First off i have googled this hundreds of different ways and went through pages and pages and couldn’t find anything on this.

Sorry this isn’t about a DSM but i really need help on this and you guys are definitely my best resource for cars.

Ok so my friend has a 98 chevy lumina (auto) and has a misfire on cylinder 5.
The plugs and wires were recently changed.
The really weird thing is that when i erase the code the misfire goes away
Then it will be totally gone (No shaking no CEL no nothing)
It will come on again at a totally random time.

1st time i erased it he moved the car back and forth and nothing then we floored it up the block (not passed the speed limit) to put a good load on it and nothing then when he was driving it on the highway it came on.

2nd time i erased it it just came on while he was driving down the street.

So im pretty baffled by what it can be.

I was kinda leading towards a bad ecu maybe? I’ve heard that chevy ecu’s are trash but correct me if i’m wrong.

Any help will be greatly appreciated..

I would lean more towards a bad crank sensor, or even bad wiring to the sensor. A good practice is always to check the connectors inside the engine, regardless of whether or not you think it has anything to do with the problem.

+1 for the crank sensor, my old 420a DSM had a phantom misfire code that turned out to be the stupid $25 crank angle sensor.. After throwing $1k worth of other parts at the car.. But that's where I would start, any sensors that tell the ECU where the engine's at, before looking at the big ticket parts.

what engine is in it? 3.1? 3.4? or a 3800?

Please post the code(s) that you found, and as BogusSVO said, post the engine size.

the ignition control modules and coil packs are notorious for going out in the GM v6. The ICM heat soaks with under-hood temps and will fail intermittently. In some cases, it's just to one coil.

The good news? You can pull the ICM and have it tested at Advance/Autozone. Be sure to test it 2-5 times in a row though, as on the first go I've had plenty of them test fine until we kick some heat into them.

Thanks alot for all the reply’s guys.

Its a 3.1 and the code (only one) is P0305.

OK, that code is Random Misfire, Cylinder 5 if my memory serves me right. I have a huge headache so forgive me if I am wrong.