Misfire/erratic idle on cold start

[Ep3-r]

My dc5 has a problem on cold start in that it sounds like it's misfiring for about 5 seconds with the revs bouncing from 500rpm upto 2000rpm and then it settles back to a normal idle. This problem only occurs after the car has been driven hard the day before, when it's not driven hard it idles fine from cold. This is the only time it misfires/sounds rough the rest of the time it is fine. Does anybody have any ideas? Thanks.

 

[JordanSuth]

I had the same issue although I didnt experience misfiring but more it kangaroo jump in lower revs. After a blast it would start to rev hunt on idle. Up and down from 500 to 2k. The problem was the ICAV. I replaced mine as they're so common for clogging up. You can remove it and clean it up. If you do make sure you remove the x2 five bit torx screws and lube the spinning shaft too or you'll still experience issues.

 

[Ep3-r]

Thanks for the reply Jordan, my iacv and throttle body have both been cleaned recently so I don't think that is the problem. When I drive the car hard using lots of vtec action it performs perfectly at the time, it's the following day from cold start when the problem occurs.

 

[JordanSuth]

That worked for me but if it hadn't I was going to have a look at my TPS sensor because they can throw up issues if they get faulty. Apart from that I am not sure but someone else on the forum might have had similar issues to you.

 

[Matt @ Torque GT]

Is your coolant level okay? IACV valves are notorious for being problematic where low coolant levels are involved. From there, try to get the live data checked on the TPS and MAP sensors.

If you need any parts, please just email hello@torque-gt.co.uk and I'll do what I can to source any parts you may need.

 

[Ep3-r]

Hi Matt, the coolant level is all good, can I check TPS and MAP with a multimeter? There is no EML light on either so no fault codes to check for. It's just strange that it only misfires on the next cold start after a spirited drive,the rest of the time it's perfect!

 

[Matt @ Torque GT]

Hi Matt, the coolant level is all good, can I check TPS and MAP with a multimeter? There is no EML light on either so no fault codes to check for. It's just strange that it only misfires on the next cold start after a spirited drive,the rest of the time it's perfect!

Sorry for the delayed reply - yes, you can generally check the MAP and TPS are changing their outputs with a multimeter. The TPS is quite a simple one, just measure the voltage with the ignition on as you cycle the pedal (0% to WOT) - should go from 0-5v (possibly 5v-0v) from memory, though I'm basing this on fault finding on my old MB6. The MAP is a little more difficult, you need to run the engine and check that the voltage changes with throttle input. Live data is the best way to confirm what percentages the ECU is seeing.