TEF1701

This may seem like an elementary question, but what will cause the timing mark to bounce around by 2-5 degrees? My timing mark will be mostly steady for a couple of seconds, then my idle goes rough, and the mark dips by as much as 5 degrees. I was always told that worn mechanicals in the distributor can cause a bouncy timing mark. Whatever it is, I think it's contributing to my rough idle and obvious misfire. Where the heck should I start?

TEF1701

I'm still trying to track down the cause of my crazy, bouncing timing mark and rough idle, hesitation, etc. I pulled the plug on my knock sensor after it had warmed up (don't worry I didn't drive without it plugged in), and it didn't change anything. In my past experience with fuel injection cars, when you pull the plug on some part and the engine either runs the same or it runs better, that part is often bad. My Bentley says nothing about how to test the knock sensor, so...... what the hell? I don't think the rough idle and erratic timing is a coincidence. A new knock sensor is only $35, but I don't want to go replacing random parts in the hopes that it fixes it. Just need to bounce some ideas off of some other people, especially now that the weather is warming up.

UPDATE:
I've read on other forums about the 2.3 NG engines being EXTREMELY picky about the type of plug they use. The originals I pulled out when I first got the car were the Bosch W7DTC triple electrode. I replaced them with standard Bosch Platinum plugs because I couldn't find the W7DTC anywhere. I can get the NGK BP6ET or the Beru 14-7 DTU though. I use nothing but NGK in my Toyota, and I love them. I will die if it's something as simple as a spark plug issue, but I've seen crazier things. Any opinions on this?

TEF1701

Anyone home? Feels like I'm writing a blog instead of posting on a forum

I got impatient and swapped out my single electrode Bosch plugs with the NGK triples and new Bosch wires, and the car actually runs slightly worse. Seems to idle about the same, but the hesitation while driving down the road is worse. It does seem to accelerate better though. So bizarre. I'm going to recheck the timing today and post the results. I'm hoping that maybe I had adjusted my timing to compensate for the misfire caused by the wrong plugs, just like people who adjust timing and fuel mixture to compensate for a vacuum leak.

What I've done so far to track down the misfire issue (in no particular order):

1. Professionally cleaned fuel injectors
2. New intake gaskets
3. Checked all vacuum lines
4. Sealed cracks in intake boot and reseated it properly
5. New plugs and wires (cap and rotor look fine)
6. Unplugged knock sensor (no change better or worse)
7. Unplugged idle regulator valve (ran way worse and almost died)
8. Checked fuel pressure before and after pressure regulator
9. Replaced temp control switch
10. Pump, filter, and accumulator all replaced
11. Set timing to factory spec (before new plugs)

TEF1701

Okay, I QUIT! I am a complete idiot. I have had the timing set WAAAAAY wrong this entire time. There are apparently TWO marks on the flywheel: a line which is to be used with regular timing lights and a "0" mark for a timing light with an advance. I set it using the line, with my light set to 15 degrees. That's right, my timing has been off by a lot. Not a little, a lot. For anyone setting the timing on these cars, USE THE CORRECT MARK!

AudiCoupeGT1986

Sorry, I didn't reply because I was stumped. I had assumed that you had figured out the timing before hand. Good job on finding out the solution!

Audicoupe4G

So, with your timing set correctly, did the rough idle go back to normal and is the car running properly again?

TEF1701

The rough idle absolutely went away, and the acceleration is extremely smooth. It still has a very minor hiccup while idling, but it's like night and day. The lurching and hesitation while driving is gone too. I don't know how the thing stayed running with the timing that far off. I'm mad at myself for missing such a stupid little thing, but at the same time I'm thrilled that I can finally start fine tuning the car. What's funny is I completely missed the page in my Bentley manual that shows the two marks on the flywheel. It was there the whole time and I missed it.

Audicoupe4G

Glad to hear that you got it working to your liking again.

BTW, was the timing retarded or advanced? Would think it was the former, otherwise you would have noticed the pre-ignition.

TEF1701

The whole retarded/advanced thing always confuses me. It was around 30 degrees advanced (btdc). Assuming that the the mark on the flywheel is around 15 degrees btdc, and my timing light advance was set to 15 degrees, that means it's been running 30 degrees advanced.

Audicoupe4G

Let us know what you do to get it running the way you want it to.

Bob