: Rough Idle



ivanawfulitch
10-13-04, 08:46 PM
My 2001 STS with 36,000 seems to idle slightly rough. Is this normal with the Northstar? Also, what can I do to keep my Northstar running for the long term? I change the oil regurarly and keep an eye on the coolant level, but is there something else I should be doing? Thanks.



MJE
Cadzilla

Ranger
10-13-04, 09:52 PM
Rough idle is not normal.
As far a maintainence, just change the oil and coolant as required.

Mitch3
10-20-04, 02:00 PM
Found a lot of posts lately regarding rough idle. My 94 Eldo got so bad I started putting it in neutral when stopped at a light. After a tuneup and a bunch of other stuff, I found that a container of DriGas helped a little. I then started to change brands of gas. Tried Shell V-Power which I liked but my mileage went way down. I've now been using Sunoco Ultra and the car has been running great with around town mileage at 23.4. Try switching to different name brand gasolines with a container of DriGas. It might solve your problem. I'm really convinced that it has been so wet this year in almost every area of the country, some of that moisture is working its' way into our gas lines.

dkozloski
10-20-04, 03:08 PM
Some small amount of water is present in petroleum products as they leave the refinery. In some very cold climates this will freeze into ice crystals and cause all kinds of phantom problems. In a warm climate it doesn't take very much more additional water to create havoc. Most fuel storage leak detection systems monitor for water in the storage tanks but it is up to the station operator to have the water pumped when it becomes too much. If there is some water that has settled out in the bottom of the storage tank and the supply truck delivers some more product the water is stirred up and mixes with the gas. Now Joe Scooterberry customer comes along before it has a chance to settle, buys a tank full, and has problems. The station's filters are supposed to protect against this but there are a multitude of reasons why the filters are not 100% efficient. Fuel contamination has prompted a lot of tuneup work. A newspaper where I worked had a load of fuel delivered that was about 50% heating oil. There were stalled vehicles for miles around.

BeelzeBob
10-20-04, 03:16 PM
My 2001 STS with 36,000 seems to idle slightly rough. Is this normal with the Northstar? Also, what can I do to keep my Northstar running for the long term? I change the oil regurarly and keep an eye on the coolant level, but is there something else I should be doing? Thanks.



MJE
Cadzilla


Well....it depends on what you call "rough".....

Sevearl things to consider in the discussion:

The STS/SLS package from 1998 on (including your '01) is sensitive to engine idle quality/idle stability. The normal idle degradation with the 300 HP Northstar due to the more agressive cam timing (compared to the 275 HP engine) is much more evident in the 1998 and later STS/SLS than in the earlier cars. This is simply the "nature of the beast" with the revised engine mounting package adopted in 1998 in the new Seville which gives better road speed isolation but it is sensitive to idle instability.

The Northstar engine was redesigned significantly for the 2000 and later model year. Key to this discussion is the fact that the compression was lowered slightly to run on regular fuel along with the incorporation of a roller cam follower design valve train. The cam profile for the 300 HP engine is fairly agressive to make the 300 HP for the L37 engine in the STS. This naturally leads to a slight degradation in idle quality due to the "cam". The cams in the 2000/2001 engines are very aggressive to retain the 300 HP rating even with the change to regular fuel. This, unfortunately, lead to a number of idle "quality" complaints in the field. Enough that the cam profiles were modified in 2002 with slighlyt less duration and overlap. This causes a minimal loss of power and improves the idle quality significantly...reducing the "cam" effect at idle that you can feel.

The 2001 has the OBD2 diagnostics that include an onboard misfire detection system that is very good at detecting misfire. This was not the case on 1995 and earlier Northstar engines. A 95 or earlier engine could misfire and idle very rough and not necessarily set a code. A 96 or later will definitely set a code if a cylinder is misfiring.



Sooooo.....how rough is your idle....?????

If it is just a tremor that is felt in the steering wheel and toe pan/foot well and otherwise the engine is stable in idle and does not stall, etc.... I would tend to say that your idle is normal for that engine in that car for that year. The later edition cams will idle noticeably smoother albeit with a slight loss in power on the dyno. If you are not setting any check engine lights or setting any diagnostic codes then I would tend to think that the engine is fine. If it were missing at idle it would be very rough and it would set a misfire diagnostic code. It would NOT be just a steady tremor from the powertrain that is typical of a more agressive cam...not quite a lope from the cam but getting close.


So...you'll have to decide. I suspect that you are just feeling the high output cam in the 300 HP engine. Some people thought nothing of it as it just feels like a "big cam"....but other people did complain. There is a service kit containing the revised cams and a calibration for the PCM to go with it that is available at the dealer for retrofit if the idle is just umbearable to you.

The biggest problem with this was that people that run the engine hard and like the performance typically did not notice the idle...kind of what was expected of an STS. The owner that should have bought an SLS but got an STS to have the "best" car often drove the car more gingerly and complained about the idle.

BeelzeBob
10-20-04, 03:18 PM
The most important thing to do to keep the engine happy is to service the cooling system regularily, change the oil according to the oil life indicator and air the engine out occasionally. It likes a regular dose of WOT to keep the carbon cleaned out.

I_Need_a_Northstar
10-21-04, 01:34 PM
Hey read this. This is how you got you engine to not idle rough
Hey go to you nearest Caddy dealer and ask for coolant pills. There only like $3. Put them in your coolant and its kinda like tire slime. The Northstar engine is a cast aluminum engine it has tiny holes in the engine. It will miss like that. Even a new engine will. Put those Engine Coolant Pills in the collant you might have to crush them in there, then go drive it for a while and it wont idle rough anymore

JSMeloche
10-21-04, 03:16 PM
wtf.... now we have a junior member telling bbobynski what to do LOL

keep up the good work bbobynski!!!

Hey Bbob... so your saying that the 2001 engine has a very agressiv cam. If someone was to put a 2001 cam on a high compression N* (pre 2000) would it make more thant 300hp?
Might be interesting, i found a wrecked 2001 300 hp N* the other day, maybee i could swap the cam in my 95 STS hehehe and have a super N*

eldorado1
10-21-04, 03:36 PM
Hey Bbob... so your saying that the 2001 engine has a very agressiv cam. If someone was to put a 2001 cam on a high compression N* (pre 2000) would it make more thant 300hp?
Might be interesting, i found a wrecked 2001 300 hp N* the other day, maybee i could swap the cam in my 95 STS hehehe and have a super N*

I was thinking the same thing... great minds think alike? It would involve swapping the roller cam 2000+ heads onto a <99 block though.. And I kinda doubt it would be worth much more than 15hp. (What did the ratio go to? 10->9.0 or something?)

Ranger
10-21-04, 04:06 PM
Hey read this. This is how you got you engine to not idle rough
Hey go to you nearest Caddy dealer and ask for coolant pills. There only like $3. Put them in your coolant and its kinda like tire slime. The Northstar engine is a cast aluminum engine it has tiny holes in the engine. It will miss like that. Even a new engine will. Put those Engine Coolant Pills in the collant you might have to crush them in there, then go drive it for a while and it wont idle rough anymore
The coolant tabs are used as a precaution in case of casting porousity. They have NOTHING to do with idle quality.