Misfire ONLY at idle?

Cory · Post by **Cory** » 20 May 2010, 15:23

Hello,
I know I am new to joining this forum but for the last month I have been surfing it non-stop and have found GREAT info here that has really helped me do the maintenance to my 1998 S70. I appreciate everyone's input and you guys have really saved me from some headaches! I had been searching for a 1998-2000 Volvo for about 2 months before finding one. (I even drove about 4 hours to look at a 1999 XC70 but the salesmen tried to screw me so I had to walk out over $70 based on principal alone. Haha)

So heres the issue I am having:
I bought a 1998 Volvo s70 N/A (160k miles) about a month ago, which I was able to get fairly cheap due to the idle issue, and these are the repairs I have performed to try to solve it:
1. New wires, spark plugs, rotor, distributor cap (all Bosch, Bougicord, and Volvo purchased from FCP Groton)
2. Removed throttle body and cleaned it thoroughly, replaced gasket
3. Removed MAF and cleaned it with approved MAF cleaner
4. Replaced upper engine mount yesterday (such a pain without proper pressing tool, had to make one which frequently broke)
5. Ran Seafoam "water-torture treatment" through it before changing plugs, wires, etc.
6. Removed flame trap and cleaned all adjoining lines

I also checked the timing belt as a precaution. I also bought a new accessory belt, front (timing side) engine mount, and Bosch fuel filter (all of which I have yet to install).

Here are the symptoms:
The vehicle runs great once I start going down the road, prolly at like 5-7 mph, and the misfire is no longer present. I am getting the Random Misfire code, Misfire Cyl 3, Misfire Cyl 1 codes also. There is a little jerking action (im thinking misfire) at around 41-44 mph also. The misfire seems to be only occurring at idle. Also when I pulled the #1 spark plug it was black and smelled very strongly of gas. I am thinking it may be drowning at idle (like the injector is stuck?) and causing the misfire.

I am not new to working on cars, you name it and I have probably done it to a car. I like working on my cars but this issue is frustrating me, there doesnt seem to be anything on the forums that directly relates to what I am experiencing. Any advice or suggestions are greatly appreciated!!! Thank you!

---Cory

Post by **jblackburn** » 20 May 2010, 18:26

Ok, first of all, welcome to the site!

I think you may have already found your problem! Pull out the injector rail...unscrew the 2 bolts at the end, and then pull them lightly straight up. Hold the fuel rail over a bucket or shallow pan, or 5 cups/jars will work too. Then have someone crank the engine over for you and watch that injector. It should be pulsing like the rest of them, not just a continuous spray.

The other thing I might suspect would be a crankshaft sensor, sometimes they start to do weird things with age.

Cory · Post by **Cory** » 20 May 2010, 22:49

Thank you jablackburn!
Its good to hear that I am not the only one suspecting that an injector may be the issue! I will check it out tomorrow and report back on the results.

Is there a way to test the crankshaft position sensor? (a bit of a misnomer I think since it is actually located on the camshaft, correct? Or at least according to this diagram it is: www.matthewsvolvosite.com/forums/viewtopic.php?f=1&t=24969&p=106888 )
Is there a certain resistance or reading I should get?

Thanks again for your help so far!

---Cory

Post by **jblackburn** » 20 May 2010, 22:57

There are 2, a camshaft sensor AND a crankshaft sensor. I would start with the crankshaft. You should get a resistance reading of >200 ohms with the ignition off, or cranking the motor over you should see it fluctuate, but not drop below that.

Intermittent signals from the sensors can be hard to track down, however. It's just a theory though, I would definitely start with the injectors first.

Cory · Post by **Cory** » 20 May 2010, 23:08

I will do that!
So I should check the RPM (crankshaft) sensor (if the injector theory fails) and not the camshaft sensor?
Oh just a side note, when the car is at idle and misfiring, the RPM gauge does not fluctuate. It stays at a steady 850-900, which I think is strangely high. What should the idle be at? And obviously this is when it is at normal operating temp.

Post by **jblackburn** » 20 May 2010, 23:16

That's where I would go. The camshaft sensor will USUALLY throw a code if it's mad; the RPM sensor won't always.

The camshaft one can be checked as well, if you want to, but testing isn't as definitive on it. You should see <5V from Pin 1 (front of car) to pin 3, and 12V from 2 to 3, and 3 should ohm out 0 to ground. I might have mixed up the voltages on the pins there, but you get the idea

That's normal for these engines, it is right where it's supposed to be...the 5-cylinder is a bit of a weirdly balanced configuration, and if the idle drops lower, it gets rough. Seems kinda weird with some 4- and 6-cylinders today idling around 500-600 RPM.

Cory · Post by **Cory** » 20 May 2010, 23:36

Ok good! I thought it was idling waaay too high and was worried sick about it. I guess I am just used to my Honda which idles at like 600. Haha. And my 740 idles at like 700 so I figured all Volvos should be in the same range. You learn something new everyday, right?

Cory · Post by **Cory** » 24 May 2010, 17:13

UPDATE:

Ok so I finally got around to working on the S70 today but before that I took a trip to the junkyard. Good thing! I pulled an injector off of another N/A S70 at the junkyard and went home to start working on mine. I first changed the fuel filter, easy fix. Then I figured since the fuel pressure is gone I might as well check the #1 cylinder injector (since that was the one we determined to be running too rich and/or drowning the cylinder causing the misfire at idle). As soon as I got the fuel rail loose I realized that the #1 injector was RED. Not yellow/orange like the others and the one i pulled from the junkyard. That was a bit of a surprise. So I changed it out and the car is running slightly smoother but still not 100%.

Any other suggestions?

It could be that it just needs to be driven around a little bit or maybe a battery disconnect?? I havent done that yet. I usually just check and clear all the codes. Will that do the same thing or does the thing need to be reset basically? So that it can re-learn the new injector and fuel mapping.

It is throwing a CEL but I havent checked the code yet. (Finally returned my borrowed Scantool to Autozone, Ive had it for a month!)

I really would appreciate any suggestions as to the next step I should take. Thank you!

---Cory

Post by **jblackburn** » 24 May 2010, 18:25

A full reset (battery cable) will let it re-learn, and then if you have any more codes show up, then you can read them.

What color are your other injectors?

Orange/brown are 315cc. Red/white is 350.

I don't know why there are so many colors.

Cory · Post by **Cory** » 24 May 2010, 18:34

The other ones are orange/yellow. The one on the #1 cyl. was bright red...totally different from the other ones. I have no idea how or why it was put on there but at least they are all matching now. Any ideas where the red one might have come from? If I remember correctly it did have Volvo on it.

Ok thanks jablackburn! I will try the battery reset soon. I need to find/get the radio code though. Any chance I can call a stealership, read off the vin, and have them tell me the code? Im thinking no...but maybe someone has had some luck with that.

Thanks again!

---Cory