Hi there,
I have a firebird 91 that sometimes goes ok and others not that good.

When I turn on the engine, specially when it is already warm, the rpms go to 1500-2000 rpm suddenly and then go down again suddenly to 500-600 rpms. This is the indicator that things are not going to be ok for the rest of the trip. When stopping the car the rpms go to 500 bouncing and going back to 1000 and oscillating and so on, so that the car stalls but doesn't die. If you keep on driving like that some more time the light of service engine soon comes on.

I keep on doing the oil change every 3000 miles. And I changed the fuel filter 1000 miles ago. I have only had one problem with a failure of the alternator, and I am starting to think that such a non uniformity of spin when idling can cause another failure in the electric system.

The light will turn off when turning on the engine again, so I don't know what to do because if I take the car to have a readout the most probable thing that is going to happen is that the light wouldn't be on when cheking.

Any ideas?. I have thought about changing the plugs and wires, anybody knows how much should they charge?.

Thanks.

 

What this sounds like is possibly a vacuum leak. I am assuming the car runs just fine when cold but as soon as the engine warms up and the idle drops the computor starts trying to compensate and maintain a steady idle. This problem could also be the throttle body being dirty as well. It is important to note you need to use throttle body cleaner (NOT CARB CLEANER) for cleaning your throttle body, or intake. There is a film on the inside of your intake that carb cleaner can remove and possibly get stuck on your valves.

 

Thanks!. When I said that it happens when the car is warm I meant that the first time you turn on the engine after a day or so of the last usage, the car is running ok without any problem. But if after the start you go somewhere, park and turn it on again it happens the weird thing that I told you. It seems that a vacuum leak should also happen in the first period when the car is started from cold conditions, doesn't it?.

 

Not usually because the injectors are dumping more fuel when the engine is cold plus the computer is in open loop to help it warm up. You should notice any problems as soon as the engine warms up like in 10-15 min.

 

The cause of the light on turned out to be the Oxygen Sensor. I got it replaced and it does not do the weird things when stopping at a traffic light. The idle is still rough though...