valve is desinged to open when the throttle is opened, since the flow of gases into the cylinders will cause the engine to bog down when it is idling. Take a vacuum reading at one of the major distribution points (probably at the smaller port on the plenum tee would be best). That will identify any major problems.

 

I have no vacuum at the egr at all. Even when giving it gas, there is none. Any ideas? Where is the tee you are talking about? Thanks

 

Correct me if I'm wrong but doesn't the EGR run off its own vacuum pump???

That little electric motor near it that runs when needed??? Its does something Can't think of what off hand but it creates vacuum for something.

 

The computer is supposed to run a little valve (electronic vacuum regulator valve or EVRV as GM calls it) in that area that regulates the vacuum supply to the egr valve. Either the sensor block (connected to it by two wires and has a four-wire connection to the ECM) has no vac reading, the valve is bad, or the lines in that area are plugged.

The vac tee is in the back of the upper plenum, near the distributor. It will have two lines running off of it, one huge one and one small one. The big one is the vac hose for the brake booster and the small one connects to the vacuum tank and cruise servo if you have one. It is easiest to take a vac reading there rather than breaking the solid lines at the TB.

 

I think i know where you are talking about. There is a vacuum line that runs into it off the intake. Then it goes to the Tee. From there, there is one that runs into another platic hose which goes into the harness. The other one that is on the leg of the Tee goes to no where. Just a hose with a screw in it. I doubt it is factory. Where could this go? Maybe that is why i have bad vacuume.

 

It is a metal fitting screwed into the BACK of the upper plenum, just foreward of the distributor. It will have two lines coming off of it, and most likely either needs to have teflon sealant or to be tightened to fix the leak there, if there is one....

 

No, there are no spots were the lines are leaking.. I'm wondering if that hose that goes to no where is suppose to go somewhere? Any ideas?

 

You don't happen to know where the Emission Hose Routing sticker is (on your hood) do you? That says a lot....

Still, you should take a vacuum reading at a major point to see if you actually DO have a leak, which I am pretty sure you do SOMEWHERE.

 

As I was leaving today I noticed something I should share with you. You wont get any vacuum at the EGR while the car sits still.

See I have a vacuum gauge hook into my EGR post and use it to help watch gas mileage. As the gauge only works while the car is moving under load. You can rev all you want but sitting still I get no vacuum at the EGR post but maybe a tad. Once driving then I get all kinds of readings. And can see how much load is going on.

I like it better than reading vacuum all the time.

 

Today it was was finally warmer out. I unpluged my vacuum to see how much vacuum i had. But i noticed this. When i make a vacuum leak, the engine rpm went up a little. So i took it for a drive like that and it was alot better. Could my IAC be gone or clogged? I knwo the IAC is suppose to like create a vacuum leak for the engine. Any ideas guys?

 

IAC=CONTROLLED air intake, not vacuum leak, which is UNcontrolled air leak.

If that is one of the problems, yes that most likely can be the root cause of the rest. However, I still think you have a loss of vacuum somewhere. Cleaning the IAC is simple, remove it and the top of the throttle body, and clean out every passage connected to the IAC and make sure there is no residual carbon left to gum up the works.

 

This is the problem now. My idle is way down to about 200 RPM. The engine is just about running. You can rev it up but seems like it doesn't want to. Then it goes down to about 200 RPM again. Are you thinking this is the AIC? I will clean it out tomorrow. Do i spray cleaner in the hole where IAC is plugged in? Can I use break fluid to clean it? Also i see that there is a gasket. Should i replace it? Thanks

 

Take the top off of the throttle body and replace both the top gasket and the IAC gasket. Don't forget you have to pull the pintle (conical air control mechanism thing) out of the IAC body so that it may be cleaned. Clean all of the passages pretty good to make sure that air can flow freely without being gunked up by carbon.

The problem is that once the ECM finds a "target" position for the IAC to maintain a certain RPM level, it uses that position unless the ECM loses power and has to change it's internal settings. So, the more the engine is run, the more carbon gets in the IAC passages, and the less airspace the carbon lets the pintle have at its preset point to maintain idle speed. Therefore, the engine is choked almost to the point of stalling....

And the other part of the problem is that the ECM gives X quantity of fuel for Y quantity of air at idle. Less Y but same X means that the engine will run like crap unless more air is introduced into the engine. Creating a vac leak introduces more air into the engine than the IAC is giving it, so it runs better on X amount of fuel.

 

This is funny , I just , I mean JUST received my sunpro vacumn pressure tester gauge from UPS , and its like 10:20 at night here .heh .....You should check out there sight ...and get one for $10.00 whiles its on sale . If you lived by me Id ride over and we would slap that puppy on there ! type in Actron by sunpro in your web search engine and its should bring up there website.

 

I can do one better. Go to the local auto parts store and buy a MityVac. That will do the vac check nicely, along with testing the EGR valve (much important), bleeding the brakes, and many other things. Only $25 including tax and warranty...

 

my car idles at around 200 with the iac pluged in also and cleaning the iac and the passages did nothing.
Unplug the iac idle too high
Plug it in=idle too low.

All this = bad iac?
BTW it CAN NOT be a tune up issue since i just did the head gasket not too long ago and replaced everything.
When i put the motor back together you could see every number on the block and heads clearly, no grease or dirt anyplace inside or outside the engine.

 

Did you try resetting the ECM? So that it will adjust itself? I plan on cleaning mine out tonight and see what happens. Thanks guys

 

yup

 

Try this.
1. Disconnect the battery for more then 30 seconds.
2.Reconnect it.
3.Push throtle 1/4 of the way down.
4. Start car and let it run for 5 seconds.
5. Turn key completly off for 10 seconds
6.Start car and don't touch anything and see what happens
I just read this on mine. Haven't tried it yet though.

 

The battery has been disconnested for a month and the problem didnt go away. I think i got the iac reset thing down by now.

I'm just gonna go ahead and buy a new iac. Might as well, I think i'll redo the FPR too since it's been taking longer and longer to start. I might as well replace the damn collapsed lifter while im at it also. That damn tick/tap is getting on my nerves.

 

I just ckecked the iac with it unscrewed and the pintel shot out of it so i know its not a bad iac.

TPS check is next.....

 

Let me know how you make out man. I cannot figer mine out and it is beginning to really tick me off. Right now my engien runs great when i creat a vacuum leak. Why is that? Then when i stop the leak it runs liek crap? Could this be my egr valve? Could this be my vacuum module? Any ideas on hwo to test these or what to do. I don't undersand!

 

EGR valve is not activated at idle unless it is stuck open. You may be able to either test the regulator valve or the EGR valve, but I doubt you'll get anything fruitful from this. Is it possible you have a restricted air intake somewhere, such as the air filter? You may also look at the MAF screen if you still have one. If you don't, you may want to look into buying a new MAF... people have been having problems with the sensors when the screens have been removed. Also, check the intermediate air box that goes in between the MAF and the intake bellows for clogs or any debris that may have gotten in there, along with the intake bellows, especially the vent pipe coming from the pass side valve cover.

The problem is you have too LITTLE air going into the engine unless you open up one of the vac lines and let some more air in.

 

The car is completly stock and has always smelled as if it was running a little to rich. I drove about a mile tonight with the leak to see what affect it had. I have way more power now and it does not smell like it is running rich. What ya think now. I still have a clog somewhere? I will check out the screen tomorrow and see if it is cloged. This could control how the engine runs? Thanks

 

When was the last time you checked the vapor can? I had that same problem till the engine DIED on me... Get the MityVac... it has instructions to tell you how to test the can for vac leaks or anything like that. Change the filter. Shake the can, and if it sounds full of gas, get a new one.

There. Problem solved possibly?

The screen in the MAF controls the airflow into the sensor, by straightening the flow out so it can be more accurately read by the sensor. Check for codes.

Here's the deal. You have either too MUCH gas, too LITTLE air, or both. Start at the air filter and work your way to the intake and look for anything that is blocking the flow of air into the engine.

You may also have a bad MAF sensor reading causing the ECM to think it has more air coming in than it really does. The ECM feeds more gas to not enough air, and you are running rich there.

 

My Canister is fine and checked it before. I would be able to smell gas also i think if it was bad. could be wronge. I am creating the vacuum leak on the back of the intake there the prong sticks out. There is one hose that goes to the brake booster and one hose that goes to the ac ducts and vent motors. I am disconnecting the one that goes to the vent and it runs so much better. But something isn't right. Any ideas?

 

If the screen was clogged up. Would this cause it to run bad also? Can you clean it?

 

Screen clogged=less air flowing through MAF, less air MAF sees, less air ECM adds fuel to.

If the screen is clogged, you may be able to use a small pipe cleaner and clean out the holes followed by a jet of highly compressed air to blow it clean, or just use jet air alone if you prefer.

 

If you have a air filter your screen isnt clogged.

 

Nope, not the problem. My rpm is still way down at 500 but sometimes goes up to 2000 and then back down to 500. Mostly it just stay at 500 and puffs bacl smoke. Any ideas guys?

 

It's either a bad can, (cold start) injector (many been going bad lately) or the timing is off, depending on where the black smoke comes from, but probably both. Smelling rich means too much gas and I quote: "my car has always smelled as though it is running a little rich and making a vac leak seems to make the rich smell go away" . Simple as that.

 

It can't be a cold start injector because i unplug it and the idle does not change at all. It is in perfect time and how could it get out of time? The can i took out the other day. the filter is fine and the can doesn't sound full of gas. I have just about had it with this car and i have spent about 1000$ into the engine! The engine should run awesome for that! I'm thinking about selling it but really don't want to. Any sensors i could check or anything?

 

i could get 2 whole running 3.4's for that much or less.

 

How to check an emissions control canister, according to my crappy Haynes manual:
1. Inspect vac hoses for kinks, leaks and breaks.
2. Inspect canister. If cracked or otherwise damaged, it has to go.
3. Look for fuel leaking from bottom of canister. If there is a leak, check hose routing and then replace canister if routing is correct.
4. Check for plugged filter at the bottom of the can. If clogged, replace the filter.
5. Apply a short length of vac hose to the bottom port of the purge valve (on the left side of the can when the ports are facing you). Blow through the hose. If any air gets into the can, replace the can.
6. Using a mity-vac, apply vacuum to the upper port of same valve. If it holds the same amount ofvacuum for more than 20 seconds, it's good. Next step.
7. Still holding the vacuum on the purge valve, apply a piece of hose to lower port and attempt to blow through the hose. If no air enters the can, the valve is clogged and the can has to go.

Other than the can, you can tell what the fuel mixture is by hooking up a multimeter to the oxygen sensor. The process for this is outlined in the Tech articles section. Have you checked the TPS yet with an analog multimeter? There are numerous ways to test each sensor, but you may want to have them professionally tested at an auto parts store, namely Autozone.

Unplugging the CSI doesn't make it stop leaking.. it just turns it off if it is running the way it was designed to. You have to pull up the injection rail, CSI and all, and see if any injectors leak when the fuel pump is manually turned on.

An engine can get out of time if the distributor clamp bolt is loose, but since it starts almost every time for you, I would assume that is not the case.