VIP161

iTrader: (3)

The vehicle is a 98' GS300 with about 145k miles. The codes are P0300, P0301, and P0304. The parts replaced so far are as follows:

All coil packs (OEM Denso)
All spark plugs (OEM Denso)
All plug wires (OEM Lexus)
Air filter (OEM)
MAF sensor (OEM Lexus)
O2 sensors (OEM Denso)

All vacuum hoses were inspected and the dried cracked ones were replaced. The stock intake does not have any cracks or damage. The timing is legit on the scanner. The car only misfires under load between the 2500-3500rpm range. Any thoughts?

jdiron29

You have a cyl 1 and 4 misfire, try swapping wires with a good cylinder and see if the misfire moves, you can do the same with coil.

VIP161

iTrader: (3)

I tried that yesterday. I cleared the codes then took it for a spin. I had the same results with the same codes.

jdiron29

Have you swapped spark plugs? If you have, the next step would be a leak down test to see if you have a bad/bent valve. There could also be a head gasket problem.

VIP161

iTrader: (3)

I'm taking the car in tomorrow so I can move the spark plugs around. I also had a leak down test in mind. I'll tackle those two and post the results.

VIP161

iTrader: (3)

Quick update. I removed my intake snorkel and the misfire went away. It was pressed firmly between the hood and the radiator. The radiator I have is a big Driftmotion all aluminum race radiator for an MK4 Supra. I've heard stories of those things running way hot. I think the radiator might have heated the air going into the intake causing a misfire. I could be wrong. But no more misfire.