hi - I've been having idle hunting/ stalling issue with my classic 4.2 lse. Problem started as it came out of a garage after having some (non engine) work carried out. The only thing the guy did was to wind the idle down a little as it surged when putting it into park. Since then the idle has been erratic so I've changed the steeper motor, cleaned the maf, pipes and flame trap. Prior to this ( a few months ago) it's had a new dizzy/ cap/arm/plugs and leads. I tried to set the base idle today as per instructions on the net but when I take the stepper lead off and start in neutral it stays at 1500-2000 regardless of adjustment? Does anyone have any ideas or thoughts on what i should be checking next? Doesn't seem to have leaks from the pipes as I've checked by spraying around them with no raise/fall noticed. Now it doesn't seem to want to idle at all and just hunts then dies?
Many thanks
Matt
The engine will idle fast if you remove the stepper plug. (IIRC the ecu winds the stepper to full open when you switch off, that could be on but you get the picture) It will also cause an ecu fault and put it in limp mode.
I would suggest you need to go at this one bit at a time.
First up, disconnect the main ecu plug under the drivers seat, wait a couple of seconds then put it back on, next turn ignition on and listen, you should hear the fuel pump, efi and brake system relays click. Check dash, hopefully the efi warning light is out.
Do a quick check to make sure all the hoses are connected and that there are no air leaks, so look at bypass air hose (the big one round the back that goes to the stepper), check the vac line that goes from the base of the ram housing to the vacuum accumulator and also check the vacuum connection on the crank case breather system ( the connection to the pipe off the top of the flame trap), last have a look at the hose for the fuel pressure regulator. You shouldn't need to worry about the vac advance hose at this stage as it doesn't do anything at idle ( but do check the vac advance for correct operation). Assuming all is in order fire up the engine and let it warm up, it needs to be warm or the idle will be high due to cold start enrichment.
Assuming the engine has been able to warm up you need to check the ignition timing. It needs to be at 8 Degrees BTDC +/- 1 degree.
Assuming (again) timing is good and the engine will idle smoothly you need to then go about setting the base idle. I find the easiest way to do this is to pull the bypass air hose off at the stepper motor then block off the end of the metal pipe either by putting duct tape over it or get a small plastic bag, cover the end of the pipe then put the bypass air pipe back on over the top. Now the stepper can't do anything to change the idle speed.
You might find the engine will not idle at all meaning the base idle is too low. BTW you'll need to give it a little bit of throttle to start up and then
VERY SLOWLY ease the throttle back or it will almost certainly stall, if it stalls anyway the base idle is too low. Find a suitable allen key and turn the idle speed adjuster counter clockwise. You might need a couple of goes to get the engine to idle then you can adjust it until you get the desired 500rpm. If everything is in order, with care it is possible for the engine to sort of idle as low as 250 - 300rpm (I did this very thing just last week on my 3.9).
If you still can't get a smooth idle then I would suspect an inlet air leak somewhere. Get yourself a vacuum gauge to test. Another way to check is to remove the air filter from in front of the air flow meter then with the engine running slowly move your hand across the front of the AFM, as the opening is progressively covered, the idle should improve if there is an inlet air leak before the air flow is too restricted at which point it should suck your hand tight up to the AFM and stop.If the vacuum doesn't feel very strong or you can completely cover the air flow meter and the engine still runs you have an inlet air leak.
Sorry for the long post but hope that helps. Let us know how you get on.
