Audi A4 2.6 idle and throttle control issues
Discussion
Hi guys,
Quicker summary at the bottom of this post.
Looking for the fruits of your collective knowledge here. My car's a 1996 A4 SE, with the 2.6 12v engine. She drove perfectly on Tuesday night, and I parked up until Saturday. Come Saturday morning, the engine was very sluggish to turn over (I was actually in doubt that it was going to start at all), and then fired up to hold about 1800rpm. Normal idle speed is 850rpm or so, if very cold she might start as high as 1300, so this was very worrying. Then the revs started hunting repeatedly and quickly from 1500-1800, cycling up and down maybe once a second. I shut down, restarted, exactly the same.
I didn't have much choice but to drive it to work like that, and noticed doing that that the throttle was also being released very slowly - I'd back off, the car would keep the power on for maybe three seconds then remove the throttle. Also saw that, while the analogue clock was still correct, the digital trip meter had reset as it does when the battery's disconnected.
When I got to work, I tested the battery, found it pretty knackered, replaced it. Started up, exactly the same, repeatedly hunting.
A quick look around on the web said that disconnecting the battery for a half-hour can clear the ECU's memory for throttle and so on, not sure if this has any effect on my car but I disconnected for two hours and fired her up again. Same. There's a throttle calibration method, so I tried that although again, I don't know if it works for my car (key to ignition on, throttle pedal down for five seconds, key off, release throttle, leave key in but off for two minutes) but this made no difference either.
There are two breather pipes running from each cylinder head to the inlet just before the throttle body, and these were full of a yellow gunky crap. Took those and all the inlet components up to the throttle body, blasted them all out clean and dried them, still no better. In fact, the revs weren't hunting up and down when I tried it just now, but the throttle was still taking ages to close - if I blip the revs up to 3k or whatever, it'll sit exactly there when I let off for four or five seconds before dropping down to a too-fast idle around 1400rpm.
The throttle is cable-operated, but seems to move perfectly freely by looking at how the throttle body and all the linkages move when someone works the pedal. No pipes look to be broken or leaking, though I might not have been able to check them all. I'm fresh out of ideas as to what could be causing this..
So, summary - car starts up at 1800rpm, settles to very fast idle of 1400rpm, it takes five seconds to release any applied throttle, randomly starts hunting quickly between 1400-1800rpm. Throttle cable appears to move freely and allows both fully open and fully closed.
Anyone got any ideas?
Quicker summary at the bottom of this post.
Looking for the fruits of your collective knowledge here. My car's a 1996 A4 SE, with the 2.6 12v engine. She drove perfectly on Tuesday night, and I parked up until Saturday. Come Saturday morning, the engine was very sluggish to turn over (I was actually in doubt that it was going to start at all), and then fired up to hold about 1800rpm. Normal idle speed is 850rpm or so, if very cold she might start as high as 1300, so this was very worrying. Then the revs started hunting repeatedly and quickly from 1500-1800, cycling up and down maybe once a second. I shut down, restarted, exactly the same.
I didn't have much choice but to drive it to work like that, and noticed doing that that the throttle was also being released very slowly - I'd back off, the car would keep the power on for maybe three seconds then remove the throttle. Also saw that, while the analogue clock was still correct, the digital trip meter had reset as it does when the battery's disconnected.
When I got to work, I tested the battery, found it pretty knackered, replaced it. Started up, exactly the same, repeatedly hunting.
A quick look around on the web said that disconnecting the battery for a half-hour can clear the ECU's memory for throttle and so on, not sure if this has any effect on my car but I disconnected for two hours and fired her up again. Same. There's a throttle calibration method, so I tried that although again, I don't know if it works for my car (key to ignition on, throttle pedal down for five seconds, key off, release throttle, leave key in but off for two minutes) but this made no difference either.
There are two breather pipes running from each cylinder head to the inlet just before the throttle body, and these were full of a yellow gunky crap. Took those and all the inlet components up to the throttle body, blasted them all out clean and dried them, still no better. In fact, the revs weren't hunting up and down when I tried it just now, but the throttle was still taking ages to close - if I blip the revs up to 3k or whatever, it'll sit exactly there when I let off for four or five seconds before dropping down to a too-fast idle around 1400rpm.
The throttle is cable-operated, but seems to move perfectly freely by looking at how the throttle body and all the linkages move when someone works the pedal. No pipes look to be broken or leaking, though I might not have been able to check them all. I'm fresh out of ideas as to what could be causing this..
So, summary - car starts up at 1800rpm, settles to very fast idle of 1400rpm, it takes five seconds to release any applied throttle, randomly starts hunting quickly between 1400-1800rpm. Throttle cable appears to move freely and allows both fully open and fully closed.
Anyone got any ideas?
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