Hello all,

My 91 firebird formula has been stumbling at idle while in drive and sometimes dies. No matter what I try, nothing seems to help. I can drive the car around until it warms up then at a light while in drive it will begin to stumble and the idle surges to between 550-450 rpms and dies if i don't give it a little gas.

I have changed the wires, plugs, cap, rotor, coil, IAC & TPS (and set them to specs), reset the minimum air and idle to specs.

I checked for vacuum leaks under the hood and could not find any.

I had a small vacuum leak coming from the HVAC contols and I drove around with the vacuum lines off. It makes no difference if the vacuum lines are completely plugged or hissing away, the car acts the same.

Any ideas?

Thanks,

Chris

Do you have a TBI car?

It is a 91 formula 350 --- TPI (weren't all formulas TPI cars?)

Any suggestions??

-Chris

check you 02 seonsor sounds like it's a sensor problame... and tou CTS these could be bad or giving worng info which is bad. replace those and then see how it runs.. does it start up and idle fine for like a min or 2??

*cough*EGR system*cough*.

My WAG anyway. Does it happen only when it comes up to temp?

I would change the EGR valve, the air temp sensor & any sensor you can get your hands on. I started changing them all & I sware that every time the car would get better. At some point the car started to idle smooth and stoped shuting off at the lights.
Think that all of your sensors have been in use for so many years.

Thanks for all the replies...

It idles smooth and only does this once it reaches operating temperature. Does this rule out any sensors (I would hate to spend a fortune on several sensors when they are perfectly fine).

Does this indicate EGR? If so, why, and what do I change, the EGR valve or what? Is there a sensor related to this system?

Thanks again.

-Chris

I would, under no circumstance just start "replacing anything you can get your hands on"

You can check your egr valve before you toss money down the toilet. If it is the style of egr valve that has a vacuum line on it, you can get a small vacuum pump, like the ones you bleed brakes with. Connect the vacuum hose that comes from the egr to the pump, then start the car and put some vacuum to it. If the cars STALLS your egr valve is good, if it doesn't, then the egr and the port is prolly clogged.

I don't know about the the ones that are elctronically activated but I imagine you could find a way to jump the wires and make it open.

Here's my guess.

I'm thinking it's distributor related.