Occasional RPM surge on stop lights.

[jakeb123]

Among the many issues I have, some are probably related to this.

Basically, I have had an RPM surge once in a while, we are talking about 300-400RPM surge only when on idle.
I recently managed to replicate the problem 100% of the times, by quickly and I mean very quickly pressing the gas pedal when idling and letting it go, my foot is off the gas pedal before the RPM even manages to climb.

What happens then? Weird stuff. The car remains idling for a second or two to 1000RPM, then it rapidly drops to 500 or even 300, the engine itself is on the brink of shutting off and then it recovers.
But dont take my words for it, I have a video

I have an S40 2002, 1.6 petrol engine, naturally aspirated, manual gearbox. I have read about possible throttle body failures, but this concerns the electronic ones while mine is a regular one and it honestly seems fine.
You might have noticed the CEL, thats a P420 code related to the oxygen sensor, but they are working fine, I think it's related to this issue.

[E Showell]

I drove a manual '98 V70 with the exact same issue for probably close to 10 years. In that time I put 270,000 miles on it and replaced the engine. Engine replacement did not cure the issue, so you can breathe a sigh of relief that it is not a bum engine. I never did discover the genesis of the issue. Car still being driven and new owner has put about 25 K miles on it since I sold it. Good luck figuring it out. If you do, please post details here, thanks.

[jakeb123]

Thanks for the reply. The thing is this isn't the only issue. In rare occasions when the car is cold like in the morning, sometimes I get RPM oscillations that jerk the car back and forth when in gear.
And in the rest of the times the car jerks when pressing the gas pedal when it was previously not pressed. The same happens when I let go of the pedal. If I press the gas pedal suddenly, the jerking motion is very noticeable almost like backfire and in a first last night I even popped out of gear due to the jerk, at that time I pressed the gas pedal very fast just like in the video.

As for the RPM surge I am wondering if it's not a valve named Pierburg PA6-GA30,this is a turbo solenoid valve mounted on the radiator and connected to the throttle body, but I don't have turbo.

[alschnertz]

P420 code was a bad cat. on my 2001 S40.

Have you cleaned the throttle body and IAC?

[RickHaleParker]

You might have noticed the CEL, thats a P420 code related to the oxygen sensor, but they are working fine, I think it's related to this issue.

P0420 is not O2 sensor, it is Three-way catalytic converter (TWC) efficiency

Check for Air leaks, Incorrect fuel pressure and Uneven compression.
Any of the three could cause the idle symptoms and code P0420.

Be slow to blame the catalytic converter. Defective Catalytic converters are rare. A lot of people have paid a heavy price for being too quick to blame the Catalytic converter.
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ECM-5A (P0420) Three-way catalytic converter (TWC) efficiency. Faulty signal. Permanent fault

Condition
The catalytic converter's effectiveness is checked once per driving cycle. The control module forces a changed cycling of the front heated oxygen sensor. If the catalytic converter's effectiveness is reduced, the rear heated oxygen sensor's signal will change and trouble code ECM-5A is generated.

Substitute value
None.

Possible source

• Uneven compression.
  Air leakage in the intake system.
  Leakage in the exhaust system.
  Defective fuel pressure.
  Damaged catalytic converter.

Fault symptoms
Poor performance

[jakeb123]

I just want to clarify that I gave you the wrong code. It was P0171. Basically from time to time, I had noticed using my ELM327 dongle that for a short period of time when I start the car, the Short Fuel Trim was +44%.
This might seem like a vacuum leak, you'd be partially correct. All the symptoms point to the same problem in my opinion. Notice in the video how at 1000RPM there is a whistling sound. That is the sound of air entering through seals because of excessive vacuum in the crankcase(yes, excessive vacuum and not pressure). You can read about this issue in my previous thread last paragraph viewtopic.php?t=89862

Since then I managed to partially fix it and even lower my LTFT to 2-3%(the LTFT was lowered when I replaced the tires and evened out the pressure). I found a tiny hose that pushes in to the breatherbox hose and the air filter(after the MAF), it was pushed too far in causing it to touch the inside of the main hose, when the vacuum increased, the tiny hose touched the inside of the breatherbox hose and basically prevented air from being sucked through it, with the vacuum high as it is, it had to enter somehow, which was through any seals it could. I only managed to alleviate the issue, now the whistling is short-lived, as opposed to before where it would start and only stop only when I gave it some gas.

As for compression, in my dry test I managed to get variable readings from some cylinders, some were as low as ~90PSI others as high as ~120. However it is more than possible that I didn't crank enough for some of those cylinders, I was afraid I might kill the battery, even though I disconnected the fuel pump and coil packs. You can see I have a few photos of the same cylinder and different readings, some higher than the previous.

I do experience lower performance, I've had occasions where on an uphill, even in first gear the car would struggle with the hill where other cars would not. But this was one event, more common were other uphills where I had to drive in second gear, where others would drive in at least 3rd or 4th. Sometimes I suspect the fuel pump as it's likely the original, at 140+k miles, it might be EOL, however a pressure test showed it at 45PSI, though I did not do a leak-down test.
It's also curious is how I always hear a ticking sound from the injectors or valves when passing by other cars, or anything that reflects sound, the ticking increases as I push the gas pedal and stops when I let go.

Sorry if this post is confusing.

[RickHaleParker]

I just want to clarify that I gave you the wrong code. It was P0171.

ECM-25 (P0171) Long-term fuel trim. Rich. Intermittent fault

Diagnostic trouble code (DTC) information

Condition
The control module receives information from the heated oxygen sensor (HO2S) about fuel / air mixture. If the fuel /air mixture deviates from l=1 the short term fuel trim will compensate for this by adjusting injection time so that l=1 is achieved. When the short-term fuel trim makes an adjustment, the integrator median must be adjusted by the long-term trim. Diagnostic trouble code (DTC) ECM-25 is stored when fuel trim has reached an upper limit (lean limit) or a lower limit (rich limit).

Substitute value
Fuel trim is disabled.

Possible source
Rich limit:

• High fuel pressure.
  Leaking injectors.
  Contaminated oil.
  Oil level too high.

Lean limit:

• Low fuel pressure.
  Air leakage in the fuel injection system.
  Leakage in the exhaust system.

Fault symptoms
None.

[alschnertz]

Be slow to blame the catalytic converter. Defective Catalytic converters are rare. A lot of people have paid a heavy price for being too quick to blame the Catalytic converter.

Couldn't agree more.
I did a lot of diagnosis before replacing the cat. on my 255K mile '01.
FWIW, the Bosal replacement didn't fit.
Magnaflow fit like a factory part ($350+/-) and haven't had the P0420 reappear over the last 5K miles.

[jakeb123]

Humor me a bit. Is it possible the issue in the video is caused by a faulty Vacuum Purge Valve or a faulty EVAP canister or really a fault in the EVAP system?

[Mykyta]

Hey, have you solved the issue?