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I purchased my Astra about a year ago. I bought it when it had 110,000KMs, and it is now sitting around 125,000KM.
I’ve had the same issue with the car since I purchased it. The car idles a bit rougher than I would think for a small 1.8, where you can feel the engine throughout the car. The RPMs are constantly “hunting” it seem. It doesn’t matter if the car is idling, or sitting at 3K on the highway, you’ll see the needle move up and down. Something which I think is related is the intermittent lack of power. Sometimes it’ll just fall on its face and barely move, other times, it’ll go zoom zoom when you put your foot down. There doesn’t seem to be a rhyme or reason, whether the engine is hot, or cold, or the ambient temp is -20 or +20.
I have changed quite literally everything on this car trying to chase this problem. Besides the generic oil changes and filters, I’ve done; 02 sensors, throttle body, valve cover(s), intake manifold, spark plugs (multiple), coil pack, VVT solenoids, cam sensors, complete timing including VVT sprockets, quite literally everything.
Most would say the issue isn’t that big of a deal, but having a car this small, and a 5 speed, it would be nice for it to be fun to drive.
Measure the fuel pressure at the rail and the throttle position sensor along with the RPM of the engine in real time. All through live monitoring and recording data of a decent scanner.
Can you feel the RPMs going up and down or is it only the needle?.
Falling flat on his face often is an air to fuel mix issue.
What do your long-term and short-term fuel terms look like?
Are you using stock plugs and a stock O2 sensor in the front?
Any modifications to the exhaust?
Couldn't find anywhere in your description it was a 5 speed. Anything else we need to know? Not sarcastic
Measure the fuel pressure at the rail and the throttle position sensor along with the RPM of the engine in real time. All through live monitoring and recording data of a decent scanner.
Can you feel the RPMs going up and down or is it only the needle?.
Falling flat on his face often is an air to fuel mix issue.
What do your long-term and short-term fuel terms look like?
Are you using stock plugs and a stock O2 sensor in the front?
Any modifications to the exhaust?
Couldn't find anywhere in your description it was a 5 speed. Anything else we need to know? Not sarcastic
No modifications in the exhaust, and it has been pressure tested for leaks. Stock spark plugs gapped properly as well. I believe I’ve been through 4 different kinds to see if there was any change - there was not. Yes, both 02 sensors are genuine, no cheap parts anywhere.
Although it’s minor, you can definitely feel the RPMs change as well. I believe it is something like + or - 40/50 RPMs when the needle is going up or down. I’ll see if I can attach a brief video! Keep in mind that it will do this at idle, or even cruising at 100KPH.
When I changed the intake manifold, the new assembly came with new injectors, fuel rail, and everything else attached to the intake manifold.
Also the fuel air ratio is always sitting at 14.64. Now, my scanner ain’t that advanced, but given that I’ve had multiple shops look at it, no one can figure it out. My main shop even said they have no idea and don’t even know where to look.
Measure the fuel pressure at the rail and the throttle position sensor along with the RPM of the engine in real time. All through live monitoring and recording data of a decent scanner.
Can you feel the RPMs going up and down or is it only the needle?.
Falling flat on his face often is an air to fuel mix issue.
What do your long-term and short-term fuel terms look like?
Are you using stock plugs and a stock O2 sensor in the front?
Any modifications to the exhaust?
Couldn't find anywhere in your description it was a 5 speed. Anything else we need to know? Not sarcastic
How about monitoring the injector pulse width with rpm?
How fast is this oscillation in RPM? Once per second, once every 5 seconds five times a second? If it's really fast I don't think you would be able to see the pulse width changing even if it was. Actually I don't know on what frequency that is adjusted.
I'm going to question whether you can hear or feel a 40 RPM change on the highway.. at idle, sure.
There has to be filtering of the O2 signal has part of the control loop feedback to the injectors. I don't know at what frequency those values are updated to calculate aired a fuel ratio and make adjustments to the injector pulse width. You said your air fuel ratio is 14.6. how stable is that? My first guess would be that would have her signal is coming out of the O2 sensor in the front is not getting sufficiently filtered and/or averaged before it goes to the PCM or once it reaches the PCM. So you have a slow oscillation in the fuel to air ratio and therefore a slow oscillation in the pulse width to the injectors. It never settles down because it can't.
Have you checked any of the Astra forums?
I'm shooting from the hip. Try the opel Astra forums across the pond. It may just be a crude control loop. But you can't be the only one whose vehicle does this
08 Astra XR 5 Speed
