Sometimes my car has a rough idle and even stalls – 2004 Chevrolet Tahoe

ANSWER : Hello. From my experience with this engine, the issue is usually due to the fact that the throttle body plate is worn out in the bore, or, more commonly, it is caused by an issue with the intake manifold gasket leaking. I always scan for codes first and check the fuel trim readings which would tell me if this is an air leak issue. Then I check for leaks around the intake gasket. It can also be a failure in the MAF, but that is not as common.

If you want to have this low idle fixed, consider having a certified mechanic, such as one from YourMechanic, come to your home or office to diagnose why the car is idling rough.

ANSWER : This may be a result of a dirty or failing idle air control valve. The idle air control valve reads the air intake as it is mixed with fuel prior to being injected into the engine at low speeds and at idle. Since this valve is controlled by the vehicle’s computer, it will adjust idle speed based upon other measurements such as engine temperature, intake air temperature and electrical system load or voltage. When you accelerate, the engine RPM increases, and as you let off the gas, the RPM slowly returns to the normal idling speed with the help of the idle air control valve making the transition from a higher RPM back down to idle speed. When the engine RPM drops below the normal range of about ~800 RPM, this often times will cause the engine to stall indicating a dirty or faulty idle air control valve. I would recommend having an expert from YourMechanic come to your location to diagnose and repair your idle air control valve.

ANSWER : A number of components or faults can cause your issues. A vacuum leak can cause your issues. Depending on the vehicle, components such as the mass airflow sensor, throttle position sensor, coolant temperature sensor, and a number of others can be the cause. Since randomly replacing parts can get expensive as most electronic components are not returnable once installed, having a certified technician, such as one from YourMechanic, diagnose the stalling/surging is the best place to start.

ANSWER : A failing torque converter clutch solenoid is a common item to cause this sort of concern, but there are other parameters that must be looked into as well. A large vacuum leak can cause the engine to stall once the speed comes back down to idle, this is usually accompanied by a car that is difficult to start. Hire one of our mobile experts to diagnose your stalling issue and avoid an unsafe situation.

ANSWER : Failures in the charging circuit (alternator, etc.) do not typically cause a rough idle. A faulty throttle position sensor and/or clogged fuel injectors can cause the engine to run roughly but those are just two among many, many potential causes of a rough running engine. What will help you is a rough idle diagnostic during which the individual cylinder firing patterns can be evaluated on a scope. Those firing patterns will allow the mechanic to see if perhaps there is "a" or a couple bad cylinders and also whether the engine is experiencing a fuel system versus ignition system problem and in which cylinders. On an engine with so many miles, 240,000 in your case, compression should be tested in each cylinder as wear in the engine could potentially cause enough imbalance, from cylinder to cylinder, to cause the engine to run roughly. You have to keep in mind that typically there will be multiple issues with an old engine, for example you could have dirty fuel injectors, a sticky EGR valve and fouled plugs due to the inevitable leakage from old valve stem oil seals, or any of a number of other combinations. The best thing to do, to see if you can get additional service life out of the engine, and you likely can, is to methodically and carefully go through the list of possibilities. YourMechanic certified technicians specialize in just that so if you set up a diagnostic, a technician will get to the bottom of this for you and give you repair options so that the engine can be restored to reasonable operating condition.

ANSWER : The idle air control valve is common for causing a rough idle in many cars, but it sounds like you have already corrected that. Another thing you may also want to check is the crankshaft position sensor. A crankshaft position sensor monitors the position or rotational speed of the crankshaft. This information is used by engine management systems to control the fuel injection or the ignition system timing and other engine parameters. When this is faulty or not working properly, this will cause problems with the ignition system and generating spark transmission to the spark plugs resulting in starting problems, rough idling and other performance issues. You may also want to check the fuel pressure as low fuel pressure can also cause rough or poor idling if the fuel pattern being sprayed from the injectors is not consistent. This can also happen in the case of having dirty fuel injectors which may also interrupt the spray pattern of the injectors. I would recommend having an expert from YourMechanic come to your location to diagnose and inspect your car.

ANSWER : Hi there. The fact you able to get the idle speed to drop by tapping the gas pedal, lead me to believe the high idle is due to a sticking accelerator cable. Another possibility could be, a faulty throttle body not allowing the throttle to return to the closed position. Proper diagnoses should be performed to avoid unnecessary repairs. I recommend having your vehicles high idle be diagnosed and repaired by a certified technician, such as one from YourMechanic.

ANSWER : You should have the check engine light and engine scanned to see if the engine may be running lean due to low fuel pressures or clogged injectors. You should also have the mass airflow sensor cleaned and checked for proper readings and replace if not within specifications. The vehicle runs richer in colder weather and may be the reason for not stalling. You should clean injectors, clean throttle body and idle control valve then clean mass air sensor and relearn idle.