94 firebird 3.4 runs rough

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I'm new to this forum and am my wit's end with my girlfriend's car.

1994 Pontiac Firebird 3.4 v6, at.

The car started running rough a few weeks ago and gets really bad gas mileage (about 10mpg).

Recently, I have changed the oil, spark plugs, O2 sensors, belt, tensioner, alternator and fuel filter.

In trying to troubleshoot the car, I have checked the oil (not burning), replaced the O2 sensors, checked spark plug wires (ok), checked the air filter (ok), run FI cleaner, reconnected a disconnected wire under the car (may be the rpm sensor for the coil pack), reset the computer (disconnected the batt). The last thing I did was replace both O2 sensors. The car ran bad before I did that and now g/f says it's worse! I wanted to replace the EGR valve, but at over $200, I need to know he old one is bad and I was told that a bad EGR will throw a CEL.

Any help is greatly appreciated.

posted by  rotus

Hey rotus. I don't know if anyone ever got back to you on this.

I had a stumble in my '95 pontiac, same 3.4L engine, and it turned out after much expense (plugs, injector cleaner, wires, o2, banging head against fender, the whole 9 yards) I found out I had a defective ignition coil pack. Have you checked those at all? There are three at the front of the engine, and they should have corresponding cylinder numbers stamped on top. The resistance check for these in the Haynes manual didn't show the problem - they look fine as far as that goes - but once I replaced two out of three, all stumbling was gone. If you're getting 10mpg, that's horrid - that little 3.4L is capable of pushing out 30-36 mpg with 91 octane.

posted by  pugsley

Did this thing every trip an error code with the onboard computer? 10mpg is very bad...almost as bad as "limp-mode" (where the computer's sensor(s) fail to the point of working on 'pre-sets")


posted by  TedyBear

the map sensor is not working and your mixture is way off.if you tap on it lightly and the rpms change or you blast it with 5 second shot of freeze spray
and it does something ,its junk.i would just change it .check and make sure that you do not have a vacuum leak...

posted by  the lobster

trouble codes? Looks like folks love to spend money supporting the stockholders of Autozone, Napa, etc. with out figuringh out whats wrong with the car.

posted by  tbaxleyjr

gotta agree, there. take it by autozone, have them pull the codes for free, and get back to us

posted by  dodger65

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