I recently had the first smog check performed on my '05 2.5T. While waiting, I noted they were revving the car up pretty high as part of the test and wondered to myself if my 8 year old car (with 130k mi) will break after all that exercise it was getting during the smog check. Sure enough...

2 days later, I'm driving to work, and the engine starts chugging (not badly, but rough) and the CEL light briefly flashes. I let off the gas and pull over. Check under the hood, it has a rough idle. I turned back to head home (2 miles). The engine still chugging slightly all the way back, some sort of misfiring, nothing violent, just a very rough purr under acceleration, and low in power for sure.

While CEL light briefly flashed when it first happened, it never went back on.

I sit here wondering if the stress from the high revving at the smog check 2 days ago helped speed up a problem that was likely to occur anyway, and why I have no CEL light despite obvious misfiring.

I've ordered some new spark plugs, BOSCH FR7DPP+, which will cost me less than half what I will spend ordering the plugs from the dealer ($80+).

At this point I'm worried that if the spark plug change doesn't fix the problem perhaps it could be the ignition coils, which, after some research, I will probably go with THESE IDP Ignition Coils.

My problem then, is that if I have no CEL on, how do I know which coil could be bad? Replacing all coils at $50+ each is out of my budget right now.

Any suggestion is most appreciated. Thank you.

 

Get the codes checked. You can pull up each coil while running to see if you hear it arc to the plug. Or swap the coil from the misfiring cylinder to another, clear the codes, and drive. Check codes when it comes back to see if the code moved to the new cylinder.

 

Thanks for the reply ES6T, I didn't have to check which was the bad plug/coil as it became obvious while fixing it.

After watching a how-to video on YouTube, I was pretty confident I could do it myself so I went ahead and started the process with the spark plugs I got from the local O'Reilly store (BOSCH FR7DPP+). Total cost for the plugs: $30 (versus $80+ from the dealer). The plugs are nearly identical to the ones I pulled from the car.

I found the culprit in #4, as I pulling the ignition coils out, I notice it was very brown (versus Black for all the others), the rubber boot was torn and the spark plug there was completely shot. See pic below:



After a little bit of research and not wanting to wait many days to order through the net for the IDP Ignition Coils I wanted, I ended up purchasing the ignition coil from Pep Boys, which had 1 in stock for $56 (compared to $125 from the dealer). It is BWD brand part# E371. I was initially skeptical, but I saw many reviews on it from Volvo owners who were quite pleased with it, and in fact some had received the part with the VOLVO logo, presumed to be an actual OEM part. At the store, I inspected the part and it looked very identical to the OEM one. See the reviews HERE. I took the risk and purchased it.

After installing that new ignition coil and a set of new plugs, and test driving it a few miles, the engine is back to running very smoothly now, and in fact feels better than before the misfire. The engine feels much more responsive and rich in power.

My misfiring problem appears to be solved for under $100 (compared to $400 for dealer), and hopefully stays that way for a long time.

The whole thing took me over 2 hours start to finish with clean up (not including the trip to the store), but next time I can complete this in 30-40min tops.

The CEL light which eventually turned on, remains on after the repair, I read somewhere that it disappears after some use, which I am hoping it does.

.

 

Glad you got it fixed.

Comparing aftermarket prices to dealer prices will always give you the same result. Dealer parts always cost more. And doing it yourself will always be cheaper than the dealer.

 

If your CEL light has not gone off by now, go back to PEP boys or the nearest auto-parts place and ask them to borrow an OBD scanner (typically free, if not go to another auto-parts place). Use the scanner to read the codes again and copy them down on paper for future reference in case you run into a different issue that you need to troubleshoot. Then erase the code using the same scanner. Now your CEL light should be gone.

 

I had the same issue with my car at 150k miles, I replaced a couple of the coils and then a few thousand miles later the same thing happens. This time I replace all the coils and the plugs. that was 59,000 miles , still going strong. the bottom line is the coils should be replaced at 150k miles to keep things running smoothly. Replace them once and your are golden.

 

thanks for the response miki425 and volvoloverinthe505

UPDATE: the CE light went back to off on the 3rd day after the repair. Now almost 2 weeks following the repair, the car is running very good, and am quite happy with the new plugs, ignition coil and the fact that I can identify and know how to solve the problem now. Since it already has already 136k mi, I'll be ready to change the coils that will probably need replacing soon enough.