Discussion
I've got the common problem of poor idling on my 4.0l pre cat. I've tried the ususal tweaks of cleaning the stepper motor, checking for air leaks and resetting the ECU. I'm at the point where I start thinking about replacing bits. First on my list is a new stepper motor which can be cheap (from £14 on eBay) or expensive (£93 at TVRParts). Has anyone had any experience with the eBay steppers?
Starts from cold OK with foot on the gas, but won't maintain an idle when you lift your foot off. The problem continues until the engine gets fully warmed up. Here's the strange thing, once the engine is warm and the car is idling nicely at about 1000rpm I can switch the engine off, then restart almost immediately and the car won't idle again!
On the origional question of ebay steppers..They are replicas made in China, and the one I got was rubbish. The motor was badly fitted into the housing, letting air past the motor, so it never worked as it should. I know of some people have bought them and they seem OK, but you get what you pay for but you might be lucky. I have heard that you can pay around £60 for the OEM unit if you shop around. You could also try winding up the base idle screw a bit, it will alter the range the stepper moves over if there is one sticky point in its travel. If you want to see if the stepper is moving OK, then disconnect it when the car is running, then stop the engine and let it cool. Then remove the stepper, and reconnect it, and turn the ignition on and off whilst looking at the motor. It should pull the cone right back smoothly as the ignition goes OFF. (This is part of the restart sequence to provide more air for restarting) It will only move once.
Mark
Mark
OK, I went through the process of warming the engine, getting a stable idle and removing the wiring connector to the Stepper. The engine continued to idle smoothly but when I switched it off and back on it was the same problem. The engine wouldn't idle immediately, it just stalled, but with a bit of coaxing on the throttle, for say 10 or 15 seconds, the idle stabilised at around 1000rpm.
This suggest to me that the stepper is behaving itself and there's another sensor feeding back the wrong info or the ECU is misbehaving?
Mark, thanks for your input These problems can become messy enough without further complicating the picture with a dodgy new part. I'll certainly avoid the eBay steppers if I still need to take that route.
This suggest to me that the stepper is behaving itself and there's another sensor feeding back the wrong info or the ECU is misbehaving?
Mark, thanks for your input These problems can become messy enough without further complicating the picture with a dodgy new part. I'll certainly avoid the eBay steppers if I still need to take that route.
If you need a cheap stepper, i've just taken mine off, having replaced it with a two-wire type to work with the new Emerald system. It was in perfect working order before I took it off and will come up as good as new with a little white spirit to remove the the carbon buildup. Not really sure what it's worth, but a few beer tokens would be nice given that the Emerald setup has rendered me poor!
Edit: just read the last post saying it's probably not the stepper so never mind! Offer still stands though if you start replacing bits..!
Edit: just read the last post saying it's probably not the stepper so never mind! Offer still stands though if you start replacing bits..!
Edited by thenick on Thursday 24th January 18:01
Griff4.0 said:
. The engine wouldn't idle immediately, it just stalled, but with a bit of coaxing on the throttle, for say 10 or 15 seconds, the idle stabilised at around 1000rpm.
This suggest to me that the stepper is behaving itself and there's another sensor feeding back the wrong info or the ECU is misbehaving?
Just the opposite, The stepper should wind back in when you turn the ignition off. This opens up the airflow to maximum, ready to restart. (You may have noticed "a blip of throttle" on restart when all was working). On starting, it should then wind back out to reduce the airflow in the first few second seconds to stablise the tickover. My ecu does this process what ever temperature the engine is. (1992 ECU- just incase theres be a programming change subsiquently!). Its possible you have lost stepper feed, but again if you take it out, and then cycle the ignition on /off, you should at least feel it vibrate even if it wont move if it has supply. The ECU's themselves are pretty tough.This suggest to me that the stepper is behaving itself and there's another sensor feeding back the wrong info or the ECU is misbehaving?
blitzracing said:
Just the opposite, The stepper should wind back in when you turn the ignition off. This opens up the airflow to maximum, ready to restart. (You may have noticed "a blip of throttle" on restart when all was working). On starting, it should then wind back out to reduce the airflow in the first few second seconds to stablise the tickover.
The point is that the right position after the restart is the same as the right position before the restart. With the stepper already in the right place, the engine should have stabilised almost immediately and settled back at the same idle. The fact that it didn't suggests that something else is going wonky after the restart.GreenV8S said:
blitzracing said:
Just the opposite, The stepper should wind back in when you turn the ignition off. This opens up the airflow to maximum, ready to restart. (You may have noticed "a blip of throttle" on restart when all was working). On starting, it should then wind back out to reduce the airflow in the first few second seconds to stablise the tickover.
The point is that the right position after the restart is the same as the right position before the restart. With the stepper already in the right place, the engine should have stabilised almost immediately and settled back at the same idle. The fact that it didn't suggests that something else is going wonky after the restart.blitzracing said:
Mine goes through the stepper motor reset every ignition off cycle, so it always has to drop the RPM once the engine has started. (Can make you feel a bit of a pratt like you are blipping the throttle to draw attention !). It is possible the ECU programming has changed over the years to alter this start cyle however? The symptoms perfectly match a completely stuck stepper, providing enough air for a warm engine in its stuck position to tickover, but not enough on a cold restart.
Are you talking about a cold restart, or hot? The car is needing throttle for fifteen seconds or so to keep running after a hot start. If the stepper was already in the right position when the engine started it should have settled back to the normal idle speed within moments. If the ECU / stepper are connected and working correctly, the stepper should already have been open leading to a high idle which should settle within a second or two as the stepper moves back to the original idle position. If it's staying low for that long either the stepper is closed and taking a long time to open, or something else is wrong. Disconnecting the stepper should tell us whether it's the stepper causing this, or something else.Edited by GreenV8S on Friday 25th January 13:38
Griff4.0 said:
Starts from cold OK with foot on the gas, but won't maintain an idle when you lift your foot off. The problem continues until the engine gets fully warmed up. Here's the strange thing, once the engine is warm and the car is idling nicely at about 1000rpm I can switch the engine off, then restart almost immediately and the car won't idle again!
This is the bit Ive made the assumptions on, not a hot engine. Otherwise I totally agree with you. To me this shows the stepper not opening when cold, and not opening for restart, but a combination of base idle settings and possible small stepper opening (as in stuck) being enough to keep the engine idling once warm. After all the base idle is set to 800 or so rpm with the engine warm, and no stepper airflow whatsoever. Gassing Station | Griffith | Top of Page | What's New | My Stuff