u/LoveHarambe

Short version: 944NA runs fine but sometimes, while idle, suddenly starts running really badly. Restarting after this is hesitant, but then it runs fine again.

Long version:

I was on my way to MOT a couple of weeks ago, and while waiting in the queue, idling, it suddenly started running really badly. It was a really drastic change, normally it idles well, but suddenly idle dropped to maybe 500 rpm and it stuttered. I turned the car off and tried to restart it. Had to crank it multiple times and it finally came to life again, first running badly for a couple of seconds but then running well again. During the MOT inspection the car was turned on and off multiple times without issues and I had no trouble on the drive back home. So I didn't think too much of it, maybe a bit of bad gas or something? It passed MOT by the way 😂

Today, I went for a drive again and it was hard to start, it took quite a few cranks and first ran badly for a couple of seconds. Since the car has been sitting for some weeks I wasn't worried, but it normally starts up right away.

Then 30 mins into the drive, it suddenly hesitated again for a few seconds when idling, but it recovered by itself. I then went home, no issues.

Did anyone ever experience something similar?

I was thinking something electrical, fuel or ignition related, since it's so sudden?

I have replaced and tested many things since buying the car two months ago, such as spark plugs and leads, ignition cap, speed and reference sensors, fuel filter, injectors cleaned, fuel pressure tested.

I didn't replace the fuel pump (since pressure seems ok and it's running fine under load). I also didn't replace the ignition coil. Could any of those be the culprit?

Cheers!