Discussion
Yesterday I noticed that off the loud pedal, and out of gear, the engine would idle up to and just under 2k rpm, after five to ten seconds it would eventually settle around 1k. Prior to that and today the engine always idled at just under 1k all of the time.
Intrigued as to what might cause this. It just seemed unnatural to hear the engine at significantly higher revs at idle.
Thoughts welcome.
Intrigued as to what might cause this. It just seemed unnatural to hear the engine at significantly higher revs at idle.
Thoughts welcome.
First check is the stepper motor as this seems to be the cause of most ideling problems, also check that the linkage/cable is not tight somewhere and it is returning to the throttle stop with a nice possitive snap!
Lastly it maybe the movement sensor that I believe is under the dash, there is a modification that can be done others will surely have more detail on this as it is something I have never come across before (thankfully).
However mine does take a second or so to settle down to a 900rpm idle.
Lastly it maybe the movement sensor that I believe is under the dash, there is a modification that can be done others will surely have more detail on this as it is something I have never come across before (thankfully).
However mine does take a second or so to settle down to a 900rpm idle.
If the search is working, you will find loads on this. The most likely culpret for the idle holding high after you come to a stop is not the stepper itself (although a good clean wont harm) is the speedo calibration unit fitted to cars with the ford gearbox. This small box of electronics sits under the dash, and produces a "car moving" signal at anything over 3mph. This makes the ECU lift the idle so you are less likely to get wheel lockup between gear changes. The problem is it has a tendency to produce a speed signal the car is still, so the ECU gets confused and holds the idle high. The electronics is very vunerable to stray voltages on the TVR earths causing it to trigger eratically. I have one in bits at the minute to see if I can make a plug in unit to reduce its sensitivity, but otherwise just check all your earthing points are clean for starters. You can tell for sure if this is the issue with the ECUmate or RoverGauge, as both have a speed display that shows if the signal is present, and if the ECU is in an idle status or otherwise.
Cheers Mark.
Just received my Ecumate reader. Interesting section on idle speeds here . . .
http://ecumate.com/docs/Ecumate%20inst.pdf
Just received my Ecumate reader. Interesting section on idle speeds here . . .
http://ecumate.com/docs/Ecumate%20inst.pdf
Indeed the idle control system is more complex than one would think. If you can get the car to idle correctly, you can increase the idle with ECUmate by adding stepper pulses to open up the air feed- typically 30 steps will lift the idle by a couple of hundred RPM. The ECU should pick this up and pull the idle back down quite quickly. This will prove the stepper is not sticking. It wont work the other way however, the ecu either does not respond quickly enough or at all to stop the engine dying. Also check the stepper position at idle- Im not sure how ECUmate displays this- but Rovergauge displays it as a percentage- and this is between 30 -40 % on a car with a correct idle. I would assume that this is a percentage of 180 steps- so if ECU mate displays steps Id think it would be 60-80 steps, but Ive not tested this with ECUmate. This will show the base idle setting is near correct, as the stepper is neather too far open or closed for idle control to work. Also note the throttle pot voltage is correct whith the throttle shut, and the speed reading is zero with the car stationary.
As for the mod' on the speedo calibration box if the speed signal is present, its a case of removing the unit and opening it up. It then needs a couple of resistors adding to one of the legs of the chip that picks up the speed tranducers signal to hold the pin above 0 volts, so it wont switch so easily if there are a few hundred millivolts on the earth connection. This is just one fix, I personally think you could simply add a small voltage to the tranducer cable to have the same effect with a plug in unit, but I need to have a closer look at the circuitry now I have a spare unit to play with.
As for the mod' on the speedo calibration box if the speed signal is present, its a case of removing the unit and opening it up. It then needs a couple of resistors adding to one of the legs of the chip that picks up the speed tranducers signal to hold the pin above 0 volts, so it wont switch so easily if there are a few hundred millivolts on the earth connection. This is just one fix, I personally think you could simply add a small voltage to the tranducer cable to have the same effect with a plug in unit, but I need to have a closer look at the circuitry now I have a spare unit to play with.
Edited by blitzracing on Friday 24th May 12:44
Mark. Keep up the good work on this. Solved my engine die at traffic lights with 'old school' technique. 2mm of plastic under the plenum throttle stop. Lucky me. Webber and SU technique. Still idles at 900rpm. Sometimes if restarted when hot idle drops away to 300 so I give it a blip of throttle.
Edited by EGB on Saturday 25th May 09:42
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