High idle when coasting / throttle over-run
Discussion
I've been struggling a bit with idle speed recently. When stationary the idle is set up fine. However out on the road its a different story. When coasting or on throttle over-run the engine is still pulling about 1800-2000 rpm. As I come to a stop it will settle at around 900rpm again. So with no throttle input applied and at relatively low speeds (circa 25 mph) when in 2nd gear (or even 3rd) I'm holding speed, not slowing down.
I've tried the SC-Power stepper motor restrictor, which was generally OK, but occasionally the engine revs would fall right off and the engine would cut out (especially when dipping the clutch and changing down gear in a non-rushed way). I've tried various adjustment on the hex-screw on top of the plenum inlet - but I'm not getting very far.
Any ideas much welcomed, thanks
I've tried the SC-Power stepper motor restrictor, which was generally OK, but occasionally the engine revs would fall right off and the engine would cut out (especially when dipping the clutch and changing down gear in a non-rushed way). I've tried various adjustment on the hex-screw on top of the plenum inlet - but I'm not getting very far.
Any ideas much welcomed, thanks
Sticky idle stepper motor.
System is designed so that when coasting, with throttle closed, the transducer on the diff (the same one that signals the speedo) controls the ecu to hold a higher setting on the stepper. Only when you come to a standstill will the transducer acknowledge this and allow the stepper to reduce idle to 900rpm.
Coasting idle will be around 1200rpm but if the stepper is lazy or base settings wrong then it will stick at about 2000. My car had this problem and only solved by regular use. If left standing for a while it will take a few miles to sort itself out again.
A good clean or regular use should cure things.
System is designed so that when coasting, with throttle closed, the transducer on the diff (the same one that signals the speedo) controls the ecu to hold a higher setting on the stepper. Only when you come to a standstill will the transducer acknowledge this and allow the stepper to reduce idle to 900rpm.
Coasting idle will be around 1200rpm but if the stepper is lazy or base settings wrong then it will stick at about 2000. My car had this problem and only solved by regular use. If left standing for a while it will take a few miles to sort itself out again.
A good clean or regular use should cure things.
Had this problem with my Chimaera 450 every time the stepper motor has been didconnected from the battery. This is how I was told to fix it.
Disconnect stepper, turn ignition on for 10 seconds
Connect stepper ignition on for 10 seconds
ignition off for 10 seconds
ignition on for 10 seconds then start engine
Problem sorted, no cost no tools and no effort.
Have posted this up before and various people have said its rubblish, but it has worked every time for me.
mentioned this recently to Dan Taylor (TVR specialist near Maidstone),
he said that its usually not needed on 400's or 500's but that the 450 is a bit more suscentable to this problem also that they tend to overfuel.
Disconnect stepper, turn ignition on for 10 seconds
Connect stepper ignition on for 10 seconds
ignition off for 10 seconds
ignition on for 10 seconds then start engine
Problem sorted, no cost no tools and no effort.
Have posted this up before and various people have said its rubblish, but it has worked every time for me.
mentioned this recently to Dan Taylor (TVR specialist near Maidstone),
he said that its usually not needed on 400's or 500's but that the 450 is a bit more suscentable to this problem also that they tend to overfuel.
Im sure I have read in "the bible" somewhere that the sensor for the speedo (Not sure where it is located) also tells the ECU if the car is moving or stationary. Not quite sure for what purpose, but a friend of mine had trouble with erratic tickover (I know not your symptoms), changed this sensor and all was well again. How well does your speedo work and low speeds?
JiltedJohn said:
I thought they were slow to come back down the last few RPM by design to prevent rear wheel lockups.
I thought that too,and mine never acted like this until i had the plenum off/cleaned the stepper motor..... now it does it,but not to the extreme some people are seeing,holds at roughly 1200 rpm till the car comes to a stop,then dros to standard idle speed,this i think is how it should be.Thanks all for the support. I've been away all week but will be in the Griff at the weekend, so will report back then on the suggestions made. Stepper motor etc all very clean so doubt its linked to that.
Interested about the post linking it to speedo transducer. I did have some problems at the beginning of the year with this. I had a gearbox change, but the garage had the wrong type of worm gear (?) fitted inside the gearbox that provides input to the transducer. This gave a speedo reading that was significantly wrong (by about 20 mph at 70 mph). The gearbox was dropped again and the right 'internals' fitted. That brought the speedo accuracy back. It's now bang on give or take a couple of mph or so.
cheers
Interested about the post linking it to speedo transducer. I did have some problems at the beginning of the year with this. I had a gearbox change, but the garage had the wrong type of worm gear (?) fitted inside the gearbox that provides input to the transducer. This gave a speedo reading that was significantly wrong (by about 20 mph at 70 mph). The gearbox was dropped again and the right 'internals' fitted. That brought the speedo accuracy back. It's now bang on give or take a couple of mph or so.
cheers
Thanks all for the support. I've been away all week but will be in the Griff at the weekend, so will report back then on the suggestions made. Stepper motor etc all very clean so doubt its linked to that.
Interested about the post linking it to speedo transducer. I did have some problems at the beginning of the year with this. I had a gearbox change, but the garage had the wrong type of worm gear (?) fitted inside the gearbox that provides input to the transducer. This gave a speedo reading that was significantly wrong (by about 20 mph at 70 mph). The gearbox was dropped again and the right 'internals' fitted. That brought the speedo accuracy back. It's now bang on give or take a couple of mph or so.
cheers
Interested about the post linking it to speedo transducer. I did have some problems at the beginning of the year with this. I had a gearbox change, but the garage had the wrong type of worm gear (?) fitted inside the gearbox that provides input to the transducer. This gave a speedo reading that was significantly wrong (by about 20 mph at 70 mph). The gearbox was dropped again and the right 'internals' fitted. That brought the speedo accuracy back. It's now bang on give or take a couple of mph or so.
cheers
.... just to update you on this. I tried TVR Keith's routine above. Although early days (it was a short test drive) and to my surprise it does appear to have improved the situation. Thanks TVR Keith! I can't understand why or how this would have improved the idle when at a reasonable road speed....but it has, at least for the time being.
JKY said:
Sticky idle stepper motor.
System is designed so that when coasting, with throttle closed, the transducer on the diff (the same one that signals the speedo) controls the ecu to hold a higher setting on the stepper. Only when you come to a standstill will the transducer acknowledge this and allow the stepper to reduce idle to 900rpm.
Coasting idle will be around 1200rpm but if the stepper is lazy or base settings wrong then it will stick at about 2000. My car had this problem and only solved by regular use. If left standing for a while it will take a few miles to sort itself out again.
A good clean or regular use should cure things.
System is designed so that when coasting, with throttle closed, the transducer on the diff (the same one that signals the speedo) controls the ecu to hold a higher setting on the stepper. Only when you come to a standstill will the transducer acknowledge this and allow the stepper to reduce idle to 900rpm.
Coasting idle will be around 1200rpm but if the stepper is lazy or base settings wrong then it will stick at about 2000. My car had this problem and only solved by regular use. If left standing for a while it will take a few miles to sort itself out again.
A good clean or regular use should cure things.
Troogly said:
.... just to update you on this. I tried TVR Keith's routine above. Although early days (it was a short test drive) and to my surprise it does appear to have improved the situation. Thanks TVR Keith! I can't understand why or how this would have improved the idle when at a reasonable road speed....but it has, at least for the time being.
Glad it worked for you, perhaps some of the people who have said this is rubbish will start to believe that its worth a tryGassing Station | Griffith | Top of Page | What's New | My Stuff