Marv

I have been getting random misfires for some time now.

Original codes were P0300, P0301, P0302, and P0304 (cylinders 1, 2, and 4). The latest were just for cylinders 2 and 4.

I replaced all six coil packs and plugs in January. Old plugs look all the same, no obvious differences or problems, but I have received two CELs now since that replacement, one shortly after the install, the other yesterday at the autocross track.

I'm not sure what to look for now. I think the car does idle a little rough, but that's somewhat subjective. There are no noticeable misfires.

Car has 135K miles.

pete95zhn

Clogged injectors? Symptoms sound so familiar.

32krazy!

Plug gap

Marv

I didn't set the plug gap, but if memory serves, don't the plugs have something like three tongs on them? Should they be set and to what?

I thought plug gap was something you did in the 1970s and 1980s?

Also, the problem existed prior to putting in new plugs and the same cylinders have misfires before and after the change.

The DareDevil

Stock cats?

Marv

Yes.

The DareDevil

In my situation, the cats (aftermarket) loosened within their canister enough to restrict exhaust flow. At high RPM, I was getting random misfires on all cylinders.

Marv

I hadn't thought of cats. We have two; one cat lives inside and the other outside. Maybe one crawled in?

All kidding aside, I was thinking injectors and poured some Techron in the tank, but given the number of miles, cats are a real possibility.

What makes this even more difficult is that the rate the codes come up is very low, once every few months.

Gofishracing

maybe
Symptoms of a Faulty Mass Air Flow Sensor
A faulty mass airflow sensor will cause problems similar to low compression or low vacuum, and will also show symptoms similar to when your vehicle has low fuel pressure from a faulty fuel pump. Here are some of the most common symptoms of a faulty mass airflow sensor:

• The engine is very hard to start or turn over
• The engine stalls shortly after starting
• The engine hesitates or drags while under load or idle
• Hesitation and jerking during acceleration
• The engine hiccups
• Excessively rich or lean idling

WBaransky

None of the symptoms apply to my situation. It would have been so nice to resolve. I do smell fuel once I return to the garage, but thats about it.Appreciate the comments and symptom check. Great stuff

Marv

How many miles on your car. My misfires were due to low compression in several cylinders, which turned out to be worn valve guides. Now I had a lot of miles on my car (143K) and your situation might be very different.

WBaransky

Mark, my car has 45k on it. Probably not worn valve guides. But thanks

WBaransky

Sorry, meant Marv.

Marv

Yeah, I agree, but you might want to have a compression and leakdown test if you still can't come up with a cause.

How are your vacuum lines? Even with low miles those plastic lines get brittle with age and will crack.

WBaransky

Thanks Marv, will have that checked. Will replace oxygen sensor, give intake a good look for a small vacuum leak and try to clean blow out the secondary air system....thru my Porsche specialist. Will see what that does.