Rough at steady speed

[20Vcqdriver]

Well the cutting out issue might well be resolved, however after a 400mile trip to ADI and back I have discovered that trying to hold a steady speed whether it's 60mph, 70mph I get what is best described as different cylinders cutting out type vibration fairly regularily on the motorway. If I back off so the speed starts to slow or very gently start to accelerate the car returns to its correct smooth running and WOT is OK too. Any ideas? Car will tickover perfectly at 800rpm and despite vibration at steady speed rev counter remains steady as a rock too...

[prj]

Any codes?

Could be an ignition issue, fuel injectors clogged or trigger problem
And it could literally be one of the injectors cutting out as well, or one of the coils.

[20Vcqdriver]

No codes
Mines the single coil 3B. Tested Throttle pot for and sudden jumping but resistance seems to change smoothly

[prj]

I guess you don't have measuring blocks then?
There was a software for 3B that did have them...

The TPS would not affect it anyway, it sounds more like you have an intermittent misfire.
Check the distributor, get some ultrasonic cleaning for your injectors, check the coil...

[20Vcqdriver]

I guess you don't have measuring blocks then?
There was a software for 3B that did have them...

The TPS would not affect it anyway, it sounds more like you have an intermittent misfire.
Check the distributor, get some ultrasonic cleaning for your injectors, check the coil...

Got a spare distributor to try, and an old 7A coil ( would this work). Would IAT sensor affect the running?

[prj]

No, such intermittent faults can only be caused due to severe problems.
IAT, TPS etc are all secondary sensors, which will never cause such behaviour at steady state.

In steady state the fuel mixture is adjusted by the O2 closed loop feedback as well, so the IAT sensor is completely irrelevant here, just as any other temp sensor.

Make sure all the spark leads are okay, take off the spark plugs and inspect them individually, get the injectors cleaned, make sure all grounds are present.

I don't know if 3B will log codes, but AAN will, if you disconnect an injector during operation. The issues that do not show up anywhere are usually spark related.
Another thing that can cause this, is the fuel pump dying or having intermittent power and rail pressure dropping.

[Error404]

I had a similar problem, turned out to be a dodgy injector plug

[20Vcqdriver]

No, such intermittent faults can only be caused due to severe problems.
IAT, TPS etc are all secondary sensors, which will never cause such behaviour at steady state.

In steady state the fuel mixture is adjusted by the O2 closed loop feedback as well, so the IAT sensor is completely irrelevant here, just as any other temp sensor.

Make sure all the spark leads are okay, take off the spark plugs and inspect them individually, get the injectors cleaned, make sure all grounds are present.

I don't know if 3B will log codes, but AAN will, if you disconnect an injector during operation. The issues that do not show up anywhere are usually spark related.
Another thing that can cause this, is the fuel pump dying or having intermittent power and rail pressure dropping.

Would a dodgy lambda cause this due to fact its ok at WOT when its out of circuit though it also clears on more gentle acceleration too when its still in circuit. Will check injectors tomorrow but same issue there too as wouldn't a dodgy injector or dizzy show up at WOT too

[prj]

You can always disconnect it and see if the problem goes away.

[A80Avant]

my part throttle problems almost always went away with either a lamda or a MAF replacement.

[20Vcqdriver]

Does the car run ok without it then? Thought it would end up running rich and 15mpg
Just considered that maybe the methanol/water injection might have fecked it though car still ticks over OK unlike the one I took out last SORN that caused rough tickover and hunting....

[prj]

If your tune is good, then it runs perfectly fine without O2 feedback at 14.7 by itself.

[20Vcqdriver]

OK I'll give that a try, Should be using the car on sunny Friday for earlir start at work so see what happens

[20Vcqdriver]

If your tune is good, then it runs perfectly fine without O2 feedback at 14.7 by itself.

Been too wet to take car out, but decided to do some tests from the warmth of the garage. With the Lambda connected the voltage was jumping about from 0.73 for a few seconds then suddenly dropping off to zero back to 0.3 then back to 0.7 for a few secs then back to zero etc etc. With it disconnected from the ECU wire the output from the lambda remained at a steady 0.8volts for the few minutes I was doing the test. Take it the higher the value the more o2 or weaker the mixture. Strange how it was happy to show a stable output when not connected....

[UrS4boy]

G39 O2 (Lambda) sensor info

Because of the way the voltage was jumping around with the G39 O2 (Lambda) sensor plugged in, and the way it steadied out with it unplugged, I have to think that the issue is with the G39 signal. If, for some reason, it was outputting a varying signal, the ECU would be forced to try to keep up and, as a result, play with the idle fuelling, leading to strange RPMs etc. It is in an unstable loop. Suggest changing the G39.

Here is some G39 info that might (or might not) be useful:

http://forums.quattroworld.com/s4s6/msgs/21012.phtml