Fast idle, poor starting and crackling sound on acceleration
Discussion
Hi guys,
Over the last couple of weeks I've noticed my '96 Mk1 1.8 would sometimes stick idling at about 1500 rpm rather than dropping to 750-1000 when coming to rest in traffic. This would happen from cold or warm. It would normally then drop to back to under 1000 after resting at 1500 for a few seconds.
This morning I noticed this again but perhaps slightly more pronounced and on my way back from the shops the car really struggled to start. It hasn't done this before but would fire up and then seem to be misfiring and would die immediately, only running once I'd given it a rev for 30 seconds or so. On the couple of miles back home after it seemed absolutely fine until towards the end of the journey I noticed what sounded like an electrical/crackling noise under the bonnet whenever I touched the accelerator.
I'm going to look to change the plugs as I have a spare set lying around. I last replaced the HT leads about 4 years ago due to a misfire at 3000rpm and have read about idle problems with a green temp sensor but was wondering if you guys had any other suggestions.
Many thanks!
Over the last couple of weeks I've noticed my '96 Mk1 1.8 would sometimes stick idling at about 1500 rpm rather than dropping to 750-1000 when coming to rest in traffic. This would happen from cold or warm. It would normally then drop to back to under 1000 after resting at 1500 for a few seconds.
This morning I noticed this again but perhaps slightly more pronounced and on my way back from the shops the car really struggled to start. It hasn't done this before but would fire up and then seem to be misfiring and would die immediately, only running once I'd given it a rev for 30 seconds or so. On the couple of miles back home after it seemed absolutely fine until towards the end of the journey I noticed what sounded like an electrical/crackling noise under the bonnet whenever I touched the accelerator.
I'm going to look to change the plugs as I have a spare set lying around. I last replaced the HT leads about 4 years ago due to a misfire at 3000rpm and have read about idle problems with a green temp sensor but was wondering if you guys had any other suggestions.
Many thanks!
Update:
Well I changed the spark plugs, started up perfectly and I went for a drive. Everything seemed fine except it was still idling fast. Stopped a coupla times to see if it was starting ok when warm but seemed a bit hesitant the 2nd time. I foolishly left the lights on the other week so had almost killed the battery so thought perhaps it had hesitated because I'd stopped a couple of times without letting it re-charge. Anyway, I went for a longer drive along the dual carriageway when again it started to make an electrical/crackling noise from what sounded like the front left of the car. This grew worse so I pulled over at which point the car refused to start at all, it seemed completely dead, not even turning over. There was also a little smoke coming from somewhere around the exhaust manifold heat shield.
Called the AA out and by the time they came it started perfectly again and they followed me home without issue except for the crackling sound on acceleration starting just before home and the car not idling below 2000 rpm.
Any guidance as to what might be up would be great.
Well I changed the spark plugs, started up perfectly and I went for a drive. Everything seemed fine except it was still idling fast. Stopped a coupla times to see if it was starting ok when warm but seemed a bit hesitant the 2nd time. I foolishly left the lights on the other week so had almost killed the battery so thought perhaps it had hesitated because I'd stopped a couple of times without letting it re-charge. Anyway, I went for a longer drive along the dual carriageway when again it started to make an electrical/crackling noise from what sounded like the front left of the car. This grew worse so I pulled over at which point the car refused to start at all, it seemed completely dead, not even turning over. There was also a little smoke coming from somewhere around the exhaust manifold heat shield.
Called the AA out and by the time they came it started perfectly again and they followed me home without issue except for the crackling sound on acceleration starting just before home and the car not idling below 2000 rpm.
Any guidance as to what might be up would be great.
Edited by MG-FIDO on Thursday 29th May 12:55
Well, I went and had another peak at the car as the chap in the garage up the road kindly fitted me in to take a look. The coolant overflow tank was empty and I couldn't see anything in the radiator either. In the end it took about 4 litres to fill it up. So, the crackling sound does seem to have been it over heating and the smoke was oil burning due to the heat.
We couldn't see any fluid leaking but I had only checked the levels about 2 weeks back. Afterwards I went for another drive without issue, but did notice a bubbling sound which was coming from the water in the overflow tank boiling once I'd stopped which was disconcerting. I put a bit more water in, I think I need to add some coolant and keep my eyes peeled for leaks. Didn't seem to be idling fast either.
I'm a bit confused as to whether all this was due to it overheating and how this happened having only checked in the last couple of weeks unless it was still warm when I last checked and I wasn't getting a true reading.
We couldn't see any fluid leaking but I had only checked the levels about 2 weeks back. Afterwards I went for another drive without issue, but did notice a bubbling sound which was coming from the water in the overflow tank boiling once I'd stopped which was disconcerting. I put a bit more water in, I think I need to add some coolant and keep my eyes peeled for leaks. Didn't seem to be idling fast either.
I'm a bit confused as to whether all this was due to it overheating and how this happened having only checked in the last couple of weeks unless it was still warm when I last checked and I wasn't getting a true reading.
Thanks again Vlad, checked this morning when cold and the overflow was empty and couldn't see any fluid in the radiator. Topping both up took a good litre or more, the garage up the road have also suggested the thermostat so I've left it with them to take a look. I'll let you know what they think.
Hmm. Bubbling in the header tank does not sound great. Many things it could be from thermostat as suggested, airlock, water pump to head gasket or cracks in head / block.
If you imagine that the water pump is not circulating the water around the engine because of an airlock or pump failure, then it will get hot in the block as combustion takes place alongside the stationary water, boil and the steam will look for the easiest escape - which is the header tank. Similarly, if you have a head gasket problem between a cylinder and a water gallery, then the compression will escape into the coolant, and take the easiest escape again - the header tank, and bubbles. In both cases, there will be heat too. Same with cracks, also seen it on lifted wet liners (not sure if the 5 is wet lined).
If it is this type of problem, you may not find any leaks. It may be escaping via the overflow as heat and the pressure increases. I would get it looked at ASAP and really keep an eye on the temperature when driving. I am not sure how hardy the mx5 lump is, but overheating can warp cylinder heads on cars and do a lot more serious damage as the oil loses viscosity with heat. It sounds like you have had a pretty hard brew already if you could hear it inside the car when driving.
Seriously, get it to someone that knows what they are doing. Losing that amount of water without obvious signs of leakage is not a good thing.
If you imagine that the water pump is not circulating the water around the engine because of an airlock or pump failure, then it will get hot in the block as combustion takes place alongside the stationary water, boil and the steam will look for the easiest escape - which is the header tank. Similarly, if you have a head gasket problem between a cylinder and a water gallery, then the compression will escape into the coolant, and take the easiest escape again - the header tank, and bubbles. In both cases, there will be heat too. Same with cracks, also seen it on lifted wet liners (not sure if the 5 is wet lined).
If it is this type of problem, you may not find any leaks. It may be escaping via the overflow as heat and the pressure increases. I would get it looked at ASAP and really keep an eye on the temperature when driving. I am not sure how hardy the mx5 lump is, but overheating can warp cylinder heads on cars and do a lot more serious damage as the oil loses viscosity with heat. It sounds like you have had a pretty hard brew already if you could hear it inside the car when driving.
Seriously, get it to someone that knows what they are doing. Losing that amount of water without obvious signs of leakage is not a good thing.
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