P2187 and high LTFT - EGR Pipe Leak?

Technical Area Engine, Transmission, Exhaust etc
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  1. My model of MX-5 is: __ 2006 NC with NC2 engine
  2. I’m based near: Coventry
  3. I’m looking for technical help or recommendations on: P2187 Troubleshooting

Hi all, I had a dreaded CEL on the weekend, after reading and seeing it was P2187 “System Too Lean at Idle (Bank 1)” I started looking at fuel trims and O2 readings to figure out what’s wrong.

After some hunting I found that the cars stuck around 20% LTFT at idle, which drops to ~10% under load. Upstream O2 sensor readings are a bit odd, ranging from around 0.7-1.3V but mostly oscillating as expected. The car seems to run perfectly fine, except the occasional very small hunt for idle and it doesn’t smell rich as far as I can tell.

I’ve been spraying around the vacuum lines with some brake cleaner while hearing for an increase in idle (once engine is fully warm) and I’ve found a spot around the back which seems a likely culprit. When I directly spray the EGR Pipe nut, where it attaches to the EGR Valve, the engine virtually dies and then recovers. When I spray this area more generally the revs pick up slightly and then settle.

Would this suggest a leak in the EGR pipe is letting extra air into the intake? Before I go ahead and strip it down to replace I’m wondering if anyone else has had a similar experience or knows of other vacuum leak locations around this area. I can’t find any other leaks around the shutter valves, brake booster line, PCV lines, etc from the hunting I’ve done so far.

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My NC1 chucked this code a few yrs back, just after I filled the tank up.

I hunted and found no leaks.

Online search came up with possible loose filler cap , although the code for this is generally 440, 455 or 456.

I removed filler cap , cleaned seal , filler cap back on (minimum 5 clicks) and eml disappeared , never came back.

:thinking:

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This was my first move but no joy from the fuel cap or oil cap.

I got the engine bay torn down for access to the EGR pipe yesterday, low and behold the EGR pipe’s compression nut was only finger tight!

Waiting on a 22mm spanner to tighten it up properly and will add a drop of blue loctite for good measure, but will update if this solves the issue in the next few days.

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Big job , intake manifold off or did you gain access through windscreen scuttle?

If the manifolds off I’d chuck a new pcv valve on there whilst it’s in bits

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Thankfully I could gain just enough access with the scuttle and service panel off. I had placed an order for all the gaskets, PCV valve, etc to take the manifold off and refresh it while it’s all apart but I’ve been able to cancel that before shipping. She isn’t burning much/any oil so not too concerned on the PCV unless it’s apart anyway.

As long as the threads are in decent nick then it should be an easy fix, if the threads are F***ed then wish me luck :laughing:

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Fingers crossed bud :crossed_fingers:

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