misfires and rough idle - LotusTalk - The Lotus Cars Community
 
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post #1 of 6 (permalink) Old 07-23-2017, 04:41 PM Thread Starter
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misfires and rough idle

2008 Lotus Elise SC, 18000 miles. Suddenly started misfiring, idling up and down. I pulled the plugs and coilpacks and found three to be seriously rusty. I replaced them with new plugs and coil packs with dielectric grease all over outside of the coils, inside the plug boots trying to avoid the electrode, and on the plug porcelain. Antiseize on the plug threads. No change in misfiring/rough idle.

No check engine light. Misfiring/rough idle doesn't start until after a minute of running. Before this it starts right up and idles smooth.

I plan to change air filter/clean the MAF and throttle body.

If this doesn't work what is next step?
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post #2 of 6 (permalink) Old 07-24-2017, 01:38 PM
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Swap ECU with one that you know works if you can find one to borrow locally. If that solves it then there ya go...

Sent from my SM-G955U using Tapatalk
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post #3 of 6 (permalink) Old 07-24-2017, 05:14 PM
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If cleaning the MAF doesn't help, I suggest you also try cleaning the throttle body electrical connectors, since the DBW throttle controller also controls idle air (there's no separate idle air controller like there is on older cable-style throttle bodies). That fixed an idle problem on my '08 when it was still relatively new, the dealer cleaned the electrical connections with "Stabilant 22".

If that doesn't help, I suggest you hook-up an OBD-II scanner, start the engine, and check the coolant temperature, intake air temperature, and front ("bank 1 sensor 1") O2 sensor readings, bad data from any of these can screw-up idle. For coolant and air temps, just check to make sure the temperatures make sense (should be around ambient at cold start). For the O2 sensor, it should start out reading rich (above 0.5v, likely 0.8-0.95v), but then after a minute or two it should oscillate up and down across stoich (=~0.5v). Since it initially idles OK, it may be that the idle goes bad when it switches from open loop to closed loop, and the O2 sensor may be the problem. Could also be fuel related, on cold start there's an initial period of fuel enrichment that might mask a low fuel pressure problem, but I think that's less likely.

HTH, -Ed

-Ed
'08 Arctic Silver Exige S240
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post #4 of 6 (permalink) Old 07-24-2017, 05:20 PM
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I recently had a very similar problem, check the little black ground wire on the left side of the engine. Mine was marginally lose and i spent two weeks and tons of replacement parts trying to fix it. I think i have a picture of it in one of my other posts, but I'm on my phone now. Good luck .
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post #5 of 6 (permalink) Old 10-18-2017, 10:04 AM Thread Starter
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Followup: After about six weeks of diagnostic effort by by my local indie to no avail, I took it down to Waldir at Intermeccanica (Mamaroneck NY) and he found the ECU was shorted out by water. Nice call DeafPaul! How common is this? I'm never gonna wash it again...
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post #6 of 6 (permalink) Old 10-18-2017, 01:49 PM
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Quote:
Originally Posted by vg569 View Post
Followup: After about six weeks of diagnostic effort by by my local indie to no avail, I took it down to Waldir at Intermeccanica (Mamaroneck NY) and he found the ECU was shorted out by water. Nice call DeafPaul! How common is this? I'm never gonna wash it again...
Just curious... how long has your car been at intermecanica?
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