On today’s segment of #troubleshoottuesday we want to help you diagnose engine stumble and stalling. Usually this type of issue will happen out of the blue and catches you at the worst possible time. Typical symptoms include engine stumble or stalling when coming to a stop or when accelerating. These issues are also commonly described as engine misfires, hiccups, jerking, or “running rough”. The best piece of advice is to always start with pulling codes from your vehicle, however, in lieu of having any codes here are some diagnostic areas you can look at:
Engine Stumble or Stalling When Stopping
- If equipped, have you cleaned and checked your IAC (idle air control) on your throttle body?
- Many vehicles have issues with the IAC gumming up with carbon and can cause either high idle or engine stumble conditions when coming to a stop. Since the IAC is not functioning during acceleration, you will typically only notice issues when the car is coming down to an idle.
- Have you verified that your TPS (throttle position sensor) is functioning correctly?
- If equipped with an automatic transmission, have you verified proper fluid level?
- We had a Jeep Wrangler TJ that would get about 1/2 – 1 quart low in transmission fluid resulting in an engine stumble or stall condition when slowing down to a stop.
- Have you done a tune up? Are you sure that you spark plugs / wires are in good shape, properly gaped and free of oil contaminants?
- Is your air filter clean and free of all blockage that could choke the engine out?
- Do you have moisture around your spark components (coil packs / distributor)
- Sometimes sitting water can get into your spark components and wreak havoc, especially if your vehicle has a distributor.
- Pro tip – you can spray WD-40 inside / outside of your distributor cap and plugs to see if the problem goes away. If it does, you have an issue with the components that you have sprayed WD-40 on that is causing a short. Safety tip – only spray WD-40 on a cool car and away from flames as it can be flammable.
- Is your vehicle equipped with an EGR (exhaust gas re-circulation) valve? If so, is it leaking and or functioning?
- Do you have any exhaust leaks close to the head of the engine?
- Have you cleaned your MAF (Mass Air Flow) Sensor and insured that it is working correctly?
- Have you checked to make sure that your vehicle does not have any vacuum leaks?
- Have you conducted a compression test to rule out internal engine issues such as a bad head gasket, bent valve, broken piston ring, etc?
- Have you checked your fuel pressure?
Engine Stumble While Accelerating
In addition to checking everything listed above, engine stumble while accelerating can also be caused by the following components:
- Have you checked your ignition timing with a timing light?
- Have you checked your fuel injectors or carb if you have one?
- Have you checked all electrical connections and grounds to make sure they are free of corrosion and have good connection?
- Have you checked the readings on your O2 sensors to verify that they are working correctly?
- Lazy or bad O2 sensors can cause most of their problems under acceleration conditions where the air fuel mixture is far less stable than at idle.
- Have you checked your catalytic converter (CAT)?
- If a CAT is clogged it can choke the engine and cause engine stumble while accelerating. Sometimes you can tell if the CAT is clogged by taking a hammer and lightly tap the CAT and listen for loose particles jingling around. If you hear particles within the CAT when you tap it, your catalytic converter is coming apart.
The below image shows a 1996 3.8L V6 Camaro to demonstrate where the IAC, TPS, MAF and EGR would be located. Every car is going to be a little bit different, but the IAC and TPS will always be located on your throttle body. The MAF if your vehicle has one will be located somewhere between your air filter and your throttle body as it measures the air that goes into your engine and is used in fueling calculations.
We hope the above article has helped you diagnose your engine stumble and stalling issues. To subscribe to our posts be sure to enter your email into the subscription box to the right if you are on a desktop and at the bottom of the page if you are on mobile. You can also follow us on Instagram @highperformancejunkies
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