Hello everyone,
I have been using Sprocket's excellent guides for years in sorting out problems, also the posts by many users such as FlyingScott, DaveRob to name but two but I have come up against this problem for which I find I need to actually make a post about!
This is a bit rambling but please bear with me - the questions are at the end!
I have had fast idle problems in the past in the past, usually cured by changing the vac hoses and it started again recently but seemed to improve after doing some servicing work, - new steady bushes top and bottom, new air filter, dizzy cap, rotor arm, spark plugs water pump, water pump pulley and alternator. Also adjusted the valve clearances, flushed the cooling system and fitted a new oil pressure sender. When the alternator failed it did so very suddenly, I was driving home and switching on the lights I noticed the dash illumination to be very dim, this got worse as I continued to the point that the headlights were like candles and the wipers barely made it across the screen unless I turned the mains off and drove on sidelights.
All was fine after this apart from having to adjust the fan belt a couple of times as it stretched and started to slip. The new problems started up whilst the belt was slipping on the way home last week.
Now the idling problem has become worse, revs hanging like the throttle is stuck. Driving the car it revs up to 1800 rpm as the clutch is pushed in, slowly dropping down to 1200 before pulling away again. Lifting he throttle with my foot does nothing and I have pushed on the linkage to the throttle body to confirm the cable isn’t sticking.
It Idles at 1200 rpm from cold as you would expect, but continues through to warm up and stays there until throttle is revved whereupon it will hang around the 1500 - 1800rpm range varying a bit, eventually dropping back to 1200ish. It is not fluctuating rapidly as some posts have mentioned, more just a slight variance of about 50 rpm around the1200 rpm mark or wherever I am holding the revs with the throttle.
During this time the stepper motor is pushing the revs - if you open the throttle the stepper plunger will catch up with the throttle and hold it at 1500 rpm or so for a few seconds as the throttle returns to idle, then it motors back in and the revs settle back to 1200. If I just crack open the throttle the stepper will actually increase the revs to 1500 or so before settling back
At first. If the lights - main beam and spots - were switched on he revs dropped to 900, fairly stable, and then rose again when lights switched off. Battery voltage was low possibly due to the slipping fan belt, I have charged it now and the lights only bring he idle revs down a bit. The ‘sticking’ is the same however.
Investigations so far:
Fuel trap needed changing - there was some fuel in the lines between the manifold and the trap but also in the one between the trap and the ECU. There was also a bit if brown residue in the ECU outlet when I took it out to have a look so I dried to out on a radiator as suggested.
Vac hoses themselves were fine but I changed them anyway though it made no difference.
Temp gauge reads mid way on the white tick as it always has done, occasionally raises up to the black line in traffic.
I have adjusted the throttle cable and set it by indexing the stepper motor as in the manual. The stepper motor does the usual thing of indexing as you switch off too.
Plugs are new (100 miles or so) and still fairly clean but there is a small amount of carbon build up around the edge so it appears to be running a bit rich.
Fitted a new air inlet temp sensor but this made no difference either
Rambling over, now the questions!
Now I have done all the easy to get to stuff I am turning my attention to the Coolant temp sensor, Lambda sensor or stepper motor...
From my description does it seem that the stepper is operating correctly?
With the temp gauge behaving correctly does this mean the CTS is ok?
As I have no hesitation, misfiring or any other symptoms of poor running can I assume the Lambda sensor is ok?
Does any of this give an indication of what to try first?
Cheers
Robbie