What Would Cause This ??

[97LT1Z28]

My engine has a rough idle. When I accelerate, the motor shakes for 3-4 seconds than it corrects itself and takes off. When this happens, it sounds like the timing is off.

The ECM is giving me a "Random Misfire" code.

I've already changed the following:
• Rear O2 Sensor
• The Entire OptiSpark Distributor including the Cap & rotor, optical sensor, all seals including oil seals beneath the opti
• Water Pump
• Spark Plugs
• Wires
• Ignition Module
• Coil
• PCV
• Checked for both Vacuum leaks and Exhaust leaks - there are .

What else could be causing this?

[blackthunder50]

Maybe one of your plugs failed early. I remember a plug failing on our explorer early, it had the same symptoms as your engine.

[96Camaro]

I know my car doesnt have a pcv valve...its just like an elbow thing.

[97LT1Z28]

I wish it were a single plug - the ECM is showing a random misfire though...

[Trash man]

fuel injector having an issue?

[Injuneer]

I know my car doesnt have a pcv valve...its just like an elbow thing.

You're wrong. Your PCV valve is located on the drivers side of the intake manifold, near the center. The line on the passenger side valve cover, with the plastic elbow is simply the line the supplies the clean filtered, MAF measured air that the PCV system pulls through the crankcase and lifter valley.

I would suggest an injector, possible leak in the EGR system (did you check the hole for the EGR pintle for carbon when you replaced the valve?), a vacuum leak. The after-cat O2 sensor has nothing to do with how the car runs, so that's insignificant. What about the two pre-cat sensors? Have you checked those? What about looking for a vacuum leak? Any possibility of an exhaust leak before the O2 sensors? How about corrosion at the Opti harness connectors.... including both the one at the Opti and the gray one on the clip on the passenger side of the intake manifold? Is it possible you have the injector harness clips on the wrong injectors (they are numbered)? Do you have the intake manifold leak, at the rear of the block, right below the EGR riser tube?

Have you had a "complete" scan? Although the code is for random misfire, the PCM also keep a count of the misfires on each cylinder. Have you had those scanned (requires a scanner with "enhanced parameters")? Possible you have a burnt valve, a sticky of collapsed lifter? Have you checked the quality of all the ground strap connections on the engine? Have you put is on a scope and checked the pattern of the spark to each cylinder?

Does a scan show any irregularities or imbalance from bank to bank in the long term fuel corrections?

You haven't even scratched the surface yet.

[97LT1Z28]

Fred . . . Thanks for all the suggestions.

You're right, I haven't even scratched the surface yet.

I'm going to do extensive checks for a vacuum leak using the methods that you've discussed in previous strings.

Then, I'm going to get an extensive scan and hopefully zero-in on the cause.

Thanks everyone for your help on this and I'll report my findings soon!

[93/96 f-body]

random misfire code

I'm having the same problem.My car misfires under a load at low rpms.And i've pulled the same code.I only have 26,000 miles on it and it's a 96.I took it to a shop to have it fixed and the guy didn't help me much for $160.00 he found misfires on four cylinders mostly number five and the vaccum checked fine?I tried a used plug & wire on number five and it didn't get and better.I'm guessing from not driving it much its a dirty connection or a egr leak from my past header install.I've changed the coil and egr valve also.If i have time soon i hope to figure it out so any input from your adventure will help.

[Joe 1320]

Get car into a dark environment, open the hood and start the car. Any igntion voltage leaks will be visible as blue glow around plug wires and connections. I've seen many cases where the metal boot shields cause a misfire.

[97LT1Z28]

Get car into a dark environment, open the hood and start the car. Any igntion voltage leaks will be visible as blue glow around plug wires and connections. I've seen many cases where the metal boot shields cause a misfire.

I'll do that and report my findings on that too - thanks for your help guys!

[93/96 f-body]

update

Just reporting back.I just found a loose header bolt on the passenger side rear and also after shutting the lights off as explainded before found a bad plug wire which looks like its rubbing the header.So take a close look.I missed both problems until taking a closer look.I hope to get to the plugs and wires this weekend and hopefully my problems are solved.Good luck.

[97LT1Z28]

Update: The severe, intermitent miss is still happening. I got the car in the garage at night - pitch black and started it up. No voltage leaks or arching at all. I also cleaned out the EGR valve - there wasn't much build up at all. Next, I'm going to replace both front oxygen sensors and then I'll report the results. Thanks for all your support so far!