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Idle speed changes 1-2K every 10 seconds, Bizzare
HI all,
I have been running my newly built RS Turbo in now for around 350 miles, nearly due for an oil change. all is going very well, however, the idle is very strange, it hunts around but in a stable condition, it will start and rev straight to 2000rpm, then drop to 1000rpm after a few seconds, then if left, it will simply sit and every 10 seconds switch from running at 1000rpm to 2000rpm, Its so bizarre, i have set the AFR to approx 14.7 when warm and idling at 1000rpm. Cleaned and even swapped the idle valve with no change, the TPS was cleaned and then changed out for another one, the coolant temp seems fine, Fuel pressure is 38psi when idling and vac attached, Whilst driving, once i dip the clutch the revs will rise from whatever they were, to about 2200 for 5 seconds or so, and then settle, sometimes it doesn't settle out. Pulling up to a junction, the revs sit high for some time before eventually dropping, seems just touching the throttle makes the revs rise and then hold high Its on standard OFAB and blue injectors, turbo boost is connected straight to the waste gate whilst running in, so the amal/ electric bleed valve is unplugged. Disconnecting the VSS makes no difference. The only thing that isnt standard as such, is the turbo is a T3 turbo and not a T2, but ive not heard of this behaviour before, once its run in and covered a few more easy miles, i will get a MSD chip for the T3 and have it set up. Anyhow, for now, im just looking for a reason why this might happen Thanks in advance |
It does sound like something is compensating for something like a Vacuum leak, idel controle or TPS issue...unless the target AFR is not possible?. I wonder if a trip to MSD might be the best way to get the car sorted and chipped?
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That's what i have been thinking, its very strange, i would have thought a vacuum leak into the manifold would cause a more constant like revving, its almost like its in a test mode or something,
i was suffering with poor low down throttle control and similar idling, although it would jump from base idle to 2000rpm and kicking quite violently when coming on throttle, so i re-checked the AFR and it was very lean, After resetting the AFR and fuel pressure it now drives very nicely both low down and through the throttle onto boost, but the constant revving up and down is worrying me, as it will idle very fast when first started. When it hits 1000rpm, it sounds lovely and with a lambda value of 0.98 which is about 14.7 ish. I wasn't sure if the ECU needs to re-learn or something after changing the Co pot settings and fuel pressure I will be taking it to MSD, but that distance a the moment i think is a bit risky, especially if i get caught in traffic with it revving its bits off. |
Originally Posted by 90_spec
(Post 6785918)
That's what i have been thinking, its very strange, i would have thought a vacuum leak into the manifold would cause a more constant like revving, its almost like its in a test mode or something,
i was suffering with poor low down throttle control and similar idling, although it would jump from base idle to 2000rpm and kicking quite violently when coming on throttle, so i re-checked the AFR and it was very lean, After resetting the AFR and fuel pressure it now drives very nicely both low down and through the throttle onto boost, but the constant revving up and down is worrying me, as it will idle very fast when first started. When it hits 1000rpm, it sounds lovely and with a lambda value of 0.98 which is about 14.7 ish. I wasn't sure if the ECU needs to re-learn or something after changing the Co pot settings and fuel pressure I will be taking it to MSD, but that distance a the moment i think is a bit risky, especially if i get caught in traffic with it revving its bits off. I would consider the expense of a trailer journey and know it will be 100% sorted. |
Ill look into the costs then, i just really like to try and solve silly issues like this myself, but i must admit, this one has me stumped, apparently there is a procedure for setting the idle values for EEC-IV that i found, so ill give that a try too.
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Ive been doing some more looking into this,
If i leave the Idle valve completely disconnected, the car and starts, a little lumpy when really cold, but within 2 minutes its ticking over at 1000rpm with no issues at all. With the ISCV plugged in the car will increase and decrease its RPM which is caused by the ISCV,, looking at the signal voltage with respect to GND, it sits at 5V when idling at 1300 and then for no reason it will run to 3V ,(increasing duty) this cycle repeats every 10-15 seconds continually. The base idle screw is in the right place when comparing to other throttle bodies ive seen, the TPS voltage with IGN on and engine off is 0.67V and i have checked there are no bad spots. Last night , i unplugged the ECU for 5 minutes and reconnected it and started the engine with the ISCV plugged in, it immediately revved and then settled to 1000rpm, sat for nearly 3 minutes, and then began to hunt up and down, arrrgh!! The CO pot signal voltage is 3.5V, but the AFR with the ISCV off is 15 ish or 1.01 lambda when warm so the fuelling should be right Its really bugging me now, i just cant figure out why the ECU is always cycling the demand for the ISCV. I know it needs setting up with the correct chip, but this sort of behaviour is just something very silly that i cant seem to pinpoint. Any OFAB RST experts out there??? Cheers Rich |
Just a thought but what engine breather you using and do you still have the connection to the inlet manifold? because if it’s open to atmosphere after the breath it could be that sucking in a load of air. |
Hi buddy, fun y you ask actually as I’ve just bought the cone shaped breather today which I think is the later one that I’ll fit now. But currently it has the standard canister shaped one with the ford logo, small pipe to the inlet tracts with the one way valve , arrow pointing towards the intake, the top connection to the rocker cover and the bottom one that would have been on the air box is currently in a vented plastic bottle to catch the oil vapour, I have a small amount of oil in there after 500 miles of running in, perhaps a teaspoon full. What are your thoughts on that? Appreciate the help 😁 Rich |
Ok, fitted the newer breather pot, no change, blanking the hose from the inlet tract to breather helped a lot with the idle speed with the ICSV connected, but the revs still hunt consistently with it connected. I set the CO pot to give me lambda 1 when the car was hot and iSCV connected, revs around 1200 , can’t see any leaks, used leak spray etc. I have noticed tho that if I rev the car, the AFR immediately goes lean, like 1.16 lambda, that’s worrying I thought, but maybe it’s the response time as I’m statically revving it and it’s not under load. I.e the engine can rev freely and the ÉCU can’t compensate that fast unless it’s driving conditions. Impretty much at a loss now. Rich |
Mine would never run right with the breather to inlet and open ended to catch tank as basically it’s a air leak. So plugged it permanently and just had normal engine breather setup. Get the co and base idle set to see if it improves. Other problem could be the ideal control valve is worn or passing, leaving it over night in petrol to clean up. |
idle problem
id suggest throttle positon sensor .id you google it or check manual it will give you resistance value of sensor at idle and full throttle . You can check it by plugging cable off sensor and measuring between two terminals on sensor with a meter . You set meter to ohms . I have manual somewhere I will check for you . All sensors on de car have an ohm value and can be checked to see if they’re within tolerances |
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