Rough Idle

Hello,

It sounds like the fuel pressure is low which will cause the issue. Check fuel pressure with a gauge here is a guide it should be 50-60 psi key on engine off and hold.

Here are two guides to help us fix the problem

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

and

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Please run down these guides and report back.

Just an update...I listened to each injector and they are all working. I took the intake system apart and the filter was clean, the MAF does not look like there is any damage or anything that is visibly broken. I took the throttle body off and cleaned it. It had pretty thick build up on it so I got it completely clean. Cleaned as much of the actual intake as possible. I changed the throttle position sensor a while back. The Haynes manual says that there is a PCV sensor/valve, but when I went to the parts store (all 3 big ones) none of them had it and they said that it wasn't equipped with one? I read online that some of the lifters could be bad, but wouldn't have other issues???

Thanks,
Gus

HMAC300,

Thanks for the quick reply. I did have the fuel/pump assembly just replaced last year, but I will check the pressure again. The idle is rough while it is sitting still, not just isolated to after start-up. I have a friend who is a Chevy Mechanic and he put his computer on it and said that the pump was kicking codes. I replaced the pump and it worked after the initial start, but after I shut it off and restarted it never worked again. What I jumped was the power/ground (relay up under the Master Brake Cylinder) for the pump solenoid for it to turn it on.

As far as the idle I forgot in my last post that the problem still exists after cleaning the throttle body.

Thanks,
Gus

This sounds like the PCM is seeing the crankshaft sensor fail so it shuts the pump off here is the location of the sensor so you can change it out. Check the diagrams below.

Here is a video of the job being done on you car.

https://youtu.be/sKo7xRWVNqY


CRANKSHAFT POSITION SYSTEM VARIATION LEARN

1. Install a scan tool.
2. Monitor the engine control module (ECM) for DTCs with a scan tool. If other DTCs are set, except DTC P0315, refer to Diagnostic Trouble Code (DTC) List - Vehicle for the applicable DTC that set.
3. Select the crankshaft position (CKP) variation learn procedure with a scan tool.
4. The scan tool instructs you to perform the following:
1. Accelerate to wide open throttle (WOT).
2. Release throttle when fuel cut-off occurs.
3. Observe fuel cut-off for applicable engine.
4. Engine should not accelerate beyond calibrated RPM value.
5. Release throttle immediately if value is exceeded.
6. Block drive wheels.
7. Set parking brake.
8. DO NOT apply brake pedal.
9. Cycle ignition from OFF to ON.
10.Apply and hold brake pedal.
11.Start and idle engine.
12.Turn A/C OFF.
13.Vehicle must remain in Park or Neutral.
14.The scan tool monitors certain component signals to determine if all the conditions are met to continue with the procedure. The scan tool only displays the condition that inhibits the procedure. The scan tool monitors the following components:
- CKP sensors activity-If there is a CKP sensor condition, refer to the applicable DTC that set.
- Camshaft position (CMP) sensor activity-If there is a CMP sensor condition, refer to the applicable DTC that set.
- Engine coolant temperature (ECT)-If the ECT is not warm enough, idle the engine until the engine coolant temperature reaches the correct temperature.
5. Enable the CKP system variation learn procedure with a scan tool.

6. IMPORTANT: While the learn procedure is in progress, release the throttle immediately when the engine starts to decelerate. The engine control is returned to the operator and the engine responds to throttle position after the learn procedure is complete.

Accelerate to WOT.
7. Release when the fuel cut-off occurs.
8. Test in progress
9. The scan tool displays Learn Status: Learned this ignition. If the scan tool indicates that DTC P0315 ran and passed, the CKP variation learn procedure is complete. If the scan tool indicates DTC P0315 failed or did not run, refer to DTC P0315. If any other DTCs set, refer to Diagnostic Trouble Code (DTC) List - Vehicle for the applicable DTC that set.
10.Turn OFF the ignition for 30 seconds after the learn procedure is completed successfully.
11.The CKP system variation learn procedure is also required when the following service procedures have been performed, regardless of whether DTC P0315 is set:
- A CKP sensor replacement
- An engine replacement
- A ECM replacement
- A harmonic balancer replacement
- A crankshaft replacement
- Any engine repairs which disturb the CKP sensor relationship


Check out the diagrams (Below). Please let us know what happens.

Replace the crankshaft sensor, fixed

I own a 03 Chevy Suburban 4WD 5.3 liter. About a year ago..fuel pump quit and was replaced. Since then during start up in cold weather vehicle runs and idles rough…sometimes it will stall…After vehicle warms, runs fine. I have replaced the spark plugs, spark plug wires, and Mass Air Flow senor. I recently purchased a code reader which gave me the following codes P0171- System too lean (Bank1) and Po174- System too lean (Bank 2). Has anybody had the same problem?

The coolant temp sensor may cause temp related issues? You can clean throttle-body and iac/idle air control. Use a gage and check fuel pressure, key on engine off, first thing in the morning.

sounds like an o2 sensor had problem with a lebaron

I want to second JDLs recommendation to test the fuel pressure. This engine is very sensitive to fuel pressure. It requires a minimum of 55 PSI to run.

that is true he does need to check pressure never hurts. but that is similar to how my lebaron acted and ran fine after o2 sensor was replaced. can anyone help with stalling problem with my 01 galant?

scratch that sorry i did also have to replace my fuel pump as well as my o2 sensor again sorry for the mix up

We have replaced all 4 O2 sensors, and the mass air flow sensor, and fuel filter. It still has a rough engine idle when the car is cold and check engine light comes on. What now? Only 53,000 miles on it.

try running some injector and fuel system cleaner

Look niklis10, If you have a problem with your car, start a question about it but please refrain from giving advice to other people on a subject you have no knowledge in. This is not an 0/2 sensor problem.

Hey, is this a flex-fuel vehicle? If the mil comes on, check the codes. Some of the national brand autostores will check codes for free. Any code you get doesn't tell you what to replace, always check the wiring circuits.

Unmetered air can cause a rough idle, it may seal off after the vehicle warms-up.

that's why i replied (scratch that sorry i did also have to replace fuel pump as well as my o2 sensor!) and who are yo to say i have no knowledge in this iv been working on cars BY MYSELF since i was 13 so i think i might know a thing or 2. and i did post a question i thought when you were done with him you might be nice enough to help me guess not. and now look what this guy has to look at on his page. but hey thanks wrench and sorry monkey

First off, I was typing my response at the same time you were posting your last response so i hadn't seen it yet.
We don't address multiple questions or vehicles within the same question and it's very easy for me to see how much knowledge you have by the advice you give. There are professionals here on staff to handle the answers. You stick with the questions. You're only confusing people.

My Vehicle recently started to idle rough when I use the heater or air conditioner. It feels like its going to die while waiting at stop lights. Then today it has started to idle rough without the heater or air conditioner running. It would only do it every so often until now. Now its doing it every time I drive it. Also no check engine light or codes. I Also feel it while driving, almost feels like the transmission is slipping. But I know it is not the transmission. Also loss of power like the brake is on every time you accelerate. Do anyone have any idea what could be causing these problems?

Before you go looking for the hard stuff, charge the battery at a slow rate for an hour with a portable battery charger. Unplug the small connector on the side / rear of the generator, then drive the vehicle to see if the symptoms are different or cleared up.

If things are different, have the charging system tested for maximum full-load output current and "ripple" voltage. If current is exactly one third of what it should be and ripple voltage is high, the generator has a failed diode and will need to be replaced. The third potential symptom of a failed diode is elusive engine running problems. This generator design used by GM starting with 1987 models develops huge, harmful voltage spikes that can damage the internal voltage regulator, short one of the six diodes, and interfere with computer sensor signals. The secret is voltages can be "induced" into sensors' signal wires, and while the resulting voltages the Engine Computer sees are incorrect, they fall within the acceptable range, therefore no diagnostic fault codes are set. About half of the over 2000 potential fault codes will turn on the Check Engine light, so if there's no fault codes, there will be no Check Engine light either. The Engine Computer will accept the false sensor readings and try to run on them.

The most important part of my story is if the generator is found to be developing only one third of its rated maximum current and ripple voltage is high, you must replace the battery and generator at the same time to reduce the high number of repeat failures, . . . unless the battery is less than about two years old. Repeat generator failures on GM vehicles are very common, but it is mainly caused by those voltage spikes they develop, and those spikes are dampened and absorbed by the battery. Batteries lose their ability to do that as they age and the lead flakes off the plates. It might crank the engine just fine, but it's no longer able to absorb those harmful voltage spikes. If you don't replace the battery when this happens, it's common to go through four to six replacement generators in the life of the vehicle.

it happended all of a sudden while driving with no signs of any problem, engine stall, wouldnt start, after sitting engine start but would not idle and not enough power to move had to pump pedal to keep running. no engine light on, changed fuel filter and it got alittle better it would idle ok but when useing throddle have to pump to keep up rpm but would hold about 3500rpm steady for 5-6 seconds before having to pump pedal,I have owned my suburban for 11 years with no problem any thoughts on problem

scan for codes check fuel pressure first. put vacuum gauge on intake and if 15' or belwo at idle it may be a clogged converter

ok check codes had a random misfire fuel pressure good 54psi until it was running and had a slow leak down, replaced fuel pump but need to remove evap can and can't remove tubing alrdy broke one nipple and have no clue I am depressing the sides of clips but the do not release, what am i doing wrong lol

Removal

1. Raise and support vehicle. Locate EVAP canister, mounted to crossmember or left frame rail, near front of fuel tank. See Fig. 30 or Fig. 31.
2. Remove EVAP canister mounting bolts. Disconnect EVAP pipes at EVAP canister. Disconnect EVAP vent valve pipe at EVAP canister bracket. Remove EVAP canister.they squeeze together but you need to do this with cannister OFF the truck. It will be either mounted to frame or crossmember. crossmemeber shown..

We rescently had a tune up done to correct the rough idle problem. The car idles real low (500RPM and below), but does not stall out. It is real rough at this idle speed. Runs great otherwise.

Our mechanic says it needs a new alternator and battery. Do you think that is the problem. Seems to me that if the alternator was bad, it would create other problems.

Any ideas.

Thanks

Charles

Is the service engine soon light on? or the Battery light? If the SES is lit first thing you need to do is have the codes read, Autozone does it free, Post the results with the code number(s). Even if the service engine light is not on, there should be freeze frame data stored.

No check engine lights (or service soon engine lights) have come on.

Clean or replace the idle air control valve, it's bolted to the throttlebody

I have a problem with a slightly rough idle and stalling problem. The truck idles at around 500 rpm. when I rev the motor then let off the accelerator the rpm drops below 500rpm almost stalling and then idles at 500 again. When driving slowly and in parking lots it tends to stall when I let off on the accelerator. It seems to be ever so slightly missing at idle also. On the open road it seems to run fine. So far I have replaced, air filter,spark plugs,plug wires,fuel filter and the throttle position sensor. still have same problem. The check engine light has not come on at all. Please Help!!!!! THANKS..............

The fuel pressure regulators are very common for a leak and causing your symptoms.

I am guessing you don't have a fuel pressure gage.

Where I live they are easy to find at Auto Zone, and not too expensive. If you are going to be diagnosing your own vehicle very long, it will easily pay for itself in not wasting money on wrong parts.

it would help narrow down this one.

2002 Chevy Surburban, Southern California area, when (cold day) engine is started it idles at 1100RPM for about 30 seconds, then drops to about 600RPM, the engine is rough, service engine light comes on, sometimes will stall, if I hold accelerator down to get to around 1000RPM the RPM will not stay but fluctuate between 800 and 1200, after engine warms up seems to run normal. When started after intial warm up or on a warm day 60 degrees or hotter it still runs a little rough but only for a short time.

Could be the idle air control valve needs cleaning.

Have the computer scanned for code/s-you have a problem within the engine management system that caused the CEL to turn on-This is your starting point of diagnosis,finding out what's going on.

The mechanic said it was a generic code that code mean anything. Then he went on to say that my vehicle has a plastic intake maifold which warps that causes a vaccum leak and it could need replacing which costs 5K.