Warbling idle after repair...no codes?!

[ATCO99]

Basics: 1991 US Spec Elan M100, 49,750miles, +sport exhaust & generally in good condition ...apparently has after market ECU and new injectors but I cannot prove

Symptoms: On a recent 45 mile journey, engine intermittently lost power, rough running, coughing, gradually got more frequent and severe, with stalling when stopped and in neutral.
Action1: Replaced spark plugs and torqued to spec

Symptoms: Rough running & backfiring just 45 seconds after start...corrected to normal...then came back every couple minutes on local 4 mile drive, engine also lost power + stalled w/clutch in at stop signs
Action2: Replaced both coil packs, put original cables back on (new set were wrong lengths)

Symptoms: Warbling idle, struggling, spitting, tapping, sounds like tractor...car not driven, just engine starts
Action3: Performed paperclip test 1-2, 1-2, 1-2 .... 1-2, 1-2, 1-2 .... let it cycle 3x to be sure, same number sequence...no codes?

Hoping it is the plug wires (need a good source) unless someone out there suspects something else?

[Brit-Car-Nut]

Kingsborne Wires in San Marcos California
LOTUS ELAN SE M100 Series 1, 2 1991
800-643-0375

Their website doesn't show a price anymore but they are still in their catalog and they make them as ordered.

I believe you can order 7mm and 8mm versions as well as other assorted accessories

8mm wires don't fit in the "trees" that Lotus/Isuzu used.

Did you physically gap the new spark plugs?
(I am assuming you replaced the plugs with the correct STOCK specification: NGK BKR6E and set the gap to 0.8mm (0.031")

I would check the Cooling Temperature Sensor as it tells the Electronics what the engine needs.

See CTS Info

GM 8153263860 or GM 8250369790 or STANDARD MOTOR PRODUCTS TX3 Should be around $10.00 to $15.00 for a name brand. Rock Auto has the SMP version for $14.15

I am not aware of any "aftermarket" ECM for the M100 but there are a few companies providing different performance programs for the stock ECM.

Did you ever get a "check Engine Light"? If not, then there is no code set. If you did get a CEL, but then disconnected the battery, then the codes would have been erased.

Also, what history did you get with it when you bought it. How much have you driven it?

It would be nice to hear exactly what ECM you have. Also, were the coils "dry"? That is is there any chance the coolant tank has been leaking and getting the coil connections wet? The Ignition Control Module is also behind the coils, so if it got wet, it needs to be looked at and cleaned or replaced if it is corroded.

[wayne]

Hoping it is the plug wires (need a good source) unless someone out there suspects something else?

There's a set of Lotus OEM ones available here: https://www.ebay.co.uk/itm/Lotus-Elan-M ... SwRhVbhy6r

I ordered the Kingsbourne ones a few years ago and they have been great, cant fault them. (and probably a lot newer than the old Lotus set. (they have been sat on a shelf for a long time.

When my CTS failed, I did notice a lot of black smoke / soot from the exhaust.they may not all show the same symptoms.

[Giniw]

(Aren't the OEM red?)

[Brit-Car-Nut]

(Aren't the OEM red?)

Not on my car... Although it is 20 years old, it only has 20k miles and the wires are original.
They are black (but it is a US/FED car)

With mine being a NMY car, I ordered a set of BLUE wires from Kingsborne around 12 years ago and they are still sitting on the shelf.

[Giniw]

Mines were red (probably original but I can't be sure) and I have a new set (OEM — at least it's the right part number ^^') which is red.

https://paulmattysportscars.co.uk/lotus ... -last-one/ shows red HT leads too.

(OK, it's not that important thought )

And they were red on the press car too:
https://youtu.be/sJPZmnxasxc?t=95

[John_W]

(Aren't the OEM red?)

They were on mine.

[Brit-Car-Nut]

I guess UK / European owners get a better deal!

[Giniw]

[ATCO99]

Brit-Car-Nut
Thank you for the wisdom, I just ordered a set of 7mm red from Kingsborne, they were very helpful on the phone. I did not physically gap the spark plugs but they were 0.8mm and yes, NGK BKR6E, I just replaced them and torqued them to spec. No sign of water or coolant on the coils or the ICM but the ICM did have what looked like a piece of cellotape over the tiny dot in the center...I'll include a pic shortly as that looked odd to me. Throughout the 'rough running' sparking and backfiring the CEL was flashing on and off and I have not disconnected the battery. Not much history with the car I'm afraid and from Oct 2018 through Apr2019 it was in storage or repair shop so it maybe did 25miles, since I got her home I have put on maybe 150 miles but she always started up first time and vigorously until after the coil swap.

Wayne
No black smoke or soot from the exhaust but going to perform the CTS check this evening. I have taken a note of the OEM item on EBAY also, just in case

Giniw
My spark plug cables were red, thank you for the Paul Matty link

[John_W]

Oh goody. This sounds like an interesting one to solve!

Nil desperandum, we’ll get you going!

[Rambo]

OEM plug leads were in red. At least, otn his side of the Atlantic

From memory the OEM's were NipponDenso, as per the alternator

[Simon_P]

OEM plug leads were in red. At least, otn his side of the Atlantic

Yes red and individually numbered, they go black with age, if you can't read the writing they are just aged take a look at the ends and give them a scratch.

The replacement OEM leads are grey, and also have clear writing on them.

[ATCO99]

ICM.JPG

Photo of the ICM before I dusted/wiped clean. Is that piece of see through tape standard?

[Brit-Car-Nut]

Yes, it is normal.

Unfortunately, you haven't included the harness connectors which is what get corroded.

[ATCO99]

Brit-Car-Nut
Is this what you wanted to see? This is a different angle view of the ICM with the 2 new Coils clipped in, prior to refitting. The connectors that slide into these looked in pretty good condition, I don't remember corrosion or discoloration or moisture on them. Before I refitted them I sprayed fast drying contact cleaner on them and wiped a little vaseline in front of the concertina flanges just to make a water tight seal.

[Brit-Car-Nut]

I was actually wanting to look at the low voltage connections. They have a habit of getting corroded and not often noticed. Still hard to tell but after brightening the picture up, I don't see any obvious corrosion.

[ATCO99]

This is the old set of coils, they are in the same condition either side so showing 1 of each

[Brit-Car-Nut]

What I meant was the engine harness plugs: the 3 of them. I have seen several that have had the coolant tank or hoses leak and fill up the connections and once they are corroded, they can't be cleaned because the plating (cadmium?) on the pins goes away with the cleaning.

The coils and spark plug wire connections are rarely uncleanable.

[ATCO99]

I think I am with you now, in order to photograph those I will have to move the coolant header tank to one side or bleed it and remove it (it was one of the few parts I didn't document when I removed everything). From memory, the insides did not look corroded which may have been why I didn't photograph them but worth a check

While I am here, can i confirm which is the CTS from the diagram you linked earlier...in my photo I think it is (#1) but (#2) also has 2 wires although it is perpendicular to the Rad Fan thermal switch (#3) rather than beside