S1 Elise occasional misfire
Discussion
For 6 months now I've lived with an intermittent glitch with my 98 Elise. Standard K series but with 135 head. I fitted a Janspeed 4-2-1 manifold and sports cat last year with new oxygen sensor. Since my issue started soon after, it made me suspect this but troubleshooting seems to be pointing elsewhere, possibly to MAP sensor. O2 sensor is currently unplugged and problem still occurs. Throttle position sensor has also been replaced with a spare, but problem still occurs.
Symptoms as follows. Car starts fine, runs fine, sometimes doesn't fault at all. Problem usually occurs at least 45 mins into journey, driving style doesn't seem to provocate the issue. Car will suddenly start to run rough at steady throttle, with small inputs causing jerkiness. Full throttle and all is good (so when fuelling is in open loop, problem appears to be bypassed?). Once stopped, car idles ok but gently increasing throttle causes hunting of revs at low revs. As revs are gently increased over 2k ish it just accelerates roughly.
Every time this has occurred, when I turn ignition off and wait for a minute before restarting it has cleared the problem and the car has continued happily for the remaining journey, often another hour or so.
Earlier in the year the car was checked over. Fault codes hadn't been cleared for a while but the one unaccounted code suggested MAP sensor may be the issue.
To me, it seems too consistent to be a fuel issue or even spark plugs, leads playing up. Ignition off reset seems to point to electrical, and symptoms suggest the car is suddenly running lean or rich. I've read up on the other sensors but it doesn't sound like they would manifest in this way if misbehaving. The car lives inside and the atmosphere is pretty dry here in sunny Christchurch NZ. But local K series knowledge is a bit thin on the ground...
A few threads I've read are similar but not identical. Has anyone had this issue and confirmed the fix?
Symptoms as follows. Car starts fine, runs fine, sometimes doesn't fault at all. Problem usually occurs at least 45 mins into journey, driving style doesn't seem to provocate the issue. Car will suddenly start to run rough at steady throttle, with small inputs causing jerkiness. Full throttle and all is good (so when fuelling is in open loop, problem appears to be bypassed?). Once stopped, car idles ok but gently increasing throttle causes hunting of revs at low revs. As revs are gently increased over 2k ish it just accelerates roughly.
Every time this has occurred, when I turn ignition off and wait for a minute before restarting it has cleared the problem and the car has continued happily for the remaining journey, often another hour or so.
Earlier in the year the car was checked over. Fault codes hadn't been cleared for a while but the one unaccounted code suggested MAP sensor may be the issue.
To me, it seems too consistent to be a fuel issue or even spark plugs, leads playing up. Ignition off reset seems to point to electrical, and symptoms suggest the car is suddenly running lean or rich. I've read up on the other sensors but it doesn't sound like they would manifest in this way if misbehaving. The car lives inside and the atmosphere is pretty dry here in sunny Christchurch NZ. But local K series knowledge is a bit thin on the ground...
A few threads I've read are similar but not identical. Has anyone had this issue and confirmed the fix?
Got the fault codes read today...
Ambient air temperature sensor (not fitted on S1? Or is this intake air temp sensor?)
Throttle position sensor (already changed this with a spare, no effect)
Pressure sensor (MAP sensor?)
These codes were also read and cleared when I first had the problem. I would have expected O2 sensor may have shown too since I've had it disconnected but it wasn't there.
So where to from here? Would be great to get live data when fault is occurring but I don't have access to a portable diagnostic scanner for the duration I'd need it to try to get fault to recur.
Ambient air temperature sensor (not fitted on S1? Or is this intake air temp sensor?)
Throttle position sensor (already changed this with a spare, no effect)
Pressure sensor (MAP sensor?)
These codes were also read and cleared when I first had the problem. I would have expected O2 sensor may have shown too since I've had it disconnected but it wasn't there.
So where to from here? Would be great to get live data when fault is occurring but I don't have access to a portable diagnostic scanner for the duration I'd need it to try to get fault to recur.
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