Hello,

I just installed Bosch Platinum +2 spark plugs in my 1996 Volvo 960. After installation I turned on the engine and it has a rough idle. Soon the Check Engine light came on, so I turned the car off.
These plugs are what Auto Zone recommended that I purchase. I made sure to do each plug one at a time so that I didn't get the wiring mixed up. I tightened them with a torque wrench to 20 ft-lbs.

What can I do about the rough idle? I'm afraid to drive the car because I don't want to damage the engine. Should I just put the old plugs back in, or would that be a waste of time? Is it maybe running on only 5 cylinders?

are they gapped correctly?

The Bosch +2 Platinum plugs say they are factory gapped and not to change the gap.

This morning before driving it I double checked that the wiring was making a good connection to each ignition coil. It ran fine after that with no problems. However the service engine light remained on.

I took it to an auto store today and they hooked up the ODBII computer. It was a misfire on cylinder 2. The guy said to drive it for about 50-100 miles and that the service engine light would go off if there were no more problems (takes a while for the computer to reset that warning).

David

Sounds like he is just trying to sound like he knows what he is talking about.

Yes, most Bosch spark plugs come labeled as pre-gapped...however, always verify this. Many cars use the same plugs, and many have different gaps. Keep in mind these gaps are set in bulk and are usually just set to a certain amount of error. So, generally pre-gapped just means they are close to right but not exactly guranteed.

I have read in other places (cant say this is actually true or not) but the 850s are picky about spark plugs and the gaps. Your Bosch plugs spark hotter than standard OEM ones and the car may have some means of sensing this.

Still, first thing I would do is verify the gap is correct as Greek mentioned.

Second, verify that each one is actually sparking. Is it just a rough idle or might it be a fouled plug not sparking? Usually you can tell, but if you are not familiar pull them and check...the spark is obvious.

On the picky part again. I think I had read somewhere not to use platinums in an 850. Personally that is the plug I have used in every car I have had, but I havent replaced the ones in my 850 yet, so they are still whatever was there when I bought it.

On a side note, Bosch is pretty much AutoZone's top spark plug brand, and as such it is what they are going to suggest first (and oddly enough they tend to cost more than most the others...haha, imagine that). Just like with any such type of salesman they have certain brands they want to push more than others, and in their industry they are not there to supply the best OEM replacements, they are there to supply replacement parts that work, not necessarily work perfectly for your situation.

How do I verify the gap on a Platinum +2? there are two grounds that come down Here's a link to a picture.

I pulled out Bosch "Super" plugs, which look like a more traditional spark plug. I wish I had just replaced it with exactly the same thing I took out, but I didn't bother to look before I purchased the Platinum +2.

The rough idle has gone away--and it was bad--like it made the whole car shake and when looking in the engine bay the engine was shaking back and forth. THat went away when I double checked all the wiring to the ignition coils. Think the auto store would take these back as a return (even though they've been used for a day now), and let me exchange them for a less expensive, less complicated traditional plug like I pulled out?


(IMG:http://www.aboveallmotorwerks.com/prodpics/BOSCH_4301.jpg)