DaveK

Very easy - once you've taken the front off with the filter, the airbox is attached to the AFM with four nuts. It's also secured to the engine in a couple of places - one nut in front of the airbox (which I'm sure you've seen) and another one inside the airbox, which is also visible when you've removed the filter.

Vandit

Old thread bump, was this sorted? What turned out to be the problem?

StanUK951

Hi Vandit, it was eventually yes. I had the O2 sensor and cylinder head temp sensor changed at the same time and that cured it. Not sure which of these it was though...

Vandit

Thank you for the quick response. Yes, unfortunately I'm dealing with a similar problem.

I first experienced it in Dec while driving to and from an autocross, but the car raced great all day with no issues. I didn't drive it all winter due to other wrenching projects on the car, and replaced the coils, caps, and rotors during that same period. All components looked tired and due for replacement. I've been driving and racing the car again since April and thought I had solved the problem but it has shown up again during the last couple of times I've driven it to work. Today was exceptionally bad because it totally cut out in stop & go interstate traffic as I was getting going in 1st gear and the car actually stalled. Usually it'll do it while I'm already moving, so while it still loses all power for a moment (feels like an eternity), at least the car doesn't actually die like it did today.

StanUK951

It's awful when you can't trust your car... I saw a 993 yesterday stopped in the middle lane of the A406 (busy ring road around London). Was just waiting to be rear ended.

Try the things I mentioned and I hope it fixes it for you... Let us know how you get on.

Richard Curtis

Vandit: try cleaning the ground connection between the battery and the body. Mine had similar problems and this cured it.

Vandit

I had cleaned the ground near the battery some time last summer when I took apart that area to do some minor corrosion prevention. I went ahead and took apart the ground point again this morning and cleaned the body side and contacts w/ some fine grit sandpaper.

I also order a new Head Temperature Sensor from Pelican this morning.

Earlydays

I had very similar symptoms a few years ago and it was only the DME relay

Vandit

I've swapped DME relays and that didn't seem to stop it. In fact, the first time I experienced the problem, I immediately pulled into a gas station and swapped the relay.

I drove the car to an autocross on Sunday and getting to the event I felt the misfire maybe twice, very subtle, not a big deal. I pounded the the car all day and it never missed a beat. Ran great. I drove it back home like normal and it started to act up pretty bad. It seemed worse when below 3k RPM while giving it light throttle (i.e. typical expressway driving conditions).

I ran into another 964 owner at the autocross and he suggested I clean out my ISV, so that's another item on my to-do list.

Vandit

I cleaned the ISV last night and drove the car this morning and it acted up again.

I've figured out that if I keep the cruising RPM in a higher range (over 3k), I can keep the misfire away for the most part.

The new CHT sensor should be delivered today, so hopefully I can swap that piece by this weekend.

Vandit

Replaced the CHT and the car started f'ing up like usual almost as soon as I pulled out of the driveway... Not a happy camper right now...

Steve Weiner-Rennsport Systems

How old are your plug wires??

Are you sure they are all seated correctly at the plugs & caps????? (this is a biggie)

How old is your O2 sensor?

Did you check the whole intake system for vacuum leaks??

Vandit

I do not know the age of the ignition leads or the O2 sensor, I assume they're stock.

I've done the water misting in a dark garage from the topside and bottomside w/ no indication of arcing of the leads.

The coils, caps, and rotors (all Bosch) are new, all wires are seated.

How would I proceed to check for vacuum leaks?

Robbie Ravioli

Try spraying brake cleaner around the engine. Due to the vacuum in the manifold it gts sucked in, and it being combustable you hear the engine running better/rich. I usually measure the lambda signal response (wide band lsu), but it is pretty clear from the engine tone.

Robbie Ravioli

I am having an similar issue myself, below 2000 rpm the engine doesnt run as smooth as it used to. Spark seems strong, but I am not sure about he fuelling. Timing and cams are all ok. I was going to add a lsu to measure the lambda, but havent got round to do it.