7A rough running

Audi Nut Joined: Feb 25, 2010 Posts: 94

Hi All,

I have *finished* the restoration of my Quattro Sport and am sorting a few minor things. However its got a new problem with running rough.

On cold starts its like its not adjusting for being cold - it runs lumpy and idles (or not) at between 400 and 450 rpm. It will attempt to stall a lot for the first few minutes even when you get it up in the rev range.

When hot it seems to run high nearer to 950.

Additionally it will almost rhythimcally surge and bog down when on the motorway - say every second or so it will appear to pep up and then bog down again with the throttle position static.

I am about to change the thermostat and was thinking that the rough cold and warm running problem could be the coolant sensor for the ecu on the back of the head? As I understand it the 02 sensor is not used until the engine is up to temp?

Maybe the random surging could be throttle position sensor?

Thanks in advance guys Smile

Posted: Thu Nov 13, 2014 1:11 pm

The O2 sensor doesn't produce a signal until the exhaust warms up, so I doubt that (or the head coolant sensor) is the problem.

Almost always, I found lumpy idle and surging at low throttle to be due to air leaks in the intake system. The big one from the air cleaner to the MAF/manifold is a common problem. Check underneath.

Sometimes, these problems were caused by a dirty idle stabilisation valve. Mine was the early plunger type and tended to block/get slow with dirt. A clean and recalibration usually fixed it. Have a look at http://www.20v.org/engprob.htm

Worn throttle position sensors usually show themselves as a flat spot when accelerating, but you might check that the 'throttle closed' switch is working properly.

Good luck!
Ian.

Site Moderator Joined: Jan 31, 2003 Posts: 9144

When I had something similar to this it was the throttle body breather hose had a split.

Audi Nut Joined: Feb 25, 2010 Posts: 94

Sorry for the late response. Thanks for the responses.

I have wondered about there being some leak as there is a bit of breather type smell when running - I will have to do some investigation.

I have fitted a bag of snakes manifold and so the metal breather pipe from the crank case is a bit tight on its current route. Was thinking of cutting it to allow better movement and putting a section of rubber in the middle.

The car has had to go back to the tuners so that they can try and get the interface sorted to the new ecu chip - so the car is going to be gone for some time me thinks!

Gavin

Site Moderator Joined: Jan 31, 2003 Posts: 9144

I take it you have the correct heatshield also. You cannot run the tubular manifold without it.

Didn't have any problems with the breather. Is this the one going in to the elephant's trunk hose ?

Audi Nut Joined: Feb 25, 2010 Posts: 94

Yeah I have the correct heat shield for the exhaust manifold.

I had a new 034 breather as well as the BIG MAF kit so there has been a few changes there.....

Site Moderator Joined: Jan 31, 2003 Posts: 9144

all is explained why it doesn't fit.

forgive me for asking but how much are you hoping to gain with the modified maf and what is it costing

Audi Nut Joined: Feb 25, 2010 Posts: 94

The purpose was to remove restriction in the inlet so that I could be certain that this was not holding the car back 5500 and upwards - both now and post and head works.