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Q: My 1994 Firebird 3.4Ltr runs rough under load on 1994 Pontiac Firebird

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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HERE'S an UPDATE... Next thing I did was to replace the air filter and then the PCV Valve. The air filter turned out to be quite clogged even though it looked fine. There were pine needles stuck between the folds of the filter and I didn't see then until I took it out and tapped it hard. I replaced it and the PCV. I then noticed that the PCM has to be has to be reset by unhooking the battery whenever any of these types of jobs are done. This is when I really started making headway. When I replaced the PCV Valve, I discovered it wasn't snapped all the way into it's grommet so I replaced the PCV and that fixed a vacuum leak. I then discovered that many of my crankcase vacuum and vent lines/ pipes weren't all installed properly (there's a Crank Case Vent Pipe that runs from the RH valve cover to the rubbery intake duct). I fixed those and things improved even more but it still ran rough under load after warming up. Then I checked the Secondary A.I.R. System. The AIR Pump fuse was blown when I check it so I replaced that and it held. The tiny pressure hose that activates the A.I.R. check Valve was also kinked. Fixed that. Then I took your advice and took it into a professional shop to have the EGR and O2 Sensors checked and get a diagnosis. They took $150 from me, replaced two parts that I had just replaced, and told me the coils in my fuel injectors were bad. Took my car home and tested my injectors resistance. they were perfect. Right within range at 12.7 ohms. Then I started suspecting a exhaust leak. Took my car in to have my O-Rings (exhaust manifold-to-head pipe gasket) replaced. THIS was a honest mechanic. He told/showed me that neither of my O-Rings had failed and took no money for doing it. I then read up on my car's digital EGR system on the Internet. I found a site by that said my EGR had a common failure at the assembly gasket. they said the 3 screws that hold the device together should be tightened to avoid EGR leakage. So, I did that and the problem disappeared. I then found another advice online that said my ABS INOP light might turn off if I just replace the high/center brake lights in my spoiler. That totally worked too. ABS in fine now just by replacing two light bulbs for $5. This problem was a intermittent rough running (or misfire) under load after reaching normal operating temperature issue. I wanted to report all my fixes and the final solution because I think a lot of Firebird/Camaro owners seem to have very similar or exactly the same problems with their 4th Generation F-Body GM Sports Cars. Thanks for your advice. I actually came to this site to avoid using a mechanic as cost of this fix was a major factor for me. Here's the PDF webpage address so anybody can look at and read about this EGR for themselves. I know they used this digital EGR on many many makes/models of GM cars and trucks.
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