← Back to list

1999 Dodge Caravan 3.3L Engine Surging at 1200 RPM with P0171 and P0172 Codes - Diagnosis Tips

Model: 99 Dodge Caravan Fault Code: P0172 Posted: 2007-07-12 19:03

I own a 1999 Dodge Caravan with a 3.3-liter gasoline engine, currently clocking around 92,000 kilometers. The vehicle exhibits noticeable engine surging when operating at normal temperature and steady throttle input—specifically around 1200 RPM. When the driver suddenly increases throttle, the engine momentarily loses power, then recovers after a few seconds. Holding the throttle steady causes the engine to enter a 'hunting' state, where it repeatedly fluctuates in speed. The issue is particularly dangerous when starting from traffic lights—initially the engine stalls, and only regains power when the driver pumps the accelerator. This makes merging into traffic extremely risky. I have been resetting the P0171 code each time, but the vehicle consistently returns with a P0171 (Lean Air Fuel Mixture) code while driving. I recently ordered a fuel pressure tester to evaluate fuel rail pressure and am currently investigating potential vacuum leaks. Any advice on diagnosing or resolving this issue would be greatly appreciated—especially in relation to the P0171/P0172 fault codes, engine surging behavior, and possible root causes such as fuel delivery or oxygen sensor performance.

Related fault codes
P0172
Comments (11)
Anonymous 2007-07-13 06:57

This post is a bit confusing—could you confirm whether it's P0171 or P0172? These codes are not identical and have different implications.

Anonymous 2007-07-13 07:39

Could you clarify which specific code you're currently seeing and what diagnostic steps you've taken so far?

Anonymous 2007-07-13 09:10

It's a P0171 code. Sorry for the confusion—this was late at night, and I missed clarifying earlier!

Anonymous 2007-07-13 09:22

Possible causes include low fuel pressure or an oxygen sensor that is not properly detecting air-fuel ratios, leading to a lean condition.

Anonymous 2007-07-13 11:22

I recently replaced both the upstream and downstream oxygen sensors. I suspect this might have helped with related issues, though it didn't resolve my surging problem entirely.

Anonymous 2007-07-13 11:47

Could you specify which codes you're seeing and what brand or model of oxygen sensors were installed?

Anonymous 2007-07-13 11:52

The first step should be checking fuel pressure and looking for vacuum leaks—both are common causes of lean conditions and engine surging in older vehicles like this one.

Anonymous 2007-07-13 13:05

In my case, I previously had a P0138 code (O2 sensor circuit malfunction), so I replaced both O2 sensors as part of a broader fix. It didn't fully resolve the issue, but it was worth trying.

Anonymous 2007-07-13 13:08

I'm waiting for my fuel pressure testing kit to arrive. In the meantime, I've rigged up a vacuum hose from the engine bay into the cabin so I can monitor real-time vacuum fluctuations during surging events—this will help me provide more detailed data when discussing symptoms.

Anonymous 2007-07-13 19:45

Why are you monitoring vacuum? What brand of O2 sensors are you using?

Anonymous 2007-07-14 10:29

Monitoring actual vacuum variations during surging is critical. This data will help me accurately describe the engine behavior when discussing symptoms with others, and it may reveal patterns linked to fuel delivery or sensor feedback.