Audi 80 splutters after cold start?

Coolant Temperature Sensor for the Fuel Injection Loose clamps on the Intake Manifold Boot. Bad Fuel Injector Seals allowing air by them until they warm up and expand. Possibly a fuel pressure problem. To name a few possibilities. ;-)

Did it have this problem BEFORE the full service?

Thanks Dave, yes according to the owner it has been a bit stuttery on initial start off for some time. I checked the ecu temp sensor which is giving normal readings (300ohm hot & 3000 cold) But I did notice there is no voltage at the Inlet manifold heater terminal. Can anyone confirm if this should show battery voltage on ignition? I'm not sure how this operates, if it only comes on under a certain temp or should be on permanently.

Thermo time switch will only apply power to the cold start injector under about 7 deg C.

Tim. .

I'm not sure this baby has a cold start injector, in fact it doesn't seem to have much at all compared to engine pics I've seen of other Audi 80's. It's the 2.0 SPI Mono-Motronic and it all seems very sparse underneath. I've now had a look on Autodata and the only engine temperature related items I can see on this model are the coolant temp sensor (one for ecu & one for gauge), Intake air temp, manifold heater & O2 heater.

My 5th injector is controlled both by a thermo switch and by the ECU on cold start for warm-up enrichment. But since the OP said he doesnt have a 5th inj. I guess it makes no odds.

OK the cold start injector is either not there or very hidden, but I think the engine starts fine. I also understand that the engine runs fine after it warms up.

Power to the 02 sensor might be from the fuel pump circuit. Fuel Pump off = 02 power off. Not sure on this though!

Now the engine could be running either very lean or very rich and a quick smell of the exhaust will tell you if it is running rich when you first start it. If it is rich then it could have a weak spark and the plugs are fouling out. When it is at normal operating temperature has the CO been adjusted? You could try adjusting the CO bolt 1/2 turn CW to richen mixture and see if that makes a difference.

I still think it could be a vacuum leak(s) at the intake manifold boot or the injector seals which would cause a lean condition until the rubber warms up and expands.

Now I did not mention that the timing could be off too. Timing belt and/or ignition. I guess I would start at the basics and check the timing belt, ignition components including distributor timing, fuel delivery, etc.

Did you do the major engine service?

The local garage who are generally very good did the yearly service (filters, oil & plugs) but I also replaced the dis cap & rotor arm and a bottle of petrol treatment in the tank. I saw the old plugs and they all look ok with no obvious signs of incorect mixture and it also passed it's yearly MoT emissions test with no problem. I think CO is all controlled by the ecu. Owner says it drives smoother but still has that initial hickup from a cold start. I'm tending to lean towards no power going to the inlet manifold pre-heater being the problem. Here's a pic I found on a German parts site:

I found this posted in reply to someone with a similar inlet pre-heater on their VW fitted with carburettor & manual choke. "...The 'hedgehog' as it is affectionately known prevent vaporised fuel from condensing on the inside of the inlet manifold at low temperatures. This reduces the amount of choke needed, improves emissions and gives better drivability when the engine is cold..." The Audi has SPi and no choke but if the inlet heater works on the same principle could this be the cause of the stumble on cold starts?

Ahhh, not a K /KE jet then!

Scrap all the above..

Either you have a failed intake heater, or the injector is gummy and sticking. The latter would be my bet.

Get it in an ultrasonic bath for a good clean to start with.

Tim. .

The more I read the more I'm convinced it is the manifold heater "hedgehog". There is no voltage showing at the wire connecting to the heater plug. According to Autodata there should be battery voltage on ignition but there isn't. However, the volt meter does detect a trickle for a split second as I switch on ignition so I'm guessing that the wiring is in order and the problem is the heater relay. Anyone know which relay it is and is there a way to test it?

I was under the impression air intake heaters were for periods of extended idling, not for cold starts.

why not power it with a jumper wire and see if that makes it run better?

No, Single pointers and even some SU equipped vintage tack (Rover R, O, S series motors for example) with hedgehogs run them ALL the time- they are a PTC which means they self regulate and maintain the same temp pretty much under all conditions.

Its there to make up for the poor atomisation of the fuel supply system.

Tim..