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beyerdynamic
20-09-2007, 03:19 PM
Hope someone can shed some light on this one,the audi in question is a coupe 1993 16v with engine code ACE,the prob.is as follows:- engine will start as normal from cold and idle at 1100-1200 rpm then drop down slightly when warmed up,the problem starts when it has fully warm up to operating temp.,the engine revs. flutuate slowly climbing to 1900 rpm then there is a blip where it will decrease by 200 rpm then do it again,sometimes the revs build up to over 2000,before returning back down to between 1100 and 1500 rpm then flutuate again,i have changed the isv to no avail and whilst the engine was reving up disconected the isv elec. plug but nothing happened,the revs carried on flutuating have taken off the throttle body and gave it a good clean with carb cleaner;still the same,my instints say that there might b a prob. with the fuel pressure regulator,though i`m not too sure,all the plugs and dist. cap and rotor arm are nearly new,also when driving at slow speed and part throttle there is a big flat spot when the throttle is pushed any further,almost feels like its going to back fire but will then pick up again ,would be glad of any ideas

scotty33
21-09-2007, 12:11 AM
I once caused similar symptoms to this on an 8v passat. I was trying to cure a low idle/stalling problem and I adjusted the throttle stop screw so that the throttle would be slightly more open. The idle was all over the place after this. I now know this screwed up the idle switch operation.
You could try adjusting yours, just make a note of where you started?

beyerdynamic
21-09-2007, 10:15 AM
Thanks will give it a go,whilst i`m doing that i`ll check over every thing to make sure there are no leaks in any hoses which might cause the eractic idle

Crasher
21-09-2007, 01:28 PM
Do not adjust the throttle stop screw, that isn't permitted, is a bodge, and will cause fault code 00516 and 00533, the VAG quote for this being “Limiting screw is set at factory and is not to be altered. If screw has been turned inadvertently, throttle valve unit must be replaced” and that parts costs £784.04. Get a fault code scan done to see if you have a faulty coolant temp sender. You will have code 01257 now you have run the engine with the ISV unplugged.

beyerdynamic
21-09-2007, 04:05 PM
Thanks for that advice,have discovered that isv valve isn`t working as it should be and was stuck in one position causing the fast idling,a tap with a screwdriver fixed that one but a new valve is on the way so that should fix that,thanks for the advice will update when the valve is on the car.

scotty33
23-09-2007, 04:08 PM
Do not adjust the throttle stop screw, that isn't permitted, is a bodge, and will cause fault code 00516 and 00533, the VAG quote for this being “Limiting screw is set at factory and is not to be altered. If screw has been turned inadvertently, throttle valve unit must be replaced” and that parts costs £784.04. Get a fault code scan done to see if you have a faulty coolant temp sender. You will have code 01257 now you have run the engine with the ISV unplugged.
I agree with this to an extent, it is not a good idea to adjust the screw in principle. I should not have advised doing it, but the symptoms described matched. In practice I can't see what harm would be done, if it is noted how far it is altered and then returned to the original position? I had no further problems with my passat, once I repositioned the throttle stop and adjusted the Idle air screw instead. (which I should have done in the first place)

Back on track, I really can't see how another ISV will help. If the idle is varying, with the ISV unplugged, then the ISV can't be at fault.

I can see that the ECU temp sender could cause the car to run rich if faulty.
Getting the codes read is the ideal thing to do, the problem is the ACE is a pig to get codes out of and usually means a trip to the dealers. You should be able to read different resistances (ohms) on a meter, between a hot and cold engine.
I would also test the lambda probe function. It has three wires, two are usually white and the third may be black? - this is the signal wire. If you get the car warmed up, and leave the connector plugged into the wiring harness, you need to get a multimeter set to volts or millivolts, and put the positive lead probe into the back of the signal wire wiring connector, the negative lead probe needs to go to earth. A healthy lambda sensor gives a signal of 0.2v approx rises to 0.9 volts approx falls to 0.2v etc once per second. if it is slow or not averaging 0.5v it needs to be replaced.
When the car is warming up, the lambda is not used to control the mixture, when the ecu coolant sensor shows that the engine is warmed up, the lambda comes into effect. On the ACE engine, it controls an actuator on the fuel metering head, I guess it affects fuel pressure? the fuel flow varies with airflow.

As I understand it, unplugging the lambda probe would cause the ECU to substitute a default value, (limp mode), which apparently disables the actuator. This might be a useful test, if you don't have a meter available.

Crasher, I don't want to annoy you, I will probably need your advice anytime soon! I would expect you to give accurate advice, I will only advise differently, if I know of a cheaper way:beerchug:
The idea of a trip to the dealers makes my wallet go :1zhelp:

Crasher
23-09-2007, 06:12 PM
You haven’t annoyed me old boy, different mechanics have different opinions. The problem with these early Audis is not everyone has the 2x2 adapter cable for code reading and some of them refuse to talk to VAG-COM which is why I still have my old Omitec tucked away for when it is needed.

beyerdynamic
27-09-2007, 10:45 PM
I agree with this to an extent, it is not a good idea to adjust the screw in principle. I should not have advised doing it, but the symptoms described matched. In practice I can't see what harm would be done, if it is noted how far it is altered and then returned to the original position? I had no further problems with my passat, once I repositioned the throttle stop and adjusted the Idle air screw instead. (which I should have done in the first place)

Back on track, I really can't see how another ISV will help. If the idle is varying, with the ISV unplugged, then the ISV can't be at fault.

I can see that the ECU temp sender could cause the car to run rich if faulty.
Getting the codes read is the ideal thing to do, the problem is the ACE is a pig to get codes out of and usually means a trip to the dealers. You should be able to read different resistances (ohms) on a meter, between a hot and cold engine.
I would also test the lambda probe function. It has three wires, two are usually white and the third may be black? - this is the signal wire. If you get the car warmed up, and leave the connector plugged into the wiring harness, you need to get a multimeter set to volts or millivolts, and put the positive lead probe into the back of the signal wire wiring connector, the negative lead probe needs to go to earth. A healthy lambda sensor gives a signal of 0.2v approx rises to 0.9 volts approx falls to 0.2v etc once per second. if it is slow or not averaging 0.5v it needs to be replaced.
When the car is warming up, the lambda is not used to control the mixture, when the ecu coolant sensor shows that the engine is warmed up, the lambda comes into effect. On the ACE engine, it controls an actuator on the fuel metering head, I guess it affects fuel pressure? the fuel flow varies with airflow.

As I understand it, unplugging the lambda probe would cause the ECU to substitute a default value, (limp mode), which apparently disables the actuator. This might be a useful test, if you don't have a meter available.

Crasher, I don't want to annoy you, I will probably need your advice anytime soon! I would expect you to give accurate advice, I will only advise differently, if I know of a cheaper way:beerchug:
The idea of a trip to the dealers makes my wallet go :1zhelp:

problem cured now,changed isv valve idle is now dead steady at 920-950 rpm,will keep you posted if prob. comes back,thanks for the advice.