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P0307 Code Repeatedly Appears in 1997 Dodge Ram 1500 5.2L - Misfire on Cylinder 7

Model: Dodge Ram 1500 Fault Code: P0307 Posted: 2005-08-04 06:27

I'm completely stuck with my 1997 Dodge Ram 1500 5.2L, which has reached 80,000 miles. The vehicle now repeatedly triggers the MIL (Malfunction Indicator Lamp) with a P0307 code—indicating a misfire in Cylinder 7—within just 10 to 20 miles of resetting the code. This issue first appeared about one year ago. After initial reset, it would disappear for a while. Around September 2004, I replaced spark plugs, ignition wires, coil, rotor cap, and had fuel injectors flushed. The next day, the P0307 returned. A second flush resolved the issue temporarily. The problem resurfaced again in March of this year. At that time, TSB 18-48-98 was applied—re-routing coil and plug wires with additional insulation. However, just one week later, the P0307 reappeared. We then ran a combustion chamber cleaner, which inadvertently fouled two plugs (a known side effect). After installing new plugs and flushing injectors again, the issue remained resolved for nearly a month. In May, the code returned once more. During our annual state inspection, we cleared the code and waited for sensor readiness—successfully passing the inspection. Unfortunately, just one day after the emissions test, the P0307 reappeared. Recently, I performed a compression test: all cylinders showed readings between 130–144 psi, with Cylinder 7 at 138 psi (within normal range). We also swapped the fuel injectors for Cylinders 5 and 7 to rule out injector failure. The engine runs smoothly under load and shows no knock or surging in fourth gear. The misfire only occurs during idle in gear or when decelerating from 20 mph—such as stopping or making a slow turn. If I shift out of gear and maintain idle above 1,000 RPM, the issue does not occur. I recently cleaned the throttle body and replaced the Idle Air Control (IAC) motor ($50), but symptoms persist. When the P0307 appears, there is a noticeable slight shimmy at idle—clearly indicating a misfire in Cylinder 7. The engine runs fine otherwise, and clears the code after reset. However, once the misfire occurs, it remains consistent on Cylinder 7. What could be causing this persistent issue? Any insights or diagnostic suggestions would be greatly appreciated.

Related fault codes
P0307
Comments (3)
Anonymous 2005-08-27 14:39

Additional detail: The P0307 only appears when idling in gear or during deceleration from 20 mph—such as stopping or turning slowly. If I shift out of gear and maintain idle above 1,000 RPM, the issue does not occur. After cleaning the throttle body and replacing the IAC motor ($50), symptoms remain unchanged. The misfire consistently affects Cylinder 7. When triggered, there is a slight but noticeable shimmy at idle—clearly indicating a missing spark or combustion event in that cylinder. Once cleared, the truck runs smoothly. Any further ideas on diagnosing this specific P0307 issue would be highly appreciated.

Anonymous 2005-10-04 17:21

I experienced the same pattern—first Cylinder 3, then both Cylinders 3 and 8, eventually leading to a random cylinder misfire. I did all the same repairs as described: plug replacement, wire re-routing, injector flushing, etc., but nothing resolved it. Eventually, I discovered that pre-hemi engine heads are prone to cracking—especially between intake and exhaust valves. Upon removing both heads, I found small hairline cracks in two cylinders. This explains why the misfire occurs intermittently at idle and causes rough running under light load. My truck runs fine at higher RPMs but stalls or shimmies when idling. This may be a similar issue with your 1997 Ram 5.2L.

Anonymous 2006-01-10 14:44

I suspect a blown plenum gasket in the intake manifold—a known issue on 5.2L and 5.9L Dodge Rams. Does your truck show any oil consumption between oil changes? Additionally, ignition coils are also a common failure point on these models and could contribute to misfires, especially in older units like yours. A leaky gasket or failing coil may cause intermittent misfiring specifically on Cylinder 7.