vandiemen17

My 87 Trans Am 305 TPI idles fine, starts right up. Drops off at any throttle position. Changed MAF, TPS, Fuel Pressure Sensor, Distributor Cap, Rotor, Plugs Wires, Fuel Pump, Fuel Filter, and all Vacuum Lines. I am at a loss. HELP

vinny R

Have you changed the ICM? It located at the bottom of the distributor and it controls the spark advance..

vandiemen17

ICM is new also. The more I work on this the worse it runs.

Vader

Fuel pressure sensor? Di you mean to report regulator? There is no pressure sensor on the vehicle, and they didn't appear until the mid/late 2000's on a few vehicle models.

Speaking of fuel pressure, can you report the pressure measurements?

vandiemen17

You are correct fuel pressure regulator. Pressure is 40 to 45 psi.

vandiemen17

I'm thinking maybe the EGR valve.

jkris53406

iTrader: (5)

The egr will only open off idle. If it were malfunctioning qnd suck open, the engine would be doing the opposite and only run at speed. The car would not idle at all. Weak coil perhaps?

vandiemen17

Thanks for the info on the EGR, one less thing to replace. The coil is new along with cap rotor and ICM. If I can get her out of the garage it's going to the shop.

goldandblue

So i had a friend with an early 90s gmc jimmy. Very similar situation. Ended up his cat was stopped up.

vandiemen17

I'll pull the darn thing and see what happens. Thanks

ascamaro

I pulled the cat and the problem still exists.

Car starts right up and idles fine. Opening the throttle the RPM's drops off and the engine surges. Feathering the throttle I can get the engine up to 3000 RPM, but opening anymore will cause the engine to surge and drop off. I can drive the car slowly by playing with the throttle. The Fuel Pump and Fuel Filter are both new, along with all the Injectors. I have changed the Fuel Pressure Regulator, the pressure at the fuel rail is between 45 and 50 psi. The Mass Air Flow and Throttle Position Sensors are both new. I have changed the Distributor Cap, Rotor and ICM along with the Coil, Spark Plugs and Wires. I have no trouble codes.

I am at a loss as to what to do next.

Annihilate

iTrader: (1)

Maybe invest in a scanner and try to get a live readout of what's going on. I use a portable bluetooth scanner from this guy http://www.1320electronics.com/ very helpful as well.