Rough idle on startup.
Discussion
Got it up to working temp but stil need to keep my foot on the accelerator pedal otherwise it just dies. Going to borroow a fault code reader and see if that can shed any light. But would an air leak in the plenum cause this sort of problem. Or what else could it be the means that it just will not idle.
During my discussion with Jason at Str8Six while I was stranded in Paris, he mentioned that even if only one cylinder isn't firing then the engine will not idle. Starting from cold, try getting an assistant to keep it running while you touch the end of a cable tie against each branch of the exhaust manifolds. When you find a cylinder that doesn't melt the plastic, there's your problem!
Quietlybonkers said:
Silly thought - mine went rough without warning, and chucked out smoke on startup, and it was solved by a friend/mechanic pushing the number 8 plug lead back on
Yes, I had this last week. Rough idle until warm then ok. Bought a new set of leads and when removing lead from No 8, realised the extender wasn't seated properly. All now seems ok (and I've a spare set of leads!). Definitely worth checking. Cheers.
One more random thought, also probably wrong.
Dying when idling, unless you keep your foot in, is what happened on mine when the 100 amp fuse blew. It kept feeling like it was going to stall at every junction.
Not much later the car died completely, as it had been running on battery (100 amp is between alternator and battery), and so when the battery was dead so was the car.
Might just be a coincidence, but if something you did could have blown this fuse it might just explain in. You would notice very little wrong until the battery was well drained, and then random things like the speedo misreading, the alarm going bonkers start happening. The fuse is strapped under the driver's side chassis, about where the front lower wishbone joins the chassis - rear attachment.
Dying when idling, unless you keep your foot in, is what happened on mine when the 100 amp fuse blew. It kept feeling like it was going to stall at every junction.
Not much later the car died completely, as it had been running on battery (100 amp is between alternator and battery), and so when the battery was dead so was the car.
Might just be a coincidence, but if something you did could have blown this fuse it might just explain in. You would notice very little wrong until the battery was well drained, and then random things like the speedo misreading, the alarm going bonkers start happening. The fuse is strapped under the driver's side chassis, about where the front lower wishbone joins the chassis - rear attachment.
Thanks for the ideas, i'll check the fuse, I have installed a volt meter in the dash and it was showing about 14 volts so this is possibly not the problem. I have had the car completly apart to referb the chassis and so this is the first time since then that it has run so it could be a number of things. Any way here is a pic of the engine bay and you can see I have moved the 100amp fuse to the bracket that holds the alternator. Should make it easier to keep an eye on it and no road muck etc to get at it either.
I'll check again all the plug leads and the extenders to check that they are all seated.
I'll check again all the plug leads and the extenders to check that they are all seated.
Edited by Pink_Floyd on Sunday 12th August 20:52
blitzracing said:
Ah ha- see the fault the AFM is missing and the HT leads not attached! If its been to bits did you remove the unused manifold preheat plate under the throttle body? It lets in air and it wont idle if you do.
Well spotted. AFM is now in and HT leads attached. I did remove the preheat plate but blocked off the bolt holes with shorter bolts, does it let air in any other way other than the bolts without that plate on ?just the bolts- the symptoms of a largish air leak are it will start and run for about 3-5 seconds and then die as it ignores the AFM output just to get the engine started, and the injector pulse widths are fixed to start with. Then once the engine fires the AFM reading is taken and the fueling set by the ECU. If you have a leak, the airflow value will be too low, so the engine leans out and dies after the initial period (or runs badly).
OK thanks for the info. The car won't idle at all unless I keep my foot slightly on the accelerator. So which of the following is most likely.
1 by keeping my foot on the accelerator, if I have an air leak then the throtle pot will be saying to the injectors (via ecu) add fuel.
2 If it has enough fuel then by having my foot on the accelerator then this is adding air in, indicating that the air bypass is blocked or something.
Is it possible that by removing the manifold preheater that the bolts that I put back in have affected the air bypass and I need to adjust it.
as per the following
Base idle adjustment is made by turning a set screw that's normally hidden under a tamper-resistant plug on the Throttle body. To access the screw, first drill a small hole (typically 1/8") in the tamper-resistant plug. Thread a sheet metal screw into the hole, and then pry the screw & plug out together. The main throttle butterfly is fully closed at idle, so there is a air bypass screw adjustment on the top of the plenum chamber that works together with the stepper motor. The screw adjustment is factory set, and sealed with a cap, and normally will not need adjusting. To set this setting start the car (it needs to be warm) and adjust the screw for a tick over of about 600 rpm. Once set the rubber bung can be removed from the feed pipe, and the stepper motor should lift the tick over to around 800 rpm (This speed is set by a setting in the fuel map, and is not manually changeable). If you are running without a stepper motor a base idle of around 900 rpm will suffice.
1 by keeping my foot on the accelerator, if I have an air leak then the throtle pot will be saying to the injectors (via ecu) add fuel.
2 If it has enough fuel then by having my foot on the accelerator then this is adding air in, indicating that the air bypass is blocked or something.
Is it possible that by removing the manifold preheater that the bolts that I put back in have affected the air bypass and I need to adjust it.
as per the following
Base idle adjustment is made by turning a set screw that's normally hidden under a tamper-resistant plug on the Throttle body. To access the screw, first drill a small hole (typically 1/8") in the tamper-resistant plug. Thread a sheet metal screw into the hole, and then pry the screw & plug out together. The main throttle butterfly is fully closed at idle, so there is a air bypass screw adjustment on the top of the plenum chamber that works together with the stepper motor. The screw adjustment is factory set, and sealed with a cap, and normally will not need adjusting. To set this setting start the car (it needs to be warm) and adjust the screw for a tick over of about 600 rpm. Once set the rubber bung can be removed from the feed pipe, and the stepper motor should lift the tick over to around 800 rpm (This speed is set by a setting in the fuel map, and is not manually changeable). If you are running without a stepper motor a base idle of around 900 rpm will suffice.
An air leak has the biggest effect when the throttle plate is shut, so you have a large vacuum in the plenum, plus little air going through the AFM, so any air leak really weakens the mixture. When you open the throttle the vacuum drops, so less air is drawn in through the leak, plus the afm flow is greater so the engine gets more fuel. You can certainly try raising the base idle by winding the screw up, (It wont do any harm) and see if you can get a stable idle.
A mate came over today and we got the car ideling, as it was sort of ideling rough we removed 1 plug at a time and got to a point where it was just running on 6 cylinders. So changed the 2 plugs on the other cylinders and it was ideling as sweet as can be. Plugged in Blitzracing lead with rovergauge and this showed everything was fine, fans cut in and then out and it was ideling well. so turned it off had dinner etc, Went out this evening, engine nice and cold and it won't idle, didn't bother gettting it hot to see if it would idle properly. So not sure what to do next, but i suppose that it could be an air leak which seals up as everthing gets warmed up and expands.
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