Eratic idle and misfire
Discussion
I've just completed 3500 miles in my 94 Griff in 4 weeks and I've now got a few niggly problems with it.
The idle speed will sometimes (nearly all the time now) increase upto as much as 2000rpm and then sometimes drop back down slowly. This to me pointed towards the stepper motor so I took it off and thorougly cleaned it, also took off the stepper motor receptor (don't know the word but the thing the stepper screws into) attached to the plenum and cleaned that. But this hasn't cured my problem.
I also have an intermitant misfire, it's ok at part throttle but as soon as I apply more throttle quickly it will miss fire badly. If I go WOT it will misfire badly but then sort of (90%, sometimes totally) clear itself over 3000rpm.
But then sometimes it will run absolutely perfectly, no problems at all. It isn't temperature related, it can play up at motor way cruise speed on a cold night or on a hot day in town.
Are the two problems related? Can a faulty stepper motor cause the misfire symtoms I've mentioned?
My guess is that the stepper motor has packed up.
The misfire may be due to me running out of fuel the other day (idiot) and sucking the bottom of the tank into the filter. But why is the problem intermitant?
Any help would be very much appreciated, it's sunny out and i'm on holiday and I can't drive my lovely griff
>>> Edited by DAVEHAMMERTON on Saturday 7th August 16:40
The idle speed will sometimes (nearly all the time now) increase upto as much as 2000rpm and then sometimes drop back down slowly. This to me pointed towards the stepper motor so I took it off and thorougly cleaned it, also took off the stepper motor receptor (don't know the word but the thing the stepper screws into) attached to the plenum and cleaned that. But this hasn't cured my problem.
I also have an intermitant misfire, it's ok at part throttle but as soon as I apply more throttle quickly it will miss fire badly. If I go WOT it will misfire badly but then sort of (90%, sometimes totally) clear itself over 3000rpm.
But then sometimes it will run absolutely perfectly, no problems at all. It isn't temperature related, it can play up at motor way cruise speed on a cold night or on a hot day in town.
Are the two problems related? Can a faulty stepper motor cause the misfire symtoms I've mentioned?
My guess is that the stepper motor has packed up.
The misfire may be due to me running out of fuel the other day (idiot) and sucking the bottom of the tank into the filter. But why is the problem intermitant?
Any help would be very much appreciated, it's sunny out and i'm on holiday and I can't drive my lovely griff
>>> Edited by DAVEHAMMERTON on Saturday 7th August 16:40
Suggestions:
Apart from getting dirty and needing the occasional clean the stepper motor is not a common item to pack up.
Is your coolant level topped up? Has the level dropped - you may get an air bubble in the system.
What sort of state are your HT leads? They have a hard life and once they start packing up that's that.
If your fuel level went down low you might have picked up some dirt. Best cure for that is probablygo and drive it another few thousand miles!
It's tough but someone's got to do it!!!
Apart from getting dirty and needing the occasional clean the stepper motor is not a common item to pack up.
Is your coolant level topped up? Has the level dropped - you may get an air bubble in the system.
What sort of state are your HT leads? They have a hard life and once they start packing up that's that.
If your fuel level went down low you might have picked up some dirt. Best cure for that is probablygo and drive it another few thousand miles!
It's tough but someone's got to do it!!!Thanks for the fast reply beano 
My coolant level is fine, doesn't use a drop.
My HT leads have had a hard life and I will be replacing them soon. But it's a complete misfire on all cylinders that's occuring, so it may be the king lead I suppose.
But that wouldn't make the idle eratic as well. Is there a way of testing the stepper motor? What should it do when I turn the ignition on and off?
My coolant level is fine, doesn't use a drop.
My HT leads have had a hard life and I will be replacing them soon. But it's a complete misfire on all cylinders that's occuring, so it may be the king lead I suppose.
But that wouldn't make the idle eratic as well. Is there a way of testing the stepper motor? What should it do when I turn the ignition on and off?
since I came to Germany my car does exactly the same. Yet when I am in the UK it doesnt do it at all!!!
I put it down to the increase in ambient temperature from ca. 18-24 now well over 30, at nighttime the car doesnt do it either in Germany when it cools to below 25...
>> Edited by sw2373 on Monday 9th August 07:51
sw2373 said:Could just be crap fuel in Germany!
since I came to Germany my car does exactly the same. Yet when I am in the UK it doesnt do it at all!!!
I put it down to the increase in ambient temperature from ca. 18-24 now well over 30, at nighttime the car doesnt do it either in Germany when it cools to below 25...
>> Edited by sw2373 on Monday 9th August 07:51
The problem did develop whilst out in Germany but I don't think it's to do with the fuel because it's better out there than it is in the UK as has been said.
The car is in England now and the problem still exists. Is there a way to check the stepper motor? I'm sure it's not working as intended.
Also can I get a fuel filter for it from Halfords? If so what's the part number or common car.
Thanks again.
The car is in England now and the problem still exists. Is there a way to check the stepper motor? I'm sure it's not working as intended.
Also can I get a fuel filter for it from Halfords? If so what's the part number or common car.
Thanks again.
Just thought i'd let you know what the problem was.
The ECU had been cable tied to the heater hoses (I suppose in an attempt to remedy TVR poor idea of slinging it ontop of the battery!).
This was causing the ECU to get very hot, the trouble was it was very difficult to spot a pattern to when the problem would occur and when it wouldn't.
I went to disconect to ecu and re-attach it to see if it'd cure the problem by resetting it, and the thing was very very hot to the touch. This was a moment enlightenment (spelling), and felt very sweet when it dawned on me that this was causing my problems
This was two weeks ago and I haven't had a single problem with it since. The ecu now sits away from the heater hoses.
Anyway I just thought i'd give you some feedback and say thanks again to everyone who helped.
I hope this may help someone in the future because it really is crap when your Griff isn't running right.
Dave
The ECU had been cable tied to the heater hoses (I suppose in an attempt to remedy TVR poor idea of slinging it ontop of the battery!).
This was causing the ECU to get very hot, the trouble was it was very difficult to spot a pattern to when the problem would occur and when it wouldn't.
I went to disconect to ecu and re-attach it to see if it'd cure the problem by resetting it, and the thing was very very hot to the touch. This was a moment enlightenment (spelling), and felt very sweet when it dawned on me that this was causing my problems
This was two weeks ago and I haven't had a single problem with it since. The ecu now sits away from the heater hoses.
Anyway I just thought i'd give you some feedback and say thanks again to everyone who helped.
I hope this may help someone in the future because it really is crap when your Griff isn't running right.
Dave
Sorry to ressurect an old thread, but just come across this when searching about idling problems. The ECU should of course not be tied to the heater hoses (obviously), but nor should it be slung on top of the battery! It should be a snug fit down the side of the battery box where there is no risk of it shorting across battery terminals!
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