I have a 1991 Camaro RS with a 305 TBI and Automatic transmission. Im having a problem with the fuel being shut off after high idle. This takes place after the engine goes from about 1000RPM to 500-600RPM. The fuel shuts off completely. I know this because I checked the injector umbrella and there wasnt any.

Ive replaced the IAC, EGR, MAP, ECT and O2 sensors already. The problem only occurs when the engine goes from high idle to low idle, and it does it in and out of gear.

Does anyone here have any experience with TBI smallblocks that can help?

What codes if any are present?

First thoughts:

Will it stay running if You hold the RPM's up with the throttle?
If so, that will eliminate the VATS as a problem.
If it does not stay running with the throttle held open, what is the security light doing ?

Thats the scary part!!! Theres no trouble codes! Not only that, but if you hold the throttle, it doesnt help any. Im scratching my head on this one. I used the paper-clip trouble code trick, and none show up. Only the 1...1,2. 3 times (indicating, no code)


I hope maybe someone here has a clue, because I sure dont!

Some of the sensor parts are cleanable. The lincoln lsc I have has a mechanical part for one of the sensings that gets dirty and will give you a searching idle if while not in gear then doing a rev. The rpm goes up and down for a while and normally one of the downs is an engine shut down. Maybe look for a part that has a lever sticking out of it and something like 4 screws holding the plate the rod or lever goes into. Mechanics say $100 while experience says tinker with it.

I'm not sure about your particular motor, but wanted to mention that a bad crankshaft position sensor or camshaft position sensor can cause this. Like I said, I'm not sure if your engine has these sensors. In some cases, the only sensor is the camshaft sensor which is essentially the electronic pickup in the distributor. Consult your service documentation for details.

I've seen crankshaft sensors do this before. The computer turns off ignition and fuel to the motor while cranking the engine. Once the engine detects pulses from the crankshaft sensor, it enables the injectors and ignition. This is done to prevent flooding when starting the motor. I wonder if at low idle, the sensor signal drops out and fools the computer into thinking the engine has stopped rotating and turns off ignition and fuel.

See if your service manual explains how to test the sensor. It's also possible that it needs adjustment. In any event, it would be nice to ensure it's a problem before replacing the part.

-dnult