Hi folks.
Can i ask, if the idle control valve failed will this prevent the car from starting?
MY87S4

Thank you
Martin.

 

The ISV in its native position is designed with an open aperture designed to support the stock idle speed when the engine is hot and the ac is not operated. Thus it should work almost the same as when it is functional. What I found is that on initial start you may need to fether the throttle pedal a bit to get it started. If the thing is dead switch the ac on and the motor will die.

 

Thanks Fred.
My S4 has fuel in the injectors and sparks but will not start. I was wondering if there could be air starvation?

Martin.

 

Martin,

If you have fuel and sparks it should fire up so one of those two has to be suspect unless something really oddball has blocked off the air. Perhaps you can describe how you ascertained your conclusions. You can also try starting with the throttle partially open.

 

Hi Fred.
I was having idle surging so decided to replace the idle control valve and do an intake refresh. I bought the control valve of ebay. I was assured it was for an S4, but when it arrived it was smaller than the original Bosch unit. After putting it back together it no longer starts. I have tried new leads, coil, amplifiers, spark plugs even tried alternative LH and EZK computers.
This is why i am thinking the idle control valve may be responsible for the car not starting.

Martin.

 

Martin - I doubt it would stop the car starting. It would have to be a major failure to do that. They are normally pretty reliable but the rotating valve can get clogged with carbon.

 

Clean the original with brake cleaner and put it back.

 

Martin,

There is an after market ISV available that works perfectly, Roger sells them [so you know it is good] but as I am aware they are physically identical to the stock item and who knows, maybe they are OEM units. I have no idea what you have purchased or how it is configured. The unit is pulse width modulated so difficult to test- the PCM controller looks at the rpms whilst the throttle switch is at the idle state and opens/closes the shuttle as needs be.

So, you removed the inlet manifold and changed out the ISV and then the problem started- correct? Did you change out the crank position sensor by any chance? Reason for asking is they have the same same 3 pin junior powertimer connector as the idle switch, similar length and location and are easily confused- mix them up and your engine is not going to start. You fitted new leads- are you sure they are assigned correctly- unlikely you would get them all wrong but..? They will spark but incorrect timing of course.

 

Hi Fred.
The problem first started when the weather became colder here in Scotland. I would try and start the car in the morning and it would just crank. I would then try to start it in the afternoon and it started albeit quite lumpy for about 30seconds, probably due to excess fuel, but then drove perfectly. It was suggested the temp2 sensor was faulty so i changed it for a new one but the same symptoms persisted. Then i read somewhere that the isv could give rise to poor starting if faulty, hence the intake re-fresh.
I am not a mechanic by any means but get by. I have a new cps but the weather has not been the best to attempt to change it on my drive way. I thought if the cps was faulty i would not get a spark?
Kind regards.
Martin.

 

Thanks for that Roger. I will try that.
Kind regards.
Martin.

 

Martin,

When removing the inlet manifold the TPS has to be disconnected. When doing the inlet manifold it is common to clean the earth connection s and as I recall undoing the CPS connector to help make room is part of the procedure. /if you did not undo that connector then nothing could have changed in that respect but as you can see from the queries, understanding the history and what was done is a critical part of the analysis.

At this time of year on cold starts it is unlikely you are going to over fuel. If after trying to start and having got nowhere have you pulled a plug to test for fuel presence?

 

Fred.
I can confirm the plugs are wet with fuel. The cps has not been disconnected. I loosened the nut to the fuel rail and cranked the car and the fuel pressure was there. I was concerned that perhaps the car wasn't cranking over fast enough to start even though the battery is new, so i have a used starter motor to try.

Martin.

 

A weak starter motor can of course cause slow starting however such condition is probably caused more often than not by a degraded engine harness or more specifically the feeder from the starter motor to the alternator and this problem gets worse in colder weather. Thus if the resistance is too high the voltage drops and at some point the computers can stop working correctly. A new battery helps but at some point you may run into trouble starting if the problem is too much. Slow starts with a new battery is indicative of something not right- whether it is causing your no start I have no idea. Add to that a vehicle standing outside in the street in very damp conditions does not exactly help things. When I replaced my engine harness the engine came out of the starting blocks like Usain Bolt. Take a look at the wiring at the hot post. You will see two cables going towards the front of the car- they will probably have red sheaths. Now look at the rear of the post and it will have one 10mm2 cable leaving the rear side and entering the harness- this will probably look a shabby brown- it should be bright red. Did inside the heat shrink a bit and it may well have insulation that is dropping off- it usually gets worse close to the alternator. Also take a look at the cables leaving the rear of the 14 pin connector- can you see the colours clearly or do they look shabby? The cable leaving terminal 1 is the supposed to be blue and is the exciter for the alternator. Terminal 14 is a 4mm2 yellow cable and that powers the solenoid valve on the starter motor. If the insulation on these cables look poor it is another sign that the harness needs replacing- remember this lot is is 34 years old on an 87 model!

 

Fred.
Thank you for your guidance in giving me more options to check. I will check what you have suggested.
Thanks again.
Martin