My moms GMC Yukon has been acting funny lately when she first starts it the engine sputters and runs rough but within a minute it idles fine and runs normal....recently it had plugs wires and fuel filter replaced so doesn't need a tune up....it has been cold here lately which is the only difference I can tell...I checked for vacuum hose leaks and none also one time her check engine light flashed and then stayed on the code was for lean condition bank 2...I cleared it and it has not come back on since but the car still idles rough at start any ideas would be appreciated?
Sputtering Engine
- Thread starter 4x4chevydude
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might be a good idea to know the year. JMO.
Like maybe the distributor cap is cracked..... lol
Like maybe the distributor cap is cracked..... lol
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we need to know engine size also, but it sounds like it is a 5.3 or a 6.0 maybe. If that is the case replace the intake gaskets and make sure the manifold is smooth and mostly flat. There was a bullitin about this on some of the late model engines from 199 forward. Replacing the gaskets on these engines is farily easy and doesn't take much time, remember to clean t body also.
Originally Posted By: yonyon
I'm with vssjim on this one. If you've got a C/K truck with an LSx in it a rough idle when cold means you need to check your intake gaskets. If they leak you shove some new ones in there and all will be well.
I'll 3rd this...
I'm with vssjim on this one. If you've got a C/K truck with an LSx in it a rough idle when cold means you need to check your intake gaskets. If they leak you shove some new ones in there and all will be well.
I'll 3rd this...
Do you have an Android phone? If so, invest $20 and buy an ELM OBD-2 Bluetooth adapter, and the $5 Torque app.
Vague codes like "Lean Condition" or "Rich Condition" or "Misfire on Cyl 1" can be hard to diagnose by the code itself.
With the Torque app you can watch sensor data in real time. Coolant temp, oxygen sensor output, PCM long & short term fuel trims, MAF airflow, intake air pressure, the list goes on and on. It may take a little bit of Google research to learn how fuel injection works on these more advanced engines, but having this info at your fingertips helps a GREAT deal.
For example, I had an ex's mid 90's Chevy pickup with 5.7L engine would occasionally sputter and die while coming to a stop. Code showed up as "coolant temp sensor." So in went a $15 coolant temp sensor. Problem remained.
With the phone hooked up wirelessly to the OBD-II port, I could monitor coolant temp real time from the passenger seat on my phone. As the truck came to a stop, and sometimes when hitting a bump, the coolant temp would nosedive to like -50F. But it would quickly jump back up. In cruising conditions, that absence of coolant temp data (or rich mixture from a -50F reading) wouldn't bother the truck as the engine was running fast; it'd hardly skip a beat. But when coming to an idle at a stop, when the coolant data went wacko for a split second, it was enough to stall the truck.
The point is, without this data, I was unable to tell that it was actually a loose wire in the *connector* of the coolant temp sensor. When the truck hit a bump, or came to a sudden stop, it was enough to break the connection.
When monitoring the data while the engine's running good, you'll know what to look for, or something will become immediately apparent when it's not running good.
Just a handy inexpensive app I recommend any gearheads to purchase if they have an Android cell or tablet. I swear I don't work for either company
Vague codes like "Lean Condition" or "Rich Condition" or "Misfire on Cyl 1" can be hard to diagnose by the code itself.
With the Torque app you can watch sensor data in real time. Coolant temp, oxygen sensor output, PCM long & short term fuel trims, MAF airflow, intake air pressure, the list goes on and on. It may take a little bit of Google research to learn how fuel injection works on these more advanced engines, but having this info at your fingertips helps a GREAT deal.
For example, I had an ex's mid 90's Chevy pickup with 5.7L engine would occasionally sputter and die while coming to a stop. Code showed up as "coolant temp sensor." So in went a $15 coolant temp sensor. Problem remained.
With the phone hooked up wirelessly to the OBD-II port, I could monitor coolant temp real time from the passenger seat on my phone. As the truck came to a stop, and sometimes when hitting a bump, the coolant temp would nosedive to like -50F. But it would quickly jump back up. In cruising conditions, that absence of coolant temp data (or rich mixture from a -50F reading) wouldn't bother the truck as the engine was running fast; it'd hardly skip a beat. But when coming to an idle at a stop, when the coolant data went wacko for a split second, it was enough to stall the truck.
The point is, without this data, I was unable to tell that it was actually a loose wire in the *connector* of the coolant temp sensor. When the truck hit a bump, or came to a sudden stop, it was enough to break the connection.
When monitoring the data while the engine's running good, you'll know what to look for, or something will become immediately apparent when it's not running good.
Just a handy inexpensive app I recommend any gearheads to purchase if they have an Android cell or tablet. I swear I don't work for either company
Aside from my first post perhaps straying off topic..
If the engine quickly resumes normal operation after a short warm-up, maybe entering into closed-loop with oxygen sensor feedback is what's curing the problem?
That could point to a few sensors that are used in open-loop operation (coolant temp, air intake temp, MAF, throttle position, etc.) as mixture is derived from a map based on those inputs before the oxygen sensor is sufficiently warmed. Maybe one of them is out of whack, that the oxygen sensor input is helping to compensate? OBD-II is usually pretty good at narrowing this stuff down close enough that solution isn't TOO far beyond reach.
If the engine quickly resumes normal operation after a short warm-up, maybe entering into closed-loop with oxygen sensor feedback is what's curing the problem?
That could point to a few sensors that are used in open-loop operation (coolant temp, air intake temp, MAF, throttle position, etc.) as mixture is derived from a map based on those inputs before the oxygen sensor is sufficiently warmed. Maybe one of them is out of whack, that the oxygen sensor input is helping to compensate? OBD-II is usually pretty good at narrowing this stuff down close enough that solution isn't TOO far beyond reach.
Sorry rookie mistake 2003 with a 6.0. I thought of the intake gaskets but those are solid...i think 92saturn has a good starting point with sensors ill have to get a good scanner because it definitely only does it in open loop. Thanks for the ideas!
Could very well be the intake manifold gasket. If the engine has a MAF (I believe it does, but not sure), air will bypass the MAF so it doesn't get metered, which will lean your mixture out. A lean mixture, especially at startup in the cold will certainly result in rough running.
I suspect what's happening is that once the oxygen sensor joins the fun (takes a few seconds to a minute or so depending on temp), the PCM sees the lean mixture and adds fuel, which will result in a positive fuel trim. This will smooth out the engine and cure the sputtering. If the fuel trim crosses a pre-set threshold, a lean code gets set. You'll definitely see this behavior on a scanner, specifically the long term fuel trim-- but the symptoms are probably enough to identify the intake manifold as the culprit even without one.
I suspect what's happening is that once the oxygen sensor joins the fun (takes a few seconds to a minute or so depending on temp), the PCM sees the lean mixture and adds fuel, which will result in a positive fuel trim. This will smooth out the engine and cure the sputtering. If the fuel trim crosses a pre-set threshold, a lean code gets set. You'll definitely see this behavior on a scanner, specifically the long term fuel trim-- but the symptoms are probably enough to identify the intake manifold as the culprit even without one.
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