QuestionHi, I have a 1996 A4 2.8, 5 speed, 150K. Recently, the car has been having starting/idling problems. It cranks fine but will not start. It is very hard to start, especially when it is cold. It sometimes takes 10+ times to get it started, and if it does start it idles horrible and will stall if you take your foot of the gas. I was told it could be a MAF sensor. I took the MAF off and cleaned it properly and still the same problem exists. I have good spark and fuel pressure. I was wondering what could cause my car not to start? Could this be emissions related? Bad sensors?
I used a scan tool to get the trouble codes. They following codes were displayed;
P0102 MAF or VAF, circuit low input
P1504 Idle speed control Auxiliary inputs
P0401 EGR flow insufficient
P0156 02 sensor
Any help would be greatly appreciated.
Answerwhen did the problem start??
was any work carried out prior to the problem??
is it manual/automatic gearbox??
when was service carried out??
were the plugs replaced??
Start simple then move to the less obvious stuff
I would start with the filters, check that they are not clogged, then move to the plugs,even if they are in good condition they can give you alot of insight on the engine, normally they should be either light grey or brownish( depends on the fuel you are using-unleaded fuel usually gives a reddish/brown tan) too white shows the engine is running lean and dark grey or black shows too rich.
If the plugs are too light and you say the fuel pressure is OK then suspect clogged injectors,
while you have the plugs out if possible measure the compression.(low compression can cause hard start problems especially when cold)
now that you've done the basics move on to the other stuff,
1) the airflow cannot be cleaned- the measuring wire is made of platinum and is thinner then a human hair, which makes it very sensitive and fragile, it has a self cleaning function so cleaning should not be necessary and if it is then the only way to sort it out is to replace it, the good news is that you can check it easily,the vehicle has a built in fail safe function called 'limp home mode' which means when a major sensor fails the vehicle dis-regards the signals from said sensor and uses preset values from its memory, to check it disconnect the socket and drive the car, if the problem goes away then the sensor is your culprit.
2) the idle control Auxillary inputs usually points to a clogged or stuck idle circuit, does your vehicle have an accelarator cable or is it the drive by wire kind, after a few miles carbon usually settles on the throttle causing all kinds of problems, remove it and use an industrial solvent like 'ABRO' choke cleaner or similar to clean it out.(please read the instructions properly as this is a very strong solvent) if the vehicle has an accelarator cable then check the function and rectify if there are any faults like sticking or unusual resistance.
3)The EGR function could point to a clogged CAT,, best solution to this is to remove the EGR valve and check it for excessive build up of Carbon,also remove the center silencer (after the manifold and before the silencer box) and check if it is clogged.
4) As for the O2 sensor, I am presuming your vehicle has 4 of these as it is a V6, 2 before the CAT's and 2 after. the usual service interval for these are 2 years ( but thats the law) they usually last abit longer then that. what kind of diagnostic tester are you using?? some scanners can check the O2 values in real time while the engine is running, but if the service interval as passed and in doubt then replace them.
Oh also check the battery. on modern vehicles containing alot of electronics, a bad connection can cause alot of problems!! make sure the terminals are tight and clean, also check the ground points for corrosion and clean them while your at it.
let me know how it goes
