Car was totally fine then all of a sudden while driving car started shuddering badly on idle and under acceleration. No CEL and no codes! Engine is weak as well felt like running on 1-2 cylinders only but was still able to drive car to work and back. Coils and plug are fine. No vac leaks. Now where do i start? Im totally clueless. Will Bad injectors or pump throw codes? Please help. TIA

 

Okay i did the typical switch plugs and coil packs. Cylinder number 2 is not firing at all. Also the plug that originally was on cylinder 2 is wet but fires and is okay if i switch it to a different cylinder. Now what would be the cause of this? I stumbled upon this write up http://wiki.quattroworld.com/index.php/A4.B5.DIY.Ignition.DIYTestPOS could it definitely be a bad N122 or ICM? Anyone else have this experience? TIA

 

Pull the codes and see what they say.

 

No codes at all... Which is really weird! forgot to mention it is a 98 a4 1.8t quattro if it helps.

 

That certainly sounds like a vacuum leak to me.

Do you have a boost gauge? Have you tried spraying carb cleaner in and around the engine bay (while at idle)?

 

It's very odd that there are no codes. A misfire - for any reason - should throw an OBD code. So should a vacuum leak.


Is the timing belt happy?


Can you get some VAG-COM codes? Those will show far more than an OBD reader.

 

A serious leak in the PCV system can cause these exact same symptoms, w/o throwing any codes, but like mtroel said: If you're getting misfires and not throwing codes, that's odd.

If that's the case, you might be looking at the ECU.

 

Okay sorry it took me a while to get back to you guys about this issue. Since im from the Philippines it took almost a month to get my part and post feed back. It is just simply the ICM. I replaced that one and all is fine. ECU is fine and i just prolly didnt drive the car long enough for it to throw codes. But im glad all is good now. Thanks for everyone's opinion and thoughts. I appreciate it.