2007 Suzuki Swift+ P0301 Shaking at Idle

[Arrakark]

Hello,

Let me tell you the story of my latest project car, a 2007 Suzuki Swift+. I bought this car literally less than a week ago for $500 CAD ($411 USD at time of writing). It has 251,074 km on it. Previous owner said that the battery was new, had new spark plugs, new oil filter and recent oil change. Everything else works.





View photo album here.

The main complaint was that the "car shakes while driving"...

So I get to the car and inspect it. For +251k km it is actually in immaculate condition. Very very little rust on the underside. I suspect it was stored in a garage. Maybe even driven indoors only. Only visible rust was on the windshield wipers of all places, and some peeling paint.

Suspension looks great. Tires have been replaced clearly and have tons of tread and no unsymmetric wear. I don't understand how this car can shake while driving. If it does, it has to be not shaking very much.

I go to start the car and.... the car start shaking. Best described as a "powerful massage chair". What they wrote in the ad was totally wrong, the car shakes at idle.

I decide that I hate myself and decide to purchase it.

On the drive home I burn through half a tank of gas. Surprisingly the temperature gauge maxes out at about half temp. I notice that the shaking is most noticeable at a stop. It generally goes away after about 10km/h or higher, and comes back at around 80km/h, but only when I give it gas. It doesn't shake much at 80km/h if I don't give it much gas. Generally very slow to accelerate, especially at higher speeds or when going up a hill. Very fun to drive though.

In short, the symptoms are:

• Car shakes a lot on idle and low speeds
• Car also shakes while accelerating at higher speeds
• Smell of gasoline from exhaust
• Terrible fuel efficiency
• Check engine light
• Start idling at 1k rpm, drops down to 750 shortly after
• Idle is smooth (does not fluctuate in rpm) and does not change much after initial startup

First thing I do is plug in an OBD2 reader (should have brought it to before I bought the car). Pulls up two codes:

• P0131: O2 Sensor Circuit Low Voltage (Bank 1, Sensor 1) (Upstream sensor)
• P0301: Cylinder 1 Misfire Detected

Focusing on the misfire, I replace the spark plugs. The spark plugs are worn (not new at all). Cylinder 1 spark plug is more charred than the rest of the plugs. Doesn't help.

I replace the ignition wires because I'm a dummy and I didn't realize you can test for spark outside the engine. But then again, sparks act differently under pressure and maybe it's a good time to change them anyways. No change.

I replace the ignition coil pack with a new one. No change.



I figure it must be the injectors. I take the injectors out along with the pipe that spread the fuel to them. I clean them up and attach a can of compressed carb cleaner to the fuel input. While pressing the button on the carb cleaner I apply 12V to each injector and collect the cleaner in a cup. This way I clean the injectors and verify that each of the four holes of each injector is not clogged.



I place the injectors back and verify their operation by placing a screwdriver to them and my ear. All of the injectors work.

Hmm.. okay. We have fuel, we have spark, do we have air? I decide to do a compression test:

• Cylinder 1: 175psi
• Cylinder 2: 185psi
• Cylinder 3: 200psi
• Cylinder 4: 185psi

Hmm. Not good but not terrible either. I do this for dry values only. Technically, all values are within 15% of the max, which I read somewhere is okay.

I read online that a faulty O2 sensor can cause this. I replace it for $120. Oof. P0131 goes away and I confirm that the O2 sensor outputs 0.1-0.3V roughly depending on how I drive. I thought I had an issue with the harness after I replaced the sensor because the ECM kept reading 0V. I confirmed with a multi-meter that there were direct connections to the ECM from that sensor (pins 28 and 43 of top connector I believe). I think reseating the connector a couple of times got rid of the issue.

Engine seems to run a bit smoother now at idle. But P0131 still keeps popping up, even after I clear it. Fuel consumption did not go down either.

I do a vacuum leak test with propane. I check the intake (I wrapped intake hose with duct tape because it had cracks in it). Can't find anything...

To summarize, here is what I did:

• Replaced spark plugs
• Replaced ignition wires
• Replaced ignition coil pack
• Replaced O2 sensor (make it run a bit smoother and got rid of P0131)
• Did a compression test
• Vacuum leak with propane
• Reset the ECM and codes several times after each change

Unfortunately, now I'm a bit stuck. It's clear that cylinder 1 is still misfiring due to shaking and poor fuel economy. Here is some of the symptoms I see now:

• Long term fuel trim is +2.4%
• Short term fuel trim is ~0%-5% depending on acceleration
• Coolant maxes out at 97C
• Timing advance is 0-3 deg on idle, up to 35deg on acceleration
• Averaging 20-30L/100km. Ooof.
• Still hard shaking at idle and P0301 code

I hope you enjoyed listening to my project so far. If you have any suggestions as to what to do next I am all ears!