Hunting/surging at idle when cold
Discussion
Hello chaps!
Trust you all have your heaters on? Sunny and 22degs today just in case you were wondering.
I've recently been going over the engine on my 400SE concentrating on electrics and checking sensor readings etc. etc. All is good and after a good clean and the odd adjustment it's definitely running better.
I've also adjusted the timing to around 8-9deg BTDC (interestingly still no pinking on unleaded) and bug*ered around with the mixture screw on the AFM as it has always seemed to run lean. HOWEVER, it is now hunting at idle when cold, it does it for around a minute or two then it's fine.
I do recall hearing in the distant past that hunting was reasonably common on the SD1 and Rover added a resistor across the coolant temp sensor which cured it. However I'm assuming it must have something to do with the mixture as I've played around with it. I have some data that states that the normal output (i.e.correct adjustment) from the AFM should be between 0.9 and 1.4v, I have 1.1v. I'm getting way more snap, crackle and pop too
but I assume that's suggesting unburnt fuel and hence the mixture is too rich????
Anyone got any ideas? And whilst I'm at it without a CO meter is there any way to adjust the mixture correctly other than trial and error and checking the plugs etc.?
Timbo
Trust you all have your heaters on? Sunny and 22degs today just in case you were wondering.
I've recently been going over the engine on my 400SE concentrating on electrics and checking sensor readings etc. etc. All is good and after a good clean and the odd adjustment it's definitely running better.
I've also adjusted the timing to around 8-9deg BTDC (interestingly still no pinking on unleaded) and bug*ered around with the mixture screw on the AFM as it has always seemed to run lean. HOWEVER, it is now hunting at idle when cold, it does it for around a minute or two then it's fine.
I do recall hearing in the distant past that hunting was reasonably common on the SD1 and Rover added a resistor across the coolant temp sensor which cured it. However I'm assuming it must have something to do with the mixture as I've played around with it. I have some data that states that the normal output (i.e.correct adjustment) from the AFM should be between 0.9 and 1.4v, I have 1.1v. I'm getting way more snap, crackle and pop too
but I assume that's suggesting unburnt fuel and hence the mixture is too rich????Anyone got any ideas? And whilst I'm at it without a CO meter is there any way to adjust the mixture correctly other than trial and error and checking the plugs etc.?
Timbo
I have the same problem with my 350i
Took it for an MOT begining of the year and it was running lean, so while I was there they corrected it for me.
Since then when starting, only from cold it would surge and hunt for the first 30-60 seconds then run perfectly well.
I disconnected the cold start injector and it fine now but I would prefer it to be sorted correctly. so if you figure out the problem please let me know.
Took it for an MOT begining of the year and it was running lean, so while I was there they corrected it for me.
Since then when starting, only from cold it would surge and hunt for the first 30-60 seconds then run perfectly well.
I disconnected the cold start injector and it fine now but I would prefer it to be sorted correctly. so if you figure out the problem please let me know.
I'm on hotwire but as I mentioned I'm pretty sure the SD1 had the same problem and Rover retro fitted a resistor across the coolant temp sensor which fooled the ECU into thinking the temp was higher than it actually was and then I guess made the mixture less rich. I may try that but at this stage I'm thinking my mixture is all wrong!
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