Little rough idle 2.9 i6

Post by **CIK7** » 01 Mar 2021, 07:07

This is for my straight 6 but was given permission to post here because the 6 is very similar to the 5.

So I have difficulty with a rough idle. Its been getting worse. Yesterday starting the car for first time of the day, it held up at about 1900 rpm for about 3 seconds and very quickly dropped to 900 rpm which is unusual. About a week ago, I was leaving my parents place, I started my car. The rpms went from about 1400, dropped to 400, back up to 1100, finally settled down at 750 (normal). When it sits idling, the needle constantly is moving down from 600/650-750. When I shift from an idle gear into a drive gear (vice versa) after sitting at least 30 sec, rpm sometimes drop to 400-600 before coming back up to 750 and resuming the needle dance. In this video, the idle is not as bad as it is now. The best part is at 51sec.

Post by **Ocelot** » 01 Mar 2021, 11:23

Yeah, these kinds of cartrouble are a bit hard to solve because there are a variety of reasons why an engine has a rough idle.

Did you check:
* The battery?
* The spark plugs? (maybe they're worn out or incorrectly gapped)
* The airfilter?
* Vacuum lines?
* Fuel injectors? (maybe they're partially blocked/dirty)
* Did you check if there are any faults stored in the EMS?
* Maybe you have the tools to do a compression test. What are the results if you do so?

I hope this helps a bit!

Post by **wizechatmgr** » 02 Mar 2021, 17:21

Sounds like something wrong with a crank bearing or wrist pin to me. Odds are you're going to want to drop that oil pan and check everything before you bother doing anything else.

Post by **CIK7** » 03 Mar 2021, 16:26

INSANITY! I just got back from NAPA where I had them scan my car for codes. INSANITY! I am only getting good firing on 2 cylinders. Also a critical misfire and engine coolant electrical. Latter is coolant sensor right? What about the others? What are y'alls opinion on Autolite spark plugs? Garbage? That's what I replaced the old plugs with back in 8/2020. I took a pic of spark plugs as well #6 (back) to #2 (front). See pics below...

Post by **abscate** » 03 Mar 2021, 18:12

Gaps look really big. I think spec is 0,7 mm / 0.028 thousandths

Post by **CIK7** » 03 Mar 2021, 18:26

abscate wrote: 03 Mar 2021, 18:12 Gaps look really big. I think spec is 0,7 mm / 0.028 thousandths

So the misfires are likely from excessive gap? Anything else?

Post by **scot850** » 03 Mar 2021, 21:27

I think this might be an iterative process. I don't know anything about Autolite spark plugs but certainly the older motors typically don't like alternative plugs. I believe others have had some luck with NKG equivalents and that is about it. I'd try setting the plugs to the correct gap. I'd research that the 0.028" is correct for your engine as I have no clue.

While you have the plugs out it is worth checking the condition of the individual coil packs and their boots to make sure you are getting a good spark. There is not anyway to really check them that I have read, but remove the boots from the coils and look for cracks in the bodies. Cracks don't always condemn them but compare the bad cylinders with the error codes. I typically find the coils seem to develop a single crack on the side opposite the cable plug in. and down toward the shaft of the coil. Also check the condition of the boots for splits or cracks which can allow the coils to ground.

As the plugs have a decent color, I'm not sure if they are the issue. But lets try the process of elimination.

AS for the temp sensor, not sure where it is on your motor, but you may find it has a bad or corroded connector. Start by cleaning that first. Then it will be a case of checking the sensor resistance verses ambient temperature. There will be a resistance chart somewhere.

Neil.

Post by **CIK7** » 03 Mar 2021, 21:34

scot850 wrote: 03 Mar 2021, 21:27 I think this might be an iterative process. I don't know anything about Autolite spark plugs but certainly the older motors typically don't like alternative plugs. I believe others have had some luck with NKG equivalents and that is about it. I'd try setting the plugs to the correct gap. I'd research that the 0.028" is correct for your engine as I have no clue.

While you have the plugs out it is worth checking the condition of the individual coil packs and their boots to make sure you are getting a good spark. There is not anyway to really check them that I have read, but remove the boots from the coils and look for cracks in the bodies. Cracks don't always condemn them but compare the bad cylinders with the error codes. I typically find the coils seem to develop a single crack on the side opposite the cable plug in. and down toward the shaft of the coil. Also check the condition of the boots for splits or cracks which can allow the coils to ground.

As the plugs have a decent color, I'm not sure if they are the issue. But lets try the process of elimination.

AS for the temp sensor, not sure where it is on your motor, but you may find it has a bad or corroded connector. Start by cleaning that first. Then it will be a case of checking the sensor resistance verses ambient temperature. There will be a resistance chart somewhere.

Neil.

The 960 2.9 is based on the p80 2.4. Just 1 extra cylinder. I will remove the coolant temp sensor from my junk car and put that one on to see if that helps.
The coils look to be in fairly new condition. I didnt see an issue with them. I'm gonna check records if they were done before my purchase.

Post by **CIK7** » 04 Mar 2021, 09:23

abscate wrote: 03 Mar 2021, 18:12 Gaps look really big. I think spec is 0,7 mm / 0.028 thousandths

Holy cheese! Were you correct!!! I bought the gap tool, gapped the Autolite Platinums that ive used over 6,000 miles between my XC and this 960. INSANITY! Yes Scot is correct its suppose to be .028 because the 2.9 technically based on the 2.4 and by golly the actual gap was between .042 and .047. Insane!
About a year ago I bought brand new Bosch fr7dc+ 7955 (which is same size all round as sp for p80) nickel copper plugs and did not use them. Bosch states they are .037, actually .035, and I adjusted them to .028. Put them in, NO CODES AT ALL. It seems to be running correctly now.

Post by **abscate** » 04 Mar 2021, 10:32

Wha duar meddle wi me

Heres a hint for the Scot in everyone...

If you order the set of 5 Volvo plugs for an NA car it is 8642661

If you order the same set for a 960 its 8642660 - but you get an extra plug.