99.5 1.8T (AEB) P0302 - bad ICM?
 

I have a 1999.5 A4 1.8T AEB engine with about 102K miles on it, chipped with a GIAC stage 1. For the most part, it's been running like a champ. :)

A few months ago I started to get an intermittent CEL P1136 (system too lean), which through research I determined was a vacuum leak. I used the "spray engine with carb cleaner" method but couldn't find anything and just ignored it, and she drove fine until 2 weeks ago when I started to miss badly, getting P0302 (misfire cyl 2).

This time when I popped the hood, I heard a loud hiss coming from the hose from the front of the intake manifold to the diverter valve. The rubber hose basically cracked at the nipple. I replaced it with some new silicone hoses, reset the codes, and took her out for a test drive. She drove great until I pushed it a bit with some WOT acceleration and after 10 minutes of spirited driving, P0302 came back. I double-checked the new hoses, they looked good, so now I'm thinking P0302 was unrelated... :confused:

Researching this code, I followed the recommended diagnosis:
1. Swapped coil packs cyl 1 and 2. No change.
2. Pulled spark plug from cyl 2, saw it was gapped a bit too big (.040). Regapped to .032 and swapped it with the plug in cyl 1. No change.

The plug from cyl 2 smelled of gas and was also much cooler than the working plug from cyl 1, so I'm thinking cyl 2 is not getting spark. Am I correct to assume that the ICM is probably bad?

Is there any noticeable difference in replacement ICM's? I see some on eBay for as low as $19 (seller: aa_auto_parts), one by URO parts on RockAuto for $39, and the OEM (?) ones on ECS Tuning for $116.

Thanks in advance for any responses!

You've basically narrowed it down to the ICM, yes. Congrats on following the right procedure.

The engine needs three things to run: compression, spark, and air/fuel. You've got air/fuel (smell of gas, wet cylinder), you didn't mention any catastrophic noises so we'll assume your compression is good, so the spark is what we're chasing. You've swapped coil packs and the misfire didn't follow them, so you're stuck replacing the ICM or deleting it and upgrading to 2.0T coil packs.

I can't pass judgement on the aftermarket brands as I've never used them, but this is the type of thing I tend to go for OEM replacements. Unfortunately they aren't cheap. When my ICM died a few weeks ago I got a used one from the junkyard for $15.

Thank you very much. Just wanted a voice of experience to confirm my assumptions.

I guess at $19 (vs. $116) the price difference is enough where it's worth the risk. Worst case is I'm out an extra $19.

Thanks again! :D

One side note, besides how awesome it was to see someone using their head and troubleshooting correctly...

With the chipped ECU, I would recommend gapping you spark plugs to .028.

Thank you brad for the complement and the advice. I'm going to regap now and see if there is any improvement.

I re-gapped everything to .028 and no change. Still shuddering and P0302... not really surprised, but I was still hoping ;)

I'll update again once I swap out the ICM.

New ICM Fixed it!
 

Got the new ICM from aa_auto_parts (eBay seller) in the mail today. I came with some thermal paste (?). I swapped it out in about 10 minutes (I thought working on Honda's was easy ;) ), unplugged the negative battery terminal for 30 minutes to make sure the ECU resets.

Started it up, cleared the CEL codes and the misfires went away! :D Took it for a spirited test drive and she drove like new.

Many thanks to bradtyler02 and BaseDrifter for the help and advice.

If this ICM goes bad, I'll be sure to update this thread... it will give others an idea of their quality. If you don't see an update, you can assume the eBay ICM is still working.

Great glad to hear it, keep us updated.

Just wanted to update everyone on the eBay ICM. I'm just under 105K miles now, and she's still running great.

wanted to update this thread. just passed 116K miles on the eBay ICM and still working great.