Rough idle on low speed

Hello everyone,

I'll try to make my story short
After doing a silly mistake on my timing belt change, I blew out my head. So I got a "new" rebuilt one, installed a new timing belt and new injectors, 'cause the old ones were all plugged out. I had the new injectors checked before installing just to be sure they were ok.

The motor now starts easier than before, runs well and idle well, but only when the car is stationary ! When the car is moving slowly, and I let the motor idle, it is rather rough !! And as soon as the car comes to a complete stop, idle gets back to normal and very regular. No codes in OBD.
Anyone has any idea were I could check to pinpoint the source of this problem ?

Also, I don't know if it's related, but I wanted to reset the readiness codes by doing the procedure written in the big red book. All codes resetted to 0 except bit 4, which stayed at 1 ! What does that bit stands for ? Any tricks so that it would reset ? Maybe I'm doing something wrong in the reset procedure ? I'm doing the on-road reset procedure, since I didn't figure out how to reset those codes with Vag-Com.

Dominic

check your injection quantity

Hi !

My idle is at 903 rpm, and the computer shows 0.20l/h !

I believe the injection quantity should be between 3-6 mg/stroke. I just had a guy check mine yesterday and I think that's what he said the range should be.

I know mine was out of spec at 1.4 mg/st

Hi,

Did some other tests, my injection quantity is at 1.4 mg/R, like yours, and I think it's ok since the motor runs well at 903 RPM idle. But I noticed that when it's knocking at my idle while cruising at low speed, the injection quantity gets below the 1.4... It varies between 1.2 and 0.0 ! And when I see the number rise up again at 1.4 or more, it stops ! So could it be that the computer needs a setup ?

If you're coasting in gear I would suspect that your iq would be 0. Try dropping your IQ value by 100 and see what it does. thats all it took on mine. If it helps but doesnt completely get rid of the rough idling drop it another 100. I think the iq looks at the wheel speed sensor and once the computer sees that the car has stopped it uses a different value. This is just speculation but mine would idle rough when coasting out of gear and as soon as my speed fell below a certain speed it would idle normally.

Hi,

Did some other tests, my injection quantity is at 1.4 mg/R, like yours, and I think it's ok since the motor runs well at 903 RPM idle. But I noticed that when it's knocking at my idle while cruising at low speed, the injection quantity gets below the 1.4... It varies between 1.2 and 0.0 ! And when I see the number rise up again at 1.4 or more, it stops ! So could it be that the computer needs a setup ?

Click to expand...

No. Changing the IQ does not change the idle speed. Adapt the IQ (search the site for the procedure) to something above 3.0, and it should be fine...

This issue is called "Slow Down Shudder" and is well documented here. It is a common problem. The fix is to raise the IQ.

moondawg

Hello again,

I did change the injected quantity to 3mg/R by setting the code 01 to 32668 ! Shudder is now very less noticeable, almost none... I notice it more now, since I heard its worst... I guess that I never noticed before, because you could mistaken it for a brake shudder.

Also, I noticed that when there is more electric draw, the motor could shake at idle ! I'm surprise, because most of the injection system is mechanic !