Erratic Idle/Power Loss

[Shawn24]

I drive a'91 Camaro Z28 with a 350 5.7 liter tuned-port injected engine. I bought it less than a year ago after vehicle sat undriven for an undisclosed amount of time.

No alterations to the ECM have been made, and all engine components are included. However my emission system has an after market edlebrock duel exhaust cat-back system with the catalytic converters removed. This system had been installed for several thousand miles before the problem began.

Approximately 10 seconds after I started it one morning (it had not been driven for 10 or more hours and it was about 55 degrees outside) it began an erratic idle with loss of power. I was still in park. I noticed later that my intake manifold gasket was blown. I proceeded with a full tune-up (distributor, rotary button, plugs, wires, coil, cap), replacement of all upper end engine gaskets and a thorough examination of all vacuum lines. I also replaced the fuel filter. The problem persisted.

I then replaced my TPS, ECM, and MAP sensor to no success. Nor more trouble codes are stored in my ECM. The car now runs even worse and even sprays unburned gasoline out of the tail pipe. There is a massive loss of horsepower.

What should I do?

[wrightz28]

Secondary igntion system failure (misfire) would be my first guess, ICM or pick up coil?

[Shawn24]

I'm not real versed in 'mechanicese', so I am not sure of your question. I do have a 50,000 volt Mallory coil mounted externally (not on the distributor). Does that answer your question?

[Shawn24]

The car has a tuned-port injection system. There is an individual injector on each cylinder. If one or more of the plugs is bad would the fuel potentially not ignite and cycle through the exhaust system? Please keep in mind that it is burning excess amounts of fuel. Could a hung open EGR valve cause this?

[wrightz28]

Fuel injectors are batch fired on these, so yes, if the plug is fouled, the injector is just going to keep on spraying.

The ICM - ignition control moudule is a notorious problem maker, it's just a electronic version of the old points and condenser distrubuters. The pick up coil is basiclly a crankshaft position reference to determine engine speed and position of stroke cycle.

[Morley]

Pull the vacuum line off of the fuel pressure regulator. If you get fuel (any amount) out of it, the regulator is shot and needs to be replaced.