2003 V70 Non-Turbo Rough Idle; hesitation on acceleration

jtklein · Post by **jtklein** » 11 Mar 2015, 10:38

Hello,

I have an 2003 V70 non turbo automatic with 259k miles. All of a sudden, the car started to idle rough and hesitate on acceleration. When I turn the AC off, it runs better... not great but better. It seems like a misfire. I took it to Autozone and it's throwing P0300 and P0420, basically no help as they say there are an number of things that it could be from a misfire to vacuum leak to catalytic converter to O2 sensor and more. About 2 months ago I replaced the crankcase ventilation box, and all seems to be well with that. At that time, I also replaced the #3 coil pack and plug as it was oil fouled. Disconnecting each coil pack at idle, each one makes the car run even more rough, I may be wrong in my thinking, but this seems to eliminate a misfire from the plugs. I replaced the O2 sensor 2 years and 72k miles ago. Cleaned the air filter and MAF and no change. No noticeable loose hoses for a vacuum leak. Any ideas what it may be?

Post by **chrism** » 11 Mar 2015, 11:19

P0300 is a random misfire (likely not just a single cylinder).
P0420 is a fault related to catalytic converter efficiency.

One of these may be the cause and the other an effect. The problem is it could probably work either way.

Rough idling that seems to clear up when you are accelerating or running at higher RPMs is often caused by a sizable vacuum leak.

"...About 2 months ago I replaced the crankcase ventilation box..."

I'm guessing when you replaced the ventilation box that you had the intake manifold off??? If so, did you use a new gasket upon reassembly? Get all the bolts tight? Even the one that's partially hidden by the thermostat housing?

draser · Post by **draser** » 11 Mar 2015, 11:28

Is #3 plug fouled back again?

jtklein · Post by **jtklein** » 11 Mar 2015, 11:50

Thank you for your response. When I replaced the manifold, I did replace the gasket. I torqued down the bolts to the specified amount, but I too thought maybe one might be loose. I'll see if I can get to it tonight and check for loosening.

I also replaced the #3 spark plug, though it did look ok.

So for a random misfire, is it then reasonable to replace all spark plugs?

Post by **chrism** » 11 Mar 2015, 12:14

"...So for a random misfire, is it then reasonable to replace all spark plugs?..."

Why not?

Normally I don't like to start swapping parts to cure a problem, but in this case you can purchase the sparks for about $2.50 ea. = $12.50 total.

What kind of plugs are in there now?

Post by **oragex** » 11 Mar 2015, 15:06

I'm trying to see what's related with the A/C helping smoothing things.. but it's not easy

I does sound like a severe misfire. Could be as easy as a coil plug, a faulty spark plug, cylinder compression, faulty injector/injector seal (perhaps a broken seal when the injector rail was put back? - the seals need some vaseline on them to slide back smoothly), a leak at the fuel rail gas line?. I had these exact symptoms when I messed up an injector, but of course it's not the only possible reason. The catalytic code is surely related to the misfire (the convertor can't burn all residues because of insufficient combustion in one cylinder so the downstream O2 sensor triggers the code)

jtklein · Post by **jtklein** » 11 Mar 2015, 15:34

Thank you both. Right now, they are Autolite double platinum.. about $4-5 per @ Advanced or AZ, still reasonably cheap to do and possibly one way of eliminating at least one possible issue. I'll try that and if it doesn't fix it, I may get another coil pack and swap out one-by-one. I'll look for vacuum leaks and check the bolts on the intake.

Oragex, yes, the fuel rail was a little tricky.. not so much getting it on as taking it off, but if it was that, wouldn't the issues have presented itself sooner? I did this the week between Christmas & New Years.

The catalytic converter probably needs to be replaced as it is original. Here's something that has perplexed me; back 25-30 years ago, the converters were considered power robbers and people would replace them with a straight pipe. I never see a mention of that anymore. Should they actually be replaced or can they in effect be bypassed like the old days?

draser · Post by **draser** » 11 Mar 2015, 17:25

You stated you replaced #3 coil and plug which was fouled, then you said you replaced it but it looked ok? Reason for the question is if there's a pattern of plug 3 getting fouled that may be the cause for misfire. The thing with the A/C is that when on idle goes up so more fuel gets in. If it runs rougher it's because it may be already running rich so with even more fuel when A/C is on now ignition can't keep up. If you have a scanner you could get freeze frame data related to your faults and live data that will tell what the deal really is.

jtklein · Post by **jtklein** » 11 Mar 2015, 21:03

Well problem solved.. or at least mostly. It is still running a little rough, but not bad at all, just not quit how I would like it. I disconnected the neg terminal, changed all the spark plugs to new double platinum, checked the bolts on the intake and they were fine, but I also checked the clamp to the hose from the crank oil vent tank and it needed tightening. That being loose may have cause a vacuum leak, but I don't know. Anyway, when I put it all together, it started right up and ran smooth with good acceleration. The plugs I removed actually looked pretty good with #5 looking a little rich.

Thank you Draser. I had changed the #3 because there is a hose from the crank oil vent tank that is between #3 & 2 and when the tank was bad, it was blowing oil all around there and there was oil pooled on top of the coil on #3. I change it again just out of precaution but wasn't really necessary. I do need to get a scanner or something for better diagnosis. What would you recommend?

draser · Post by **draser** » 12 Mar 2015, 06:22

Glad to hear it's sorted. I'm using, with good results so far, the Torque Pro app installed on my phone ($5.00) paired with a OBD2 blue tooth adapter ($25.00). It gives access to a lot of live data which makes diagnostics easier and saves money in the end. There's also Vida Dice, which a lot of members have, it has way better capabilities I understand, price's not bad and members seem to like it.