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Old 05-01-2010, 03:32 PM   #1
FredM
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2002 SL2
Default Rough idle in Drive, normal in Neutral

I was hoping the new fuel pump would have taken care of both the hard starting problem and this idle issue, but we only got half way there.

1997 SL1 with 107,000 miles.

1. New plugs and wires are not due yet, they were done around 100k.
2. New ECTS and connector done 2 years ago.
3. New fuel pump a couple of weeks ago ( starts first time, every time ).
4. New Wix fuel filter at 100k.
5. Bottle of Techron added to last tank of gas.
6. Throttle body cleaned last summer.
7. MPG is fine.
8. Motor mounts are recent.

Symptoms. Starts fine, runs fine. After warm-up, stopped at a light, idle will dip to around 650 and we get vibration. Put it in neutral and she goes right to 750rpm. It is consistent, this does not come and go.

EGR? IAC? Vacuum issue???

I'm lost. Any advise?

Thanks
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Old 05-01-2010, 03:43 PM   #2
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2002 SL1
Default Re: Rough idle in Drive, normal in Neutral

They're not the smoothest engines, the idle rpms seem similar to mine.
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Old 05-01-2010, 08:50 PM   #3
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2000 SW2
Default Re: Rough idle in Drive, normal in Neutral

I disagree. My 1996 SW2 with 189k idles smooth as silk. I can't even perceive that the engine is on when stopped at a light.

The fact that it idles rough in drive and not neutral means that it's probably the motor mounts. When in drive the engine/drive train are torquing against the brakes.

Perhaps you need to adjust your dogbones or replace the top motor mount (if you used the frowny face design).

I would also recommend running a bottle of seafoam through the air intake.
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Old 05-02-2010, 09:32 PM   #4
FredM
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2002 SL2
Default Re: Rough idle in Drive, normal in Neutral

I'm having a hard time making the connection between motor mounts and an idle dip. Can anyone shed light on how mounts could be the issue here?

For what it's worth, the mounts were replaced when we got the car two years ago, and we haven't put all that many miles on the car since then.
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Old 05-02-2010, 09:57 PM   #5
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1999 SW2
2002 SL1
Default Re: Rough idle in Drive, normal in Neutral

My '99 SL1 was doing this a few months ago. I changed the wires and IAC and it now runs smooth. Double check that when you have it in drive and it's running rough, have someone take a look at the plug wires near the coils to make sure there isn't sparking between two. I've done the IAC on two of my saturns though, one at 150k the other at around 140k, so it could very well be that.
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Old 05-13-2010, 10:00 AM   #6
FredM
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2002 SL2
Default Re: Rough idle in Drive, normal in Neutral

Update:

My son cleaned the throttle body and while he had it apart, noticed the o-ring on the IAC was a little shredded and wrapped around the shaft. He also noticed the PCV was pretty gunked-up, so he replaced the IAC and the PCV.

Things improved slightly, but we were still getting the idle-dip while stopped in Drive, so I started tampering with the idle-set screw on the throttle body and we're idling right at 700 in Drive and just avoiding the shudder. Need to tweak it a notch, I think.
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Old 05-13-2010, 10:31 AM   #7
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1999 SL2
Default Re: Rough idle in Drive, normal in Neutral

When the car is in drive (D), the engine is engaged with the transmission and wants to move forward but can't since you have the brakes on at say a red light. In other words, the engine is pushing forward trying to spin the transmission which eventually spins the tires. As the engine pushes, things that compress do compress such as the rubber cushion on your engine mount ... at the same time the force of the rubber cushion pushes back and eventually is successfully is pushing back the engine. This back and forth motion is the vibration and it occurs (taking a guess here) hundreds of time per second.


When you have the engine in neutral (N), then the engine is dis-engaged from the transmisison so there is no forward motion or pressure to move forward. This means no pressure on the engine mounts since the engine isn't trying to move forward so there should be less vibration. The little vibration felt during neutral (N) is from your engine spinning / combusting internal in a relatively balanced system.
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Old 10-03-2010, 06:38 PM   #8
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2001 SL2
Default Re: Rough idle in Drive, normal in Neutral

Quote:
Originally Posted by ShawnV View Post
I disagree. My 1996 SW2 with 189k idles smooth as silk. I can't even perceive that the engine is on when stopped at a light.
I had a 1995 SW2 with 100k that also ran as smooth as silk, too. I would still be driving that great little wagon if it hadn't been destroyed by a falling tree. I loved that car.

But my 2001 SL2 has vibrated in drive since the day I acquired it. I've had all new engine mounts installed, first aftermarket and then OEM. I've also loosened the engine strut mount bracket and retorqued it - three times, in different angles! No change. New wiring, new plugs, good compression test results, new serpentine belt, the works. This '01 STILL vibrates when stopped in drive.

I know many say that the engineering is all the same, but there's got to be something very different. I have spoken to two other owners of '01 SLs and they have the same vibration issue.

Personally, I'm giving up now after months of costly work in vain. I'll keep slipping it into neutral at stops until I've saved enough for an electric car.
...
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Old 10-03-2010, 08:24 PM   #9
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1995 SW2
Default Re: Rough idle in Drive, normal in Neutral

I have the same vibrations in my 95 SW2 with 124K on it. I just replaced the pcv valve, air filter, o2 sensor, vent tube, motor/trans and torque strut mount and it's still vibrating when warm in drive at idle. It was REALLY bad before, but now it's definately calmed down a ton after the mounts. I just chocked it up to how the engine runs. It runs very well but just vibrates.......
...
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Old 10-21-2015, 01:48 PM   #10
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Default Re: Rough idle in Drive, normal in Neutral

Quote:
Originally Posted by FredM View Post
Symptoms. Starts fine, runs fine. After warm-up, stopped at a light, idle will dip to around 650 and we get vibration. Put it in neutral and she goes right to 750rpm. It is consistent, this does not come and go.
Sorry to dredge up an old thread. This is what I'm seeing on our 96 SL1. Note: SL1 is not the same as SL2 in terms of idle smoothness IMO.

I'm wondering if this is something to do with one of the transmission solenoids? Possibly the TCC one. I checked it's resistance at the top of the pin connector and it reads 4.5. All the others read 5.

I don't believe it is anything related to engine mounts, and I didn't see anything solid that was cited as a solution.
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Old 10-21-2015, 02:53 PM   #11
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1998 SC2
Default Re: Rough idle in Drive, normal in Neutral

First you have to actually run a proper compression test to verify even compression. The below procedure will answer all the quwestions if performed as written.


To prevent washing the cylinders down with fuel remove the PCM B fuse to shut off the fuel pump, injectors, and ignition before starting the test. Remove all spark plugs and block the throttle open. Use a low charge rate battery charger to fully charge the battery before conducting the test.

Crank the engine until the gauge quits increasing and compare both the final pressure and number of compression strokes to reach the max pressure, cylinder to cylinder. You can do this test either cold or hot or warm just mention it when stating results.

For example if you find all cylinders produce a final reading of 200psi but the compression cycles are as follows: 1-8, 2-6, 3-8, 4-14 then it should be obvious that cylinder #4 has a serious problem with leakage past either the valves or compression rings.

FSM states the MINIMUM number of compression cycles is 10 and a Fully charged battery is required to obtain the full 250RPM cranking speed.

Nominal compression for a high mileage good condition DOHC is 190-220psi and SOHC will be about 10psi lower. What you are looking for is even numbers across all cylinders.
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Old 10-21-2015, 05:47 PM   #12
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Default Re: Rough idle in Drive, normal in Neutral

I understand what you're saying, but I'm not concerned about the 'roughness' of the SL1 engine. Maybe I should have been more specific. Here goes:

The car starts fine, warms up fine, gets terrific fuel economy etc. Once the car reaches operating temperature the idle will 'stumble'. By that I mean at stop, in drive, with foot on the brake the tach will show a 50-75 rpm drop and the car will shudder. This happens for only half a second and then the idle comes back up to around 650. This pattern repeats itself every 10-20 seconds. The problem only occurs when the car is in drive, not when it's shifted into neutral.

I know the compression of the 1.9 SOHC isn't all that great, especially since we've had a leak from the head gasket just behind the #1 cylinder for the past 15 years. (Car was bought new off the showroom floor).

This is a very low mileage SL1 with full load. The IAC has been replaced 2x and the EGR also due to frozen pintle. TB has been off and cleaned 2x in the past 3 years.

Overall the car has been relatively low maintenance till this year, but none of the mtce items except fuel filter relates to the engine. I don't know if the TPS could be also contributing to this 'surge' in idle? Of course it's only noticeable when stopped and in drive, as previously mentioned.

EDIT: the symptoms are exactly the same as the OP with his 97 SL1.
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Old 10-21-2015, 07:31 PM   #13
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1996 SL1
Default Re: Rough idle in Drive, normal in Neutral

I have a similar problem: The idle dips rhythmically in D. It stays at about 700. and then every 1 or 2 seconds it dips to 580. I had cleaned the throttle body and iac, and thought I solved it. It came back a few days later, but I noticed it only does it when the car was at a certain temperature: if I get off the freeway and drive around a few minutes, it will do it at stop light. I realized my thermostat wasn't letting the car get up to temperature (always hovering over 1/4 temp). I thought to myself when I get around to redoing the thermostat it'll all be fixed.

A couple weeks later, I decided to swap the t-stat, and much to my annoyance, now that the car fully warms up, it turns out this fully warmed up temperature IS the temperature range where my idle is dipping. The dip is load related: If I am idling in drive and everything is fine, turning on the lights or a/c blower, the engine will dip. I have a SL1, and those will bump up the engine rpm to conpensate for load. Sometimes it seems like it bumps it up too much, and then overcompensated to lower it, and the idle starts bouncing up and down rhythmically. Sometimes doing something simple light turning the lights off and on, or pushing the door lock button, will disturb the oscillation and it will stop, until I drive off and stop at the next traffic light. My car is very frustratingly at the edge of being stable. I will try re-cleaning the IAC... maybe I was too gentle with it last time, or just say eff-it and pick up a new one.

Good luck getting your car stable. Whenever you find what the problem part is, post it, and I'll check that out on my car immediately :-)
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Old 10-21-2015, 07:44 PM   #14
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1998 SC2
Default Re: Rough idle in Drive, normal in Neutral

Car is running lean, clean throttle body IAW this video. https://www.youtube.com/watch?v=Pc5qCuQLmFE

Check exhaust systems for leaks.

Exhaust leak check.
--Locate a low pressure high volume air source, reversible vacuum cleaner, large fan, leaf blower or what ever you can find.
--Loosely couple to cold exhaust at the tail pipe, or direct fan at tail pipe.
--Spray every inch of the exhaust between the head and CAT inlet with a mixture of 2 or 3 drops of dish soap and water in a spray bottle.
--Pay close attention to the lower flange, lower support clamp, and flex connector.
--The flex connector is under the protective braid so it requires quite a bit of solution to show any leaks.

Thermostat and ECTS have been mentioned, verify both are functioning correctly. Looking at the temp gauge does not verify proper operation.
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Old 10-22-2015, 01:10 AM   #15
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2001 SL2
Default Re: Rough idle in Drive, normal in Neutral

I tried everything suggested above, and my absolutely beautiful little 2001 SL2 still ran like a 2-cycle chainsaw on bad fuel, despite checking out okay at the mechanics in every way. They were baffled by its ragged performance (and this is a shop with 4 decades of an A+ rating).

I finally gave up in despair, when its A/C totally failed and posed prohibitive expense to fix, and the CD/cassette players quit working completely (the radio still worked, but nothing else). I sadly traded this gorgeous Saturn in for a 2007 V-6 Buick LaCrosse, which is so quiet and vibration-free that it truly does seem like it's not even running when it's stopped in drive - I have to look at the tach to make sure the engine's still running! And its sound system is better than my home stereo component system! Such an astronomical different experience from my last Saturn!

The worst is that I still recall with great sadness how beautifully my 1995 SW2 ran for the 14 years I had it (smooth engine, great A/C, sound system, and all) - until a falling tree crushed it. From personal experience, I can state that Saturn drastically lowered its mechanical quality across the board while increasing its aesthetic beauty. I hate to say it, but they created their own demise. After this 2001 SL2 heartbreaker, I have no sympathy or regrets for Saturn as a company.
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Old 10-22-2015, 08:18 AM   #16
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1998 SC2
Default Re: Rough idle in Drive, normal in Neutral

This will be of no help for you but it so happens that if any of the powertrain mounts, including the exhaust hangers, are not properly adjusted and OEM mounts used for the transmission and top engine mount you will have uncorrectable vibration issues. So if you buy cheap, low quality, mounts do not be surprised when the car has vibration issues.
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Old 10-22-2015, 09:08 AM   #17
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2001 SL1
Default Re: Rough idle in Drive, normal in Neutral

Quote:
Originally Posted by OldNuc View Post
So if you buy cheap, low quality, mounts do not be surprised when the car has vibration issues.
Not that it matters much now but he addressed this in post 8 where he mentions replacing all the mounts with OEM.
...
1999 SL2 MT (311,300 km @ 01/2023)
2012 Ford Focus SEL HB MT
2011 Suburban LT

Past Saturns
2001 SL1 MT (438,500 km 11y)
1993 SW2 AT (10y)
2001 LW200 MT (3.5y)
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Old 10-22-2015, 11:55 PM   #18
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2001 SL2
Default Re: Rough idle in Drive, normal in Neutral

Quote:
Originally Posted by trottida View Post
Not that it matters much now but he addressed this in post 8 where he mentions replacing all the mounts with OEM.
Thank you, Trottida! Yes, I did have every mount replaced with OEMs...with no improvement in vibration. But I finally gave up when the CD & cassette players, the sunroof, and the A/C system all failed within a month. Despite this car having every luxury option, every one was failing, and the car had not been in any accident or unduly rough circumstances. I had a true "lemon", but from checking around, there must have been many Saturn lemons turned out around that time.
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Old 10-23-2015, 12:40 AM   #19
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1998 SC2
Default Re: Rough idle in Drive, normal in Neutral

There is much more than just installing OEM mounts.

OEM top mount, trans mount, late 97 or newer torque axis struts and the polly inserts. Engine must have an even smooth idle. That means good even compression. Clean flow balanced injectors. The 3 rubber exhaust mounts should not be stretched when the car is at rest, just supporting the exhaust. These 3 suspension pieces will be what couples the exhaust vibration into the floor pan so the stretchiness and thickness of these is how you tune them to not appear solid at some inconvenient RPM. The Walker 35119 isolator is thicker than the original OEM. They are cheap so modifying them is not a big deal. They thin nicely on a belt sander but if too thin they break and you will be buying a new exhaust.

If you have an uneven idle you will never reduce the vibration to zero. Setting the torque axis struts to zero tension/compression at rest is critical.

The torque axis struts are of 3 different designs and the 3rd design, late 97 production, have replaceable inserts. These are the stamped and welded design. There are 2 pictures in my gallery. What you are attempting to accomplish is restrain the engine free motion as much as possible without going solid. The main axis of rotation is on a line between the top mount and transaxle mount. The torque axis struts are positioned to restrain the normal torque reaction and drive axle wind up. The poly inserts allow enough motion to not act as a solid link but do not transmit vibration well either. The idea is to keep large excursions of the engine/transmission and exhaust to a minimum. Small displacement of the power train transmits to large displacement in the exhaust. The rubber hangers will deftly transmit this exhaust motion into the floor pan which simulates the head on a large kettle drum, with you inside of it. You can get a buzz in the floor that does not transmit into the upper frame or seats but the large low frequency pan displacement is pushed up to a higher frequency. the characteristics of the rubber mounts determines where this buzz occurs. The trick is to get it somewhere you do not care. By minimizing the powertrain displacement you minimize the magnitude of the exhaust displacement you have to deal with. You can slightly change the static exhaust position to take all the stress off of the flex connector and have the mass of the exhaust evenly spread over the 3 mount points. The muffler hanger basically controls axial twist on the exhaust. I used the Walker 35119 isolators and just stuck them on. Ended up with the buzz from about 50 to 57mph and this is a speed range that is only passed through so I did not pursue any further elimination. the bed liner should kill this 50-57 mph buzz all by itself. The OEM isolators are a softer rubber and thinner and would possibly isolate the floor better but as they were 10+ years old and I am adverse to dragging the exhaust down the road I decided to replace them. The harder-thicker isolator appears as a solid at given frequencies.

Bolded text is covered in more depth in Ph #3. If you do not tune up the exhaust you can get some impressive vibration.

This is a power train mounting system and not some collection of random parts. They all must function together to damp out vibration.
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Old 05-29-2023, 10:56 PM   #20
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1999 SL1
Default Re: Rough idle in Drive, normal in Neutral

I recently experience a similar problem with my 1999 Saturn SL1. I would get rough idle at around 650 RPM that would go away when I shifted to Neutral or Park, which would cause the RPMs to increase. I replaced the oxygen sensor at the front of the car, and the problem partly went away. I still have rough idle at 750 RPM but not at 650 RPM. The spark plugs have less than 1,000 miles on them. I changed the spark plug wires, EGR valve, and cleaned the coil packs. My engine coolant temperature sensor is a brass tipped one. The old oxygen sensor was covered with a light gray ashen residue. If the oxygen sensor is marginally functioning due to being covered in residue, then a higher rate of airflow will make the oxygen sensor detect more oxygen.
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