Sorry to post this here, but the responses on Audiworld weren't that great and this is the 'other car'.

I recently changed from Bosch F7LTCR to NGK BKUR6ET plugs on our 98.5 1.8T A4 (Wett 1 bar chip).

Test drive a few seconds later and it runs great. The next day, idle is rough after cold start for a few seconds (stalled once), but runs fine afterwards. This continues for the next two days, then it won't start after resting for 2 hours. Left it overnight and it starts the next day without much cranking, but runs a little rough and stalls once.

Pull over and change the plugs back to Bosch F7LTCR and it seems to run fine now! I am convinced that it must be the plugs, but I have a hard time imagining why it would be that different with NGK OE plugs for this engine. These plugs come installed by Audi in some cases, so I see no reason why they would be problematic.

These are three pronged plugs, which I did not think needed gapping, so I used them right from the box. However, some on the list recommend reducing the stock gap for chipped cars running ~1bar boost (like ours). If this is the case, how can one possibly properly gap a tri-pronged plug? It seems that the electrode to ground space is a curve, which would not allow for using standard feeler gauges and would be difficult to measure consistently.

Does this seem reasonable? It has to be the plugs, somehow. Also the CEL came on but went off after a few starts with the Bosch F7LTCR in there.

Thanks,

Ted
98 M3/4
98 A4 1.8T

Well I dont know much about plugs, but you need a special tool to adjust the gap. I just popped in my NGK and everything is fine :az:

Are those plugs copper or plat? Turbos hate plat as a basic rule of thumb. In my S4 I had the best results with irridum or copper. Also did you change the heat range?

Are you sure the heat range between the two plugs were the same. I know NGK and Bosch use a different numbering system ... I'm pretty sure they are inverse to each other ...

I'm pretty sure NGK's come pre-gapped ... but, are you sure they were gapped correctly?

I have no idea they made a 3 pronged plug, I thought it was either single tip or dual prongs. That's interesting. No idea how you would reduce the gap on that one then.

Wait a minute --- didn't Audi's have problems with their coil packs in that year as well????

Are you positive that it's the plugs ... I know you run better now with the plugs changed out again; but, any possibility that the coil packs were not secure on there before?

It's not the plugs, we had the same trouble arise a few days after returning the original (old) Bosch. Took it to the dealer and they said they needed to replace the coolant temp sensor (which explains why cold start=ok, hot start=problem) and fuel pressure regulator. They also said that the throttle body won't adapt to 'zero' position. They claim that this would not be affected by the chip. We're going to leave the TB in and take a look at it at another time if it runs ok. Maybe it only needs a cleaning?