My 1998 V70 Base model, started with a rattle in the Catalytic Convertor, then started a random miss. Now under load it misses and stutters. It is throwing the P0304 code for #4 cylinder miss fire. I pulled the plugs cleaned them, cleaned the cap and rotor. Looked for vacuum leaks. Moved spark plugs around. It is still doing the same thing. Idles good, but under load it misses and stutters. While running I pulled plug wires to make sure #4 cylinder is firing. Every plug wire I pulled made a difference in the RPMs. No obvious problems when I looked at the spark plugs. I have ordered a tune up kit from FCP. Can a clogged or partially clogged Catalytic convertor cause these symptom? I had thought I would get another OBD code, but all I get is p0304. It does sound like the cat has gotten worse. You can hear it rattle when you start and turn of the engine. I can't tell for certain if the exhaust flow is being restricted or not.

I am going to take it in to replace the catalytic convertor, but want to see if anyone has other ideas for the problems I am having.

 

Ok, I replaced the catalytic convertor. They did say that the cat was broken up in the center.

Was running good for about 15 minutes then started acting up again. Seems like it is missing under load and only gives the p0304 OBDII code for #4 cylinder misfire. Still awaiting the tune up kit. If anyone has seen this before, please let me know.

 

Still awaiting tune up kit, but worked on it some more. Cleaned throttle body intake. Found one breather to intake hose a little loose, tightened that up. Cleaned MAF sensor. Ran engine hoping it was the loose hose causing the problem, check engine light came on immediately, car ran great for about 10 minutes, started missing and sputtering. Checked the OBD again, got code P0102, Mass or Volume Air Flow Circuit Low Input. Cleaned the MAF Sensor with intake cleaner. Now I get P0304 code again, car still runs the same, runs bad after warm up, no longer see code P0102, but if I pull the connection to the MAF Sensor, it will run decently. Does that mean the MAF Sensor is bad, and causes the P0304 code? Any suggestions? Is that an accurate test for the MAF, (pull connection, and if car runs better replace the MAF)? I have not found anywhere that a bad MAF could cause a P0304 code.

 

Tune up kit arrived. Installed new spark plugs, rotor, cap, ignition wires. Soon after warm up starts missing and stalling. I am now only getting the p0102 code. Does this mean the Mass Airflow sensor is bad? If I disconnect it, it will idle.

 

Yep. Check the wires first to make sure it's not a simple short or frayed connection. Otherwise change that bad boy out.

 

I would agree. If that doesn't totally clear it up, I would also suggest doing a compression test. Heck, you might want to do that before doing anything else. You may have a bad valve causing the missing. Hope not but there is one way to find out.

Compression Test - Volvo S70 GLT, 1998

 

Thanks for the replies guys. I replaced the Mass Airflow Sensor, and now it is running good again. No more codes so far. Running nicely.

Recap:

P0304 - cleared by plugs, cap, rotor, wires.

P0102 - cleared by Mass Airflow Sensor.