I've got a 3.4 with a 4.3 TBI and I'm having an intermittent problem with it stalling and erratic idle. I just had the fuel pump go out and I got a free used one and put it in and it started right up so I'm sure that was the problem then. I did wait a week or two to change the fuel filter but the old filter was only a couple of years old. I've got a new TPS and I'm going to reset the minimum air. Does anyone have any other ideas, Could the MAP Sensor or Idle Air Control Valve have anything to do with this. Any help would be greatly appreciated. Thanks,

Bill, hopefully getting the minimum idle speed and TPS voltage adjustments dialed in will help with the stalling & idle issues. It did on mine.

If the EGR valve was intermittantly sticking, it'd cause stalling at idle. Something to check out, anyway.

I'd look for vacuum leaks. Also inspect the vacuum lines for cracks, and to make sure they're properly routed & plugged-in.

HTH..........ed

Ok I need more help. I finally got around to working on it, I was going to take care of the TPS and see what happened. It had sat for a week or two without being started and I needed to move it outside where there was more light. It would not start. I couldnÆt find any trace of fuel in the TBI (I didnÆt have anyone else to watch while I was turning it over) so I figured that used fuel pump must have gone bad. How lucky can I be! Just to be sure (before I spent 200 bucks on a new pump)I thought IÆll spray some carb cleaner in the TBI and see if it tries to start, well it did and it ran real rough long enough for me to get out and spray some more in there. It continued to run rough for another moment or two and then it started to run on its own and then it eventually smoothed out and ran pretty good. The spray pattern on both injectors looks real good. Is there any thing that would cause the injectors not to open up or work at first, on start up or when itÆs cold? Even though it started to run on its own long before the engine had a chance to get warm. Thanks,

I had nothing but problems with my idle air control valve. I replaced it more than once hoping to correct the same kinds of issues you are describing. I also tested, adjusted, and replaced all sorts of things (Throttle positing sensor, MAF thingy, etc.) and never could get the IAC valve to function properly. Finally, I made it close all the way and then I unplugged it. Car has run like a champ ever since. I'm really not even sure what the thing does. I think it helps your car to warm up faster by making it idle higher when the engine is cold.

As fare as I understand the IAC, it is actually a bypass for air from your intake to make it down in your engine. When you are idling your throttle plates are pretty much closed, but the engine still needs air, so the valve open ups the bypass to let more air in and keep the engine from dieing.

When I got in it the next day it started just fine when cold. Didn't drive it so I didn't experience any of the problems. I was thinking about the fuel pressure regulator, if it was going bad could it cause my problems. I don't even know what it looks like or where it's located. Any Ideas guys? Thanks

Bill, the pressure regulator is built into the TBI unit. You have to pull the entire injector "pod" to access the regulator.

Here's a link to a pressure regulator repair kit at Partsamerica.com:

http://www.partsamerica.com/product_images/img/nie/21732-1.jpg

It sure sounds like some freak thing, who knows whether a sticking regulator, probls with the injectors, or bum connection in the EFI circuit might cause that to happen??

Maybe you'll get lucky and the problem won't repeat!

If it does, you may need to pick up a couple of those injector test light thingamajigs (if that term is too technical, try "Noid Lights"!) that will tell you whether or not you're getting injector firing voltage from the ECM.

Here's a few more links to tickle your fancy:

http://www.toolmancentral.com/Fuel_System_Accessories-c1339-pg4504.htm

http://www.goingfaster.com/spo/tbi.html

http://www.cfm-tech.com/catalog/tbi_injector_install_kit_684301.htm

http://www.witchhunter.com/

HTH.....ed

Thanks Ed, is the pressure the same on both the 2.8 and 4.3 TBI. If not should I repair/replace it with the 4.3 since that it what the injectors are?

Bill, fuel pressures are the same regardless of the size of TBI. The difference lies in the injectors' flow rating (in addition to the tuning of the ECM for any particular engine C.I.).

Of course, fuel pressure adjustments to the stock regulator are possible within a limited range, to effect tuning needs. Aftermarket mfr's even offer an adjustable fuel pressure regulator, which allows a broader range of pressure adjustments. Check out these links for more info:

http://www.aces.edu/~parmega/efi/tbi_adjust.htm

http://www.cfm-tech.com/gm_tbi_fuel_pressure.htm

http://www.turbocity.com/product_info.php?products_id=437

The Niehoff rebuild kit fits a range of TBI's including 2.8 and 4.3. Check this out:

http://www.partsamerica.com/ProductGuide.aspx?mfrcode=NIE&mfrpartnumber=21732

Before you tear into things you might drive it for a while to see if the problem repeats.

You could pick up one of those "noid light" kits, and if the problem does reappear, plug-in the lights to the injector connector, crank the engine over and see if you're getting firing voltage. That'll tell you right away whether it's an electrical or mechanical problem.

If you're getting voltage to fire the injectors but they're not spraying, then you've got fuel pump/pressure issues or something in the TBI itself.

Fuel pressure test kits are available to check your existing pressure; that may tell you a lot about what's going on. Lots of these at eBay and elsewhere.

Here's a Google search for that:

http://www.google.com/search?as_q=GM+TBI+fuel+pressure+gage&hl=en&num=100

G'luck.........ed

I had a few issues with my truck after I built it , so I put pressure guages on myfuel lines.I have one under the hood and one in the cab so I can watch my pressure as I drive.

It turned out to be the fuel pump I had was the wrong one , it wasn't for EFI , so the truck would have idling issues and stall out of nowhere.Took me a few times of it happening to figure it out , and once I saw what was happening on the guages where the pressure would drop from 12 to 8 , that was the problem.Put in a new pump and never had another problem.