My 1994 Firebird 3.4Ltr runs rough under load and my cruise doesn't work & the ABS is showing a light "ABS Not Operable". Before it started running rough the cruise control was working but I could only make it work after 20-30 minutes of driving. Sometimes it seemed to turn on all by itself making my car accelerate. Then about 4 days after doing an oil change last May (I also put in a quart of Lucas Oil Conditioner) it started running rough but only after the first trip of my day. I replaced my SP Wires and it seemed to be OK for a week or so, then put in Fuel Injector Cleaner. At a loss, I re-changed the oil/filter. Again..the symptom disappeared for about a week then reappeared. Recently I replaced the Spark Plugs and SP Wires (they were all badly carbon fouled). That didn't solve it so I replaced all three coil packs then the Ignition Coil Module. Last item replaced was the Fuel Filter. I know the Air Filter is OK. It still runs rough. Some weird aspects of this symptom are...1) if I drive my car without warming it up first, or during very humid/rainy days the symptom shows up almost immediately..usually while going up a hill. 2) The car isn't throwing any codes or showing a SES light. I tried to make it flash the codes to see if any were stored and it wouldn't flash any codes at all. Not even a 12 code. I've tried unplugging some of the ignition sensors while the car was running and it didn't seem to make any difference nor did it show or store any codes. I haven't used a OBD1 code reader on it but my manual says it should flash the codes when the A and B ports are jumped so that's the method I used. I haven't replaced the PCV valve since I bought the car and I've put on 35K miles. I don't know if the EGR has ever been checked or serviced. The car has 150K miles on it. When it's not running rough (first trip of the day) it seems to run very well. I never have any problems starting the car. After the symptoms appear the idle is rough but the RPMs seem to hold just fine. I'm starting to suspect a vacuum leak or a bad PCM but it seems like if the PCM was bad then the symptom would be constant. If anybody has any suggestions or has had a similar experience and solved it Please let me know. I'm running out of funds for this problem. Thanks, Robt.
 
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