MX5 starting problem

[Joeigglypuff]

Have tried posting this in the MX5 forum but not had much luck. Hoping someone here can help.

I have a problem starting my MX5 mk2 (1999) when hot. It's also got a idle that dips but I've read that will be sorted out by itself as the ECU learns.

The starting problem is quite troubling though. Every semi-long journey (say, more than 30 mins) it won't start if left for 10 mins or so. But then it will start after 20-30 mins. It's definitely to do with heat as if it's left with bonnet up to cool down it works fine. It also sometimes, when at the edge of cooling enough to start, almost catches when turning over and a foot on the accelerator allows it to spurt in to life. Other times it'll just keep turning over with no sign of starting.

I've already changed the coil pack and HT leads so it's definitely not that, and I also (on a PH-ers suggestion) changed the MAF sensor but nothing has worked so far. It runs fine when on so it's still use-able but not nice knowing it might not start every time i get in it.

Any suggestions?

[JC2012]

Get it scanned on a fault scanner.

It could be a Crank Sensor playing up?

[feef]

Crank OR cam sensor, no real way of knowing which one, so flip a coin and hope you pick the right one (although if one is going, it's probably not a bad idea to replace them both: similar sensors, similar age)

[Joeigglypuff]

Thanks for the advice guys, I have ordered new sensors (cam and crank).

Hoping one of those fixes it as it's costing a fair amount to keep ordering new parts whilst attempting to fix this. Still cheaper than going to a garage though, and it only means these things won't fail in the near future so not too bothered!

Please let me know if anyone else has other suggestions.

[SebringMan]

Be careful of buying new parts, it can be a terrible trap to get caught up in. It could even be the fuel pump etc.

Is this car an OBD type or does it require the old LED trick in the diagnostic port?

[Joeigglypuff]

SebringMan said:

Be careful of buying new parts, it can be a terrible trap to get caught up in. It could even be the fuel pump etc.

Is this car an OBD type or does it require the old LED trick in the diagnostic port?

I know but so far these are quite cheap so not too worried. The diagnostic port is one of the old ones with the LED trick, engine returns no fault codes but I can't really say I know if I'm running the right test.

[feef]

cam/crank sensor issues are a common cause of hot start issues on the MX5, and it tends not to show up on the diagnostics either

[Joeigglypuff]

Thanks for you help all. I fitted a new cam and crank sensor and all seems well again so far - idle droop still exists but isn't as heavy and is infrequent, but have tried starting it after a long journey a couple of times now and it seems to be all OK. If anyone else has this problem I would say try those first - cheap fix if you can find the sensors on eBay!