Last Updated: 09/08/2025 @ 05:58 am

Community Member Credit: mydecember1985

Our ’02 bone-stock I35 w/113k on the clock had a weird burnt smell yesterday. I got it to the side of the road to look things over, but the smell wasn’t super strong. I googled it and was unaware the motor mounts were an issue with the VQ35s as well. I immediately disconnected them and drove it home. This car has no IACV, so I didn’t bother looping it out of the system today.

I just pulled the ECU and got these pictures. This ECU has “FQ” on top. The part number looks to be A56-T69 ZP8. NOTE: The bottom seems completely fine except for a minor spot around the 5th pin in that chip. No tracers on the bottom are burnt/black. Just that one on top that runs under those green chips.

The car seems to run perfectly fine except for some slight hesitation/surging that I think is more related to 1 non-OEM coil I had to swap in a few months ago and then forgot to track down a matching set of 6. (Wife’s car and is barely driven)

Does anyone know what system this chip is responsible for? Is it OK to continue driving if this thing just controls the motor mounts?

The weird thing is that there are NO CODES?!?!

Member Reference Notes:

• Fried time to replace the ST509
• Drive it. Get a spare ECU on order for $40 bux on ebay or go pull one at a yard for $25. NDSII to program keys.
• The ST509s controls engine mounts, VIAS, fuel pump, and probably the EVAP valves. The non-burnt ones control the fuel injectors. There aren’t any diagnostics for engine mounts, so you won’t get a code.
• Just do what has been suggested and get a replacement ECU. Cut the plug ends off the motor mounts so nobody does you a “favor” in the future.
• Your motor mounts (or wires to them) are fried. Leave them unplugged and keep chugging along. Hell even replace them with some aftermarket mounts. There’s 0 need to have electronic mounts in a vehicle this old.

So the ECU made it to Foreign ECU repair yesterday. They repaired it and are sending it back soon. They recommend I replace the IACV, but our car doesn’t have an IACV. See picture. It’s all one big piece of the throttle body. Is this part known to cause ECU failures? The motor mounts are still unplugged. Anything else I should replace?

Final update:

Replaced Throttle body to be safe. Motor mounts are left unplugged. Went to start car to get it warm and complete relearn. Car ran like absolute hot garbage! I was freaking out. The exhaust was smoking a bit (never has before) and stunk of unburnt fuel. I couldn’t even get it to maintain an idle long enough to warm it up and do the relearn. If I did keep revving it to warm it up, I was worried the insane amount of fuel dumping into the system was going to ruin the car’s already-fragile cats.

Since MAF has a lot to do with A/F ratio, I went to grab a Duralast replacement. The closest Denso/Hitachi was 4 hours round trip. $110 and it fixed the rich condition. I was able to warm the engine and relearn idle. Total cost: $250 ECU fix, $130 throttle body, $110 MAF. $490 total I’m really wondering if the MAF was the whole problem with the hesitation and the ECU was completely unaffected because it drove fine for a while the ECU burned up back in February-ish and I unplugged the mounts. I also have a spare throttle body now since it was doubtful that caused the failure.