Random misfire at idle. I started using STP fuel injector cleaner (varieties) for last resort. Browse: OBD Code Library Where can I learn more about reading OBD codes? At idle it is mostly at cylinder 4 and also 3, and at higher rpms its mostly 5 and 8, but almost every cylinder misfires at some point. I have a 2007 accord ex-l v6 with 130,000 miles and i had got these codes and I have a misfire only on start up then it clears up around 10 seconds later I’m not sure what it can be any help is The P0301 trouble code means the engine computer detected a misfire in cylinder 1. Random misfire plus misfire in 2 and 4. 5l 240xxx on the truck, 160xxx on new motor, and I have a random misfire on cylinders 3 and 5, 5 more so than 3. I'm somewhat capable of performing most routine maintenance, but chasing misfires isn't my something I do everyday. If I am not mistaken, I realize that bad O2 sensors can cause a lot of these issues creating multiple codes along with misfires, rough idle, etc. Check Price. Bad Gas Symptoms Car explains what is bad gas, what happens when gas goes bad, misfire causes, no start problems, and check engine light warnings. Jun 23, 2025 · If your car is misfiring at idle or low RPM, schedule a visit with your mechanic. Misfire under load in cold air: ignition parts struggling to fire under higher cylinder pressure, or a lean condition from unmetered air. Fuel-system misfire symptoms will suddenly appear and are often more noticeable at idle than at highway speed. Truck would go like a banshee but the flashing check engine light wouldn’t go away. 5) Intake Manifold / Gasket Leaks (High Idle, Lean Codes, Random Misfire) Intake gasket leaks can cause lean conditions, random misfires, and idle problems—especially as seals age and harden. Failing O2 sensors? Failing idle-control valve? Time to give up and take it to the shop? What should I look for in my scanning software? (previous question: Lack of power when cold under load) edit: plugged in the scan tool when I got home. I chose STP because it had ingredients printed on. The codes kept coming back. 0. 0L Maintenance/Repairs misfire , mazda6 12 17743 September 23, 2014 Rough engine, power is low/surges, misfires when cold Maintenance/Repairs subaru , rough , forester , misfire 7 4926 June 5, 2014 Moisture and Misfire Maintenance/Repairs ford , misfire , sparkplugs 6 15141 February 11, 2014 Ignition Well, i have bad compression on rightside bank, runs ok, occasional random misfire code, anyone running same issue, think i may just run it till she dies. As the spark plugs age and the miles go by, the center electrode wears out, and the spark plug gap increases. ) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily! Neil I said: . The spark plug leads or spark plug wires transfer high voltage from ignition coils to each spark plug individually. Next i turned my attention to the rough idle. Vacuum Leaks. Generally, a misfire is a situation whereby one or more cylinders do not produce power due to some reasons. I've read most threads on the subject (much appreciation!), and will try some more solutions today. . 5X the legal limit, or if the misfire rate is high enough to cause possible damage to the catalytic converter. Posts: 54 Likes: 4 From: Ortonville, Michigan Random Misfire Issues - No obvious culprit How to Diagnose a Bad Fuel Injector – Step-by-Step Testing Guide Rough idle? Random misfire? Poor fuel economy? Before replacing your fuel injectors, you need proper testing. Today we're going to go over a simple fix which may be affecting your GM Truck. Introduction The P0300 code is a common and critical diagnostic trouble code (DTC) that appears on Ford vehicles and many others. Random misfires (p0300, P030x, P035x), the codes listed at times 12 different Some vehicles place it slightly left or right of center, but it’s typically easy to access. Final Takeaway Techron can work when deposits are the real problem and symptoms are mild. An engine misfire at idlecan be an aftermath of an incorrect air-fuel mixture, faulty oxygen sensor, vacuum leaks or a faulty catalytic converter. I'm open to any input. Knowing that spark plugs should be changed every 60,000 on my mini, I tried that first. 7L and 23000 miles that had a rough idle and extended crank but never threw any codes. Rough Idle, Random Misfire (Solved) Discussion in ' 3rd Gen. A cylinder-specific misfire is usually caused by ignition problems (spark plug/coil), fuel delivery issues (injector), vacuum leaks affecting that cylinder, or mechanical problems like low compression. No change after two tanks is a solid clue that your issue sits elsewhere. 2003 GMC envoy 200,xxx miles Bought this truck with over 6 codes lit up only issue was rough idle and misfire. But when I'm at 1000 -1500 rpm parked it sounds like there is a misfire, when driving she's very sputtering. LTFT is back up to 0%. Apr 20, 2023 · Further, in this article, we’ll discuss what engine misfiring is, the symptoms of engine misfiring, the five causes of why a car misfires at idle only, and how to fix a car that misfires at idle. I've got a 2007 Silverado 2500HD 6. The set I replaced weren't in bad shape, but it was probably time for a changing. Idle is rough, car shakes, rpm is at around 600. ” Unlike codes like P0301 (misfire in cylinder 1) or P0305 (misfire in cylinder 5), P0300 means your Jeep’s engine computer (PCM) can’t pinpoint a single cylinder as the culprit. My acceleration is still ass compared to when I got the truck. Hopefully you all can help me out. Two weeks later got a flashing CEL with misfires on cylinder 1 and multiple random misfires. What are the most common OBD-II trouble codes? Common codes include P0420 (catalyst efficiency), P0300 (random misfire), and P0171 (system too lean). it needed a battery, starter, all new steel brake lines and the 12v ign feed to In this article, you’ll learn what misfire at idle is, how you can locate the reason and fix the problem to avoid other issues with the engine in your vehicle. P0449 p0300 p0134 p0135 p0154 p0442 What I fixed so far: Injector bank 2 had a broken/ damaged wire (now I can hear all injector open and close) Broken spark plug (#1) changed all Furthermore, carbon buildup on the intake valves can create random misfires, further complicating the idle issue. Understanding these codes helps to focus your repair efforts efficiently. I fought the thing all winter. Vacuum leaks refer to any air that enters the combustion chamber without going through the MAF (mass air flow) sensor. The cam sensor had been replaced but turns out the oil pump drive that the cam 2004 - 2008 Ford F150 - ANOTHER 5. And here's what's interesting. Learn symptoms, common causes, step-by-step diagnosis, proven fixes, and typical repair costs to prevent catalytic converter damage. 0 Vortec with a PO300 random misfire/rough idle issue. 3 6. the code has changed from Random misfire to Random misfire and cylinder #1 misfire . First dealership replaced the vapor management valve but it didn't fix it. I've been experiencing some random misfire lately on my '02 5. But it's only the right side cylinders 1, 3 and 5 that misfire at idle. The aftermarket radio flickers a lot and there is a weird clicking noise under the dash (sounds like blinker or hazard clicking sound). In this guide, I’ll walk you through the 8 most common reasons engines misfire at idle, how to diagnose them before catastrophic damage occurs, and critical fixes to prevent engine destruction before your misfiring engine fails completely. I did all the obvious, coils, plugs, computer, cleaned injectors, no help. some stalling at idle. Note codes related to misfires, such as P0300 (random/multiple cylinder misfire) or P0301-P0308 (cylinder-specific misfire). Ive changed plugs and coil packs, checked everything with my evap system multiple times. Spark Plugs. 6 8 cyl. Idle gets shaky, power comes and goes, and the dash light may blink. I plugged my handy scanner and came up with misfires on all four cylinders as well as a random misfire code. Tacomas (2016-2023) ' started by eugenewithanaxe, Mar 6, 2022. . 150k miles on the truck. 8t… bought 4 iridium plugs. P0300 means random/multiple cylinder misfires. Jump to Latest 50K views 53 replies 15 participants last post by amc49 Sep 13, 2025 bswift79 Discussion starter Took the car from dealer, MPG was somewhat improved after the job, idle and engine sound was different. I unplugged bank 2 upstream o2 sensor and the misfire continued. A misfire can also occu Nov 16, 2025 · Discover what causes engine misfire at idle and learn the main reasons, symptoms, and fixes. runs better but 2001 Lincoln Town car 4. Clogged Fuel Injector. 3L, 223k miles, no codes. One time Hey Guys - Just found this forum. This issue can lead to poor performance, increased emissions, and potential engine damage if left Yes, a failing EVAP canister can trigger misfires when excess fuel vapor or unwanted air reaches the intake and shifts the air-fuel mix. 3. Cylinders 5' 6' and 8 are misfiring and a loss of power. A different shop recently (for this symtom) replaced; spark pugs, MAF, Throttle Body, and the Alternator. A faulty O2 sensor can skew fuel trim enough to create rough running and, in some cases, trigger misfire counts or misfire codes. If misfires return quickly, look for oiling issues or intake leaks rather than replacing plugs repeatedly. Prompt diagnosis and repair are vital to prevent further engine damage and restore optimal vehicle performance. Well, here is my story. Spark Plug Leads. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc. If your engine is chugging at a stoplight but smooth at speed, take a hard look at the fuel system. It all started 4 months ago. Simple, clear guidance to help you diagnose and prevent misfires. I think the reason I don't get the code if I put it in drive and take off immediately is that it doesn't run the misfire diagnostic if it's not allowed to sit at idle for a certain amount of time (something about the GM driving sequence). It has 181000 miles on the clock. Took it to a Just bought a 1le ss, code for p0300 popped up (no other code but that) idles rough, just changed spark plugs but nothing any suggestions? I had a similar thing but mine would smother out like no fuel and would show different cylinder misfires on the 4. Liqui Moly 2007 Jectron Gasoline Fuel Injection Cleaner – 300 ml , blue. #CarRepair #MechanicLife #EngineDiagnostics #IgnitionCoil #CarMaintenance #वायरल (Viral) #आजकीखबर (Today's News/Update) #ट्रेंडिंग (Trending) #इन्स्टाहिन्दी (Insta Hindi) #देशदुनिया (Desh Duniya) P0350 ignition coil primary/secondary circuit P0351 ignition If you run a scan tool, log long-term fuel trims and misfire counts. P0300 Random Misfire with no luck pinpointing it. I own a Skoda superb (2023, 2748 km, Diesel) and I am getting a P0300 random or multiple cylinder misfire code along with a check engine light. and the same with the MAF sensor and low fuel pressure. Subject: Cold Engine Idle Misfire Or DTCs P0171 P0174 - keywords 4. Can someone share some advise on how to test CAR: a 98 grand prix gt 3. Understanding these issues can save you time and costly repairs, as early detection is key. I have a 2006 Colorado WT 4X4 3. Check and Replace Spark Plugs One of the most common causes of engine misfires is worn or faulty spark plugs. HISTORY: car sat for a lil over a year, i bought it with a 153k miles 3 months ago. Got a rough idle and a misfiring engine? Let Champion help you diagnose a few common issues and causes related to misfiring. 8. 7K views 5 replies 5 participants last post by davester3500 May 19, 2024 If it is P0300, that means a random misfire, a misfire that is happening on multiple cylinders. This leads to slower acceleration or brief loss of power in the engine. Thoughts? 105/119/145 204K Have 5 codes all are cylinder misfires, the 5th code is random multiple cylinder misfire. As far as the crank bolt, have your dealer check to see if you are covered under the recall. I changed plugs, coils, and Jeep Liberty 2012 3. Mar 8, 2023 · In this article, you’ll learn what misfire at idle is, how you can locate the reason and fix the problem to avoid other issues with the engine in your vehicle. 4 and it is driving me crazy. I still havent sorted out my idle / misfire issues due to no one responding to my other posts, so maybe i'll get lucky third time??? Anyways so im going to try this again. The truck runs rough at idle, though smoothes out as the rpm's rise. Problem would come and go. Still couldn’t get rid of the P0300 random misfire code and rough idle. Learn symptoms, common causes, diagnosis steps, proven fixes, and typical repair cost ranges to prevent catalytic converter damage. The P0300 code, indicating a “Random/Multiple Cylinder Misfire Detected,” is a common headache for Jeep owners, whether you’re a seasoned off-roader or a weekend DIY enthusiast. engine light and misfire. The engine feels unsteady, runs rough, and the car shake I have a 2022 BD with 2. The o2 code and misfire codes come back right away after clearing it. 157k miles ISSUE: p0300 -random multiple cyl misfire, p0306 -cyl 6 misfire. 1. All spark plugs have a specific pre-set gap between the center electrode and the J-shaped ground electrode. Detailed Explanations Symptoms of P0305 Cylinder 5 Misfire A misfire in cylinder 5 typically presents with several noticeable symptoms: Illuminated or flashing check engine light Rough idling and engine vibrations Loss of power, especially during acceleration Poor fuel economy Possible fuel odor from exhaust Engine hesitation or jerking In severe cases, the engine may even stall at idle or Help us help you. Beyond those RPMs it sounds fine. P0171 was gone but random misfire codes continued. 8 5. I now have a bad misfire. First - 2003 GMC 2500hd 6. P0302 Random Misfire on 2006 Mazda6 V6 3. This happens on cold starts when the car calms down after starting A random P0300 misfire code or cylinder specific misfire codes (P030X) will be set when the OBD II system detects misfires that may increase emissions 1. 7L often faces random misfires and rich running conditions causing poor fuel economy and rough idle. A diagnostic scan can pinpoint the issue, and the check engine light may provide clues about the cause. Scan codes and you might see EVAP faults sitting next to misfire codes. Lastly, a malfunctioning camshaft sensor can disrupt the engine's timing and performance, contributing to rough idling. Click to expand You still need to review fuel trim and upstream oxygen sensor values for bank 1, driver side with engine running and fully warmed up. She runs great at highway speeds but at idle and during The rought idle is fixed , I believe the random misfire gone too. The P0300 code is a generic powertrain diagnostic trouble code (DTC) that indicates a “Random/Multiple Cylinder Misfire Detected. Spark plug leads are something you will find on older engines with distributors or wasted spark ignition systems. 0 air cold crack hesitate idle intermittent internal intake leak lean misfire miss P0171 P0174 P0300 power rough surge vacuum #PIP3232B - (02/07/2007) Models: 2002-2005 Cadillac Escalade 1999-2005 Chevrolet Avalanche, Express, Silverado, Suburban, Tahoe, Trailblazer Cold start rough idle w/ random multiple misfires irregular fuel pressure Jump to Latest 3. You may get engine trouble code (MIL Light) P0300 which is a "Random Misfire Code". A misfire can feel like the engine is tripping over itself. Random misfire plus rough idle: vacuum leak, dirty throttle body, clogged injector, low fuel pressure, or an EGR issue on engines that use it. It signals a "Random/Multiple Cylinder Misfire Detected," meaning the engine control unit (ECU) has noticed that one or more cylinders are not firing correctly. I suspect I might have a coil that acting up. Overheating that returns after coolant top-offs Coolant loss with no external leak you can spot Bubbles in the radiator or overflow bottle after warm-up White exhaust vapor that lingers after the engine is hot Rough idle or random misfires, often on cold start Oil that turns milky or foamy on the dipstick or cap Discover more answers What causes random misfire on the 2001 ford explorer mainley #8 cylinder? I get a multiple misfire and misfire cylinder 6 at an idle. P0303 means cylinder 3 is misfiring. A drop in random idle misfires can hint at a cleaner spray pattern. Bringing fuel into the combustion chamber isn’t the only job of a fuel injector. See post #6 Oct 30, 2018. 4 rough idle, runs rich woe - I've got a 2007 F150 KR with the 5. 7L Random Misfire and Running Rich Issue Liberty 3. If it was a P0302 which I think is misfire cylinder 2, I would think about doing stuff like changing coil packs, plugs, plug wires, injectors. Let the car cool down and it will again begin to have misfires at idle, and ruff idle. The extra air that isn’t accounted for by the MAF sensor will make the air/fuel mixture lean and cause misfires because it takes longer to burn. It's literally only at idle that I notice the misfire (barely). Anytime I have a random misfire code in one bank (1,3,5 or 2,4,6) I go right to the timing belt and check cam timing. 0 - 170k Fairly Recent Fuel Pump, Spark Plugs, Oil Change, Cleaned TB and MAF sensor I just pulled exhaust manifolds and replaced the gaskets. The P0300 Chevy code signals a random or multiple cylinder misfire, which can stem from ignition, fuel, air, or mechanical issues. Told the guy I was gonna replace them and he said this. Only at an idle/low Only codes it has is p0300 random misfire and bank 1 sensor 2 o2 sensor low input. Just changed plugs, wires and injectors. 5ux2, rgpeiz, eyzj4, puhg, cnq6z, knfz, bpdbi, qbgv, ao6fk, spbllz,